In our 2006 annual Kitchens & Baths issue (Fine Homebuilding #183) you’ll find a primer on the concept of hot water recirculation, a plumbing strategy designed to provide homeowners with instant hot water at the tap, ultimately saving their time, water, and money. No doubt about it, recirculation is a step in the right direction. The best way to set up a system however, is a bit more contentious. To continue the discussion and to help answer your questions about hot water delivery, we’ve invited two industry experts (see bios below) to moderate a thread on “Breaktime.†They’ll be checking in daily. Let the discussion begin…<!—-> <!—-><!—->
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Meet the experts:
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Gary Klein<!—-> <!—->
<!—-> <!—-><!—->Gary<!—-> <!—-> has been intimately involved in energy efficiency and renewable energy since 1973. In 1975 he earned a BA in Technology and Society with concentrations towards energy conservation, efficiency, and environmentally appropriate technologies. One fourth of his career was spent in <!—->Lesotho<!—->, the rest in the <!—-><!—->USA <!—-><!—->. <!—-> <!—->Gary<!—-><!—-> has a passion for hot water: getting into it, getting out of it, and efficiently delivering it to meet customer’s needs. He currently works in the Demand Analysis Office of the California Energy Commission and chairs the recently formed Task Force on Residential Hot Water Distribution Systems. <!—-> <!—->Gary<!—-><!—-> has published over 25 articles on topics including energy efficiency, renewable energy, and hot water delivery.
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Dave Yates<!—-> <!—->
Born and raised in <!—-> <!—->York<!—->, <!—->Pa. <!—-><!—->, Dave began his career in the PHVAC trades in 1971. After serving his apprenticeship and working his way to Master Plumber status, Dave struck out on his own in September of 1979. In 1985, Dave returned to the company where he had served his apprentice years and purchased F. W. Behler, Inc., a third generation PHVAC firm which is celebrating 106 years of service this year. Dave’s company has won numerous awards for their work and he is the recent recipient of the Carlson-Holohan Industry Award of Excellence. A published author in numerous trade publications in the <!—-><!—->USA <!—-><!—-> and overseas, Dave has also written articles for The World Book Encyclopedia. In addition to teaching and lecturing throughout the <!—-><!—->USA<!—-> <!—->, Dave was recently hired as an Adjunct Professor at the Thaddeus Stevens College of Technology. Over the course of his career Dave has designed and installed just about every type of hot water recirculation system
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I'll bite.
Is there hard evidence that recirculating DHW saves money? How much per year for the typical family of 4? What is the simple payback in years on the incremental cost of the system? What is the incremental cost in dollars for a typical new 2500 SF house with 3 bedrooms?
Depending upon use patterns, recirculating hot water could easily incur larger water heating energy costs due to standby losses in the loop. How much larger in dollars per year? I really don't know, so am welcoming input from those who do.
This could be a very interesting thread. Expert moderators is a new move for Breaktime, and that will also be interesting.
Bill
Hi Bill,<!----><!----><!---->
Excellent question and one I get often from folks interested in rcirc systems. At first glance it looks like it should cost more, not less, to circulate heated water out to some remote point and back to its heat source. If the distribution lines remain uninsulated, that can become a reality. A well-insulated circuit, on the other hand, does an excellent job of conserving and containing potentially lost energy.<!----><!---->
The most frequent complaint that brings us into the picture is the long wait for hot water. It’s not uncommon for that wait to last for one to two minutes until the bather is comfortable with the adjusted delivery temperature. Toss in a family with several bathrooms and the potential exists for large volumes to be wasted. Taco indicates 14,000 gallons for a family of four (Taco-HVAC.com); Laing (lainginc.com) indicates 8,000 to 20,000 gallons; and Grundfos (Grundfos.com) includes a chart based upon pipe size, length of run and daily usage that shows 9,855 to 55,115 gallons of wasted water per year. <!----><!---->
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Let’s assume an average of 12,000 gallons wasted per year in my own home (which is not the case because we have a recirculation system). My water bill at home lists an average charge of .007 per gallon. That comes to $84.00 down the drain – literally. If I utilize an 82% efficient means of heating that wasted water from an average temperature of 55F (degrees Fahrenheit) to 140F, that will cost me $138.33 if one cubic foot of natural gas costs .01335 (my average cost for natural gas this year). Toss in 18% (wasted water portion of annual use) of our yearly sewage treatment bill for an additional $52.79. My total would come to $275.12. <!----><!---->
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A 33-watt pump utilized two hours each day will cost $2.22 per year at my current rate of .092 cents per kWh. Couple that with energy lost via well-insulated piping heat emissions of $14.62 annually and you’ll see a net savings of $258.28 for this application in my home.
My master bath bathing module is the farthest point from my indirect water heater (a well-insulated SS tank that only looses 1/2 of 1 degree per hour) that's driven by a high-efficiency modulating/condensing boiler, yet the hot water is there before anyone can step in. It only travels four feet from the recirculated line until exiting the shower head. Virtually instant hot water.
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Thanks,<!----><!---->
Dave Yates <!----><!---->
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Thanks, Dave.Now I know that a properly designed system saves money on both water and energy. The gallons/year figures got my attention. For me the water waste is a more compelling reason to do the system than either the energy or the money wasted.Although you did not address that aspect of my initial question, I can guess that the incremental system costs in a new house would have a simple payback of under a decade.What are the prospects for retrofitted systems in existing homes? A client of mine has a system that was retrofitted without any new piping in their walls, and they are happy with it. I don't know how it works. How do systems like that work, and do they also save net money, even if not saving any energy?Bill
Bill,<!----><!----><!---->
I feel the same way about wasting water. Tell you the truth, that was not why we have been installing hot water recirc systems since the advent of water heating and folks hating to wait. It's always been a convenience want-to-have instead of a need-to-have. Conserving resources is the icing on the convenience cake! If you look at the ROI (return on investment – the term “payback” has proven to be a sales killer for me) vs. the installed cost, it might look like this: cost of installation - $550.00; annual savings - $210.00; ROI = 38% (divide the savings by the installation cost). That’s a tax free ROI too. <!----><!---->
Actual cost savings vary considerably and are largely dependent on the owners and family, if any, and their personal habits. If teenagers live there, hot water use can be very high as they tend to stay in the shower until they're no longer teenagers!<!----><!---->
There are a wide variety of recirculation methods/systems and, they too, have varying cost levels depending on sophistication. New construction is the easiest installation and least expensive with costs ranging from a few hundred to almost a thousand if it's a more complex multi-zoned recirc system. Smaller homes are naturally less than a McMansion. Copper has been priced like a precious metal here of late and PEX has largely taken over (in my area). If expansion is an issue, PAP (PEX-Al-PEX) tubing can be utilized. PAP has an aluminum layer sandwiched between an inner and outer layer of PEX and has just about the same coefficient of expansion as does copper.<!----><!---->
Retrofitting into an existing home is relatively easy with the kits available from multiple manufacturers. Either a dedicated return line must be installed or a cross-over “bridge” must be created to allow the cold water line to act as a temporary return to the heat source. In those applications, a temperature sensor monitors the cold water line and shuts off the recirc pump at 90 to 100F. If the owners don’t mind a temporary bit of warm water delivery from the cold tap, that can work quite well.<!----><!---->
Yes, they too will save money. How much depends on actual run times and the installer’s attention to details like insulating the piping. <!----><!---->
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Edited 10/17/2006 5:37 pm ET by PAH
Thanks. My clients have a system where the cold is the loop return. The warm water at the cold spigots is odd, but not a real problem. I'm sure none of the in-wall lines are insulated, so they are using radiant wall heat in their home (but not very much of it).The 38% ROI sounds like a slam-dunk for new homes. If I ever build another new home I'll look into it. My work is all remodel work.Obviously, a smaller home with a compact mechanical core doesn't benefit much from recirculating hot water. Sadly, this sort of design is very rare in our bigger-is-better culture.Bill
The ROI for retro-fits can be just as good! Most folks today have IRA's or some other form of investment and understand their investments yield far less than the ROI I can show them for any number of energy conservation measures - including recirc systems. Sales 101 stuff learned in the school of hard knocks. Sell myself first, present the choices with ROI's and let the customer decide. More often than not, they'll chose the more expensive up-front investment that grants the larger ROI.
Dave,
I've seen hot water recirculation systems designed and installed in different configurations. Some use a bypass at a distant fixture. Some use a tee in the tank drain. Some feed the recirculated HW into the cold water supply line to the water heater. These are the most prevalent that I have seen, I'm sure there's more.
Based on your experience, is one prefereable to others? Why?
My first preference is gravity, but that isn't always possible. When the need arrises to utilize mechanical power for the work, the job site conditions will dictate which method we ultimately choose. While at ISH-NA in Chicago recently, Wilo (pronounced Vilo) revealed they're going to be introducing a 1-watt/1-GPM pump later this year to the US market and that they'll have a version for domestic recirculation. It has a 14-volt DC motor and the speed/flow can be modulated. When installing any recirc system, we prefer a dedicated return line so that we're not warming the customers' cold water line. If we can't find a way to install a dedicated return, the cross-over bridge is used - either under a vanity or back at the water heater. If just one branch is to be treated and the vanity location doesn't lend itself for easy use (electricity & wiring can be difficult), we have installed the cross-over between hot & cold in the branch lines shortly after they've left the mains or just prior to their disappearing up through the wall. Edited 10/17/2006 5:40 pm ET by PAH
Edited 10/17/2006 6:39 pm ET by PAH
I like the idea because it simply allows the end user instant hot water, but more clients are insisting on greener technologies, not only those that work better.
What are some ballpark numbers for upfront additional costs of the "well insulated" circ system, as well as long-term cost of the pump (replacement)?
We've gone with on-demand hot water heaters located closer to where they are actually used with great results. That combined with 1/2" pex home runs from each point of use to one of the hot water heater locations makes more sense on the surface to us, but perhaps we're not seeing something.
Beer was created so carpenters wouldn't rule the world.
Mornin Don,
Last week I visited a job site and discovered a recirc system that was installed in 1948. Still chugging along with a B&G series 100 bronze circ running 24/7! Today's circulators for potable water circulation are typically (in residential apps) a wet rotor (meaning there's no oiling or maintenance to perform) pump and the wattages continue to get smaller - as low as 25-watts. The cost continues to drop for these circs as they get smaller and they're consuming less power to perform the same task.
The costs can't be pinned down without knowing what will be involved for materials and labor, but we see an average of $500.00 to $1,000.00 for installed systems. If we were working on a new housing project where a builder was utilizing a series of designs, we would develop a set price based upon those factors so that the builder could add that to their package. Typically, they will add a percentage or flat fee to our price of 15% to 30%. To a consumer, that might seem unreasonable, but it's well earned as the builder must spend time with the client and time with us coordinating the installation and ensuring its installed to specifications. Just as we do, the builder warrants the work to be free of defects and if the mechanical sub walks away from a problem, the builder gets stung for the repairs.
On-demand, or tankless, water heaters can be a great thing - if they're installed correctly. As you pointed out, they're designed for more of a point-of-use application than a whole-house solution. That said, there are models available that incorporate a small electric heating element so that recirculation and "instant" hot water can be available at remote locations. The issues surrounding the use of on-demand water heaters are numerous - so numerous, I've developed a 90-minute presentation for mechanical contractors and will be taking that "on the road" next year.
We've done recirc with home-run PEX systems. The bathing module is typically the fixture targeted. Or, if the manifold is remotely mounted (close to the bathroom group - in an addition for instance), we've also added recirc to treat the manifold so that all fixtures attached utilizing hot water get rapid results.
Thanks for the info. It makes sense that a small recirc pump isn't the same beast as would be found in a radiant heat system, so reliability is higher and replacements further between.
What kind of insulation is required? We currently insulate all interior walls and floors with unfaced fiberglass bats, so if the fiberglass would be sufficient for heat retension it cuts down on our costs. My guess is the fiberglass allows too much air movement within the walls for the large temp differential so we'd have to use a foam wrap anyway. (?)
Beer was created so carpenters wouldn't rule the world.
Sorry for the late arrival to this group. I have been travelling and Internet access was not working. My apologies.
Several comments.
1. The cost of operating a recirculation loop is mostly in the heat loss of the loop, not in running the pump. This is particularly true for the relatively small systems installed in most single family residential applications. A simple rule of thumb is 90 percent goes to the heat loss in the loop and 10 percent to the pump. If you pick the wrong type, you can easily double the cost of water heating.
2. It turns out that there are six types of recirculation systems. These are:
Thermosyphon
Continuous recirc
Timer controlled recirc
Temperature controlled recirc
Time and temperature controlled recirc
Demand Controlled Recirc
The most expensive to operate is the continuous recirc, followed by the thermosypon. Essentially the only difference is the extra cost of operating the pump. The operating costs of the next three systems depend on the hours of operation. The only type that uses less energy than is associated with running water down the drain while waiting for hot water to arrive is Demand controlled recirc. It can be installed in new construction and in retrofit.
I would like to refer all participants to a series of articles that have appeared in IAPMO's Official magazine that go into this issue in some depth. I will have a location to read these articles in a day or so.
3. Research done by the California Energy Commission has found that low flow rates in pipes, say 1 gpm or less result in relatively large temperature drops. In fact, at some combination of low flow rate, relatively long distance and adverse environmental conditions, hot water will never get to the fixture.
What is interesting for this discussion is that low flow rate recirculation pumps will also result in relatively large temperature drops between the time the water leaves the water heater and when it returns. If the flow rate is 1 gpm and the temperature drop is 5F, then it takes roughly 300 therms to keep a recirculation loop warm if it runs 24/7. It doesn't matter if the loop is insulated or how long it is, what the water heater sees is the flow rate and the temperature drop.
The research showed that halving the flow rate roughly doubles the temperature drop and doubling the flow rate, halves the temperature drop. Of course, insulation reduces the temperature drop compared to uninsulated pipes in air, roughly in half for a given flow rate.
4. I wonder if any of the readers could measure the temperature drop of one of their recirculation systems and estimate the volume of the loop and the flow rate.
5. Here are three questions to noodle on:
How many hours a day do you actually use hot water?
When do we actually want to operate a recirculation loop?
How would you deliver hot water to every fixture in a house using no more energy than is currently associated with running water down the drain and wasting no more than 1 cup while waiting for the hot water to arrive?
Looking forward to continuing the discussion. Gary
Gary, any idea of what the limiting factors are for preventing erosion of copper recirc lines using pumps?
Deburr all cut ends.
Size pump & lines not to exceed 5 fps--- feet per second.When asked why is there four engines on a 747------ "cause we couldn't fit six" a Boeing engineer
Gary, if you don't mind, I'd like to take a stab at this one.
Rich, from my experienced with recirc line failures, I've come to a few conclusions relating to the limiting factors you speak of.
In no particular order (the sign of a cluttered mind) here's my list.
Limiting excess velocity by sizing the return loop no less then 3/4".
Using L rather then M copper won't limit erosion, but it will make it that much harder for erosion to cause a pipe failure.
Reaming the ends of all copper tube before fitting is a must.
Keeping temp in the recirc line below 140ºF (as explained to my by Jim Weflen of the Copper Development Assoc.). Temperatures above 140º cause chemical reactions that enhance erosion corrosion by facilitaing the sluffing off of the mineral covering on the inside walls of the tube and fittings.
Use water soluable flux. Flux residue is death to copper.
Limit changes of direct, which are a major cause of turbulance, in your return line where ever possible and use 45º elbows and/or long sweep 90º elbows when changes of direction are unavoidable.
Avoid excess water pressure. The higher the pressure the greater the velosity.
When sizing your pump, the lowerest head that will achieve recirculation is best. Higher head, more velocity, and more cost to run.
Timers and aquastats are also a good idea. They save money, as described above, and by limiting the contact time of pipes and running water, they extend the life of the system. That's all that I can think of.
Scott Denny
I think the biggest problem may be related to pressure.
Heating systems have all of these problems, but most run 15 - 20 psi.
Don't forget oxygen?
I don't know if anyone is reading this thread still, but here is what I did for a recirc system:
I had a recirculation pump with a dedicated return line and a timer for several years but it bugged me because most of the time the pump was running it was not needed *and* a lot of the times I wanted hot water, the pump was not running. I just finished installing a unique "on-demand" control that turns on the pump when I turn on the hot water anywhere in the house.
A diagram of the setup is at: http://i480.photobucket.com/albums/rr167/PRYGAARD/RecirculationControl.png
<!---->1) On the cold water IN on the Hot Water tank, I put a flow switch that turns on when it detects flow. (Note: This can *not* be anywhere in the circulation loop)
<!----> <!---->2) The flow switch turns on a Delay-Off timer that turns on the pump immediately, but does not turn it off for 80 seconds after the switch is turned off.
<!----> <!---->Now, when I turn on the hot water, the pump comes on and I get hot water fairly quickly. The neat thing is this: I can turn the hot water on for a second and then turn it back off...but the pump keeps going for up to 80 Seconds. I then just wait for a little bit and when I turn the Hot water back on...it is hot and ready to use. However… 80 seconds after I quit using the hot water, the pump turns off till the next time there is demand.
Parts I used:
Flow Switch: I used a Gems 26615 because I got it cheap on ebay. (http://www.gemssensors.com/ApplicationSearchResults.asp?nQuestionID=36 ) Others are available, but be sure to get one that has a fairly low trip point on the flow. (.75 – 1 GPM)
Delay off Timer: I used an MX046 timer kit.(http://www.bakatronics.com/shop/item.aspx?itemid=466) I had to build it into a case, but it seems to be working well. There are other delay-off timers and relays out there but this seems to be the cheapest option. (Yes… I am all about keeping the cost of my projects down)
Note: The delay off timer is not needed if you are willing to give up the trick of turning the hot water on for a second and then waiting for a bit.
Edited 12/21/2008 1:49 pm ET by prygaard
Edited 12/21/2008 1:52 pm ET by prygaard
Edited 12/27/2008 10:31 pm ET by prygaard
I am renovating an old house and took up the issue of having to wait for hot water with my plumber. As a result I am considering installing an on-demand/tankless type of heating system using natural gas. I have a kitchen and washer/dryer at one end of the house and bathrooms at the other, so I figured on installing two of these units. Any thoughts on this system compared to recirc (apart from the fact that my up-front cost is rather high)?
I'm curious if any of you turn off you recirculating loops during the summer. The hot water loops in our house are gravity operated. (no pump) They have a shutoff valve where the line returns to the water heater. When the AC is running I think it's foolish to have hot water circulating around under the floor. So when the AC goes on the loop goes off. Just curious if anyone else does this...
Expert: Someone that takes a subject you understand and makes it sound confusing.
We don't turn them off. The goal is quick hot water at the faucet--convenience, not saving water or energy. That it should save water and energy is a good thing, too, but the goal is convenience, so it runs all the time. Lines are insulated, so limited effect on summer slab. The only thing I'd have done different is insulate the cold water lines, too. Never entered my lil' brain.
Mine runs 24/7
60' of it is 1/2" & 10' of it is 3/8"---- had to snake it some finished walls to get it to my remote fixture.When asked why is there four engines on a 747------ "cause we couldn't fit six" a Boeing engineer
My problem is a little different.
I am involved as a House Committee chair for a residence of about 18 years old. When new, the domestic hot water was only passable. Now, it's severely deficient.
It has a furnace fired hot water system for radiant heating as well as a 70 gal (US) holding tank. The residents complain about lack of hot water all the time. The mechanical room is at the west side of the house and the bathrooms are all over the second floor. The house is about 6500 sq. ft.
Our HVAC guy is coming in on Tuesday to remove the tank & clean it out, as a first step.
I can ask him about a recirculating system but I can't open walls. What's the best way to get these folks enough bathing water?Quality repairs for your home.
AaronR ConstructionVancouver, Canada
There's probably 75 feet of copper between the hot water tank and my master bath, which is on the north side of the house (did I mention I'm in Michigan?). I investigated the 'on demand' system highlighted in issue #192 (Metlund), and it sounds great to me. What I don't like is the button or motion sensor needed to activate the system. It seems more appropriate to just use a flow switch upstream on the hot water line. Is there something wrong with this? Any additional check valves that would need to be used if I utilized the cold water as the return? (placing the 'bridge' just before the first fixture on that line)Thanks in advance for your time
I'm interested in what you say about recirc in home-run systems. I wanted to do this in a new house (also using a Rinnai tankless) and was told by my plumber it couldn't be done. How would you set this up?
Thanks
recirc,
Related to Rerun? (Just kidding!)
Rinnai no doubt wants to avoid all of the bad things that can happen when attempts are made to incorporate a tankless unit in the recirc loop. For starters, their min input is 15K Btu's & 100' of 1/2" PEX only holds about 1-gallon of water. At 70F rise and assuming you could hit the min flow rate to trigger the burner of .5-GPM and keep the burner firing at its lowest rate, you'd only get a 2-minute run-time. And, that'd be the first cold-cycle-only as subsequent cycles would see a much higher return temp. Following that cold-start, the remaining cycles would be 20-seconds (or less) of burner run time for a 10-degree-F delta-T aquastat setting (burner on at 110F - off at 120F).
There are several methods that can be used to get "hot water - now":
* Recirc utilizing a small electric tank-style water heater with it's supply loop connected after the tankless and its return side as close as possible to the target fixture's hot line. Timed, sensor or constant circ can be used. BTW, Wilo is about to introduce a 1-watt, 1-GPM recirc pump that will be ideal for most recirc systems. In a home-run system, you'd connect the supply just past the manifold to the target fixture's hot line. Insulating the entire re-circ loop will help reduce parasitic energy losses.
* An in-line tank-style electric water heater can be located as close as possible to the target fixture with its "cold" inlet seeing the hot water delivered from the tankless. You'd need to calculate the volume of the initial cold-water slug to determine how much of a temperature drop might occur & if that will be noticed.
* Install the tankless in close proximity to the target fixture. If other bathroom groups require "hot water - now" as well, multiple tankless water heaters can be installed. We're seeing more & more installations where two, or more, tankless units are being installed.
XXX: Not recomended: install a recirc pump with sufficient power to overcome the high-head loss through the tankless to trip the burner's trigger. Often voids the tankless warranty & will run it to an early grave by short-cycling the control and burner components. Also generates higher electric bills.
Thanks. I think we will be doing a modified manifold system--two or three zones each with a return into a main return just before the pump that pulls the water through the system. Does that make sense. I will try to find out more about the Wilo pump. If I have to make a decision before their new pump comes out are there pumps you prefer? We will have 250-300 feet in the loops. The house is two story--two baths up and two baths down. Total of 4,000 sq. ft.
* Recirc utilizing a small electric tank-style water heater with it's supply loop connected after the tankless and its return side as close as possible to the target fixture's hot line. Timed, sensor or constant circ can be used. BTW, Wilo is about to introduce a 1-watt, 1-GPM recirc pump that will be ideal for most recirc systems. In a home-run system, you'd connect the supply just past the manifold to the target fixture's hot line. Insulating the entire re-circ loop will help reduce parasitic energy losses.
In a large house, with many possible users, a typical 6 gallon elec wh, w/3/4" inlet and outlet, is fine when only one fixture is demanding hot water, but could be a source of flow restriction when many fixtures are in use.* An in-line tank-style electric water heater can be located as close as possible to the target fixture with its "cold" inlet seeing the hot water delivered from the tankless. You'd need to calculate the volume of the initial cold-water slug to determine how much of a temperature drop might occur & if that will be noticed.
I've never met a homeowner who only had one target fixture.* Install the tankless in close proximity to the target fixture. If other bathroom groups require "hot water - now" as well, multiple tankless water heaters can be installed. We're seeing more & more installations where two, or more, tankless units are being installed.
Point of use is how these units are used in Europe and Japan. Unfortunately, American houses have too many bathrooms, thus too many target fixtures for this to be practicable. install a recirc pump with sufficient power to overcome the high-head loss through the tankless to trip the burner's trigger. Often voids the tankless warranty & will run it to an early grave by short-cycling the control and burner components. Also generates higher electric bills.
This is expensive, and not just from an energy standpoint. However, the controller on these units is a computer board that really doesn't care if it's cycled 5 times or 50,000 times a year.
I'm more concerned about the heat exchanger, which can lime up, then the burner. The solution to this calcification is a Webstone Isolator that can be purged with CLR on an as needed basis. Another problem with running a circ thru a tankless is the cold water screen. When you push great volumes of water thru a screen, you creat a flow issue when is clogs, another maintenance issue. When dealing with the large system, my solution to recirc and tankless is a variation of Dave's first example. I use one electric wh w/pump, isolated downstream from the tankless wh/whs and throw in another 6 gallon elec wh on another isolate loop w/o recirc pump. This way, when multiple demand is called for, I've got the output of two 3/4" lines to respond to it. Ergo, no flow restrictions in multiple demand mode.
Wow, there is a lot of useful information in this thread, but I'm searching for some opinions.I have a 4000 sq ft slab home with all copper plumbing. The master bath is the farthest from the water heaters, taking between 2 and 3 minutes to get hot water. Since I do not have a dedicated return line and all of the existing plumbing runs under the slab, I'm restricted to the retrofit options that use the cold water return line. I have been considering three options, the Laing AutoCirc1, the Grundfos/Watts, and the RedyTemp. Two of these are single piece units that fit under the sink and one is a two-piece unit with the pump at the water heater and the temp check valve under the sink.Originally, I was planning to install the Grunfos/Watts two-piece unit, but I read some complaints about the hot water feeding into the cold water line when the cold line pressure drops. Now, I'm leaning to one of the undersink models.Any thoughts on which is the better unit with the least side effects?
I have a similar setup at my house with a long wait for hot water in my kitchen. I installed a unit that I purchased at Home Depot. I forget the exact mfr. and model. The pump unit incorporates a timer and a thermostat and hooks into hot and cold lines to the faucet. I insulated both the hot and cold water lines. Yes, there is a minor problem with the cold water being tepid in the summer. But then I can just use the water dispenser in the refrigerator door if I want a cold glass of water. I have had this unit for several years and am very pleased with the results. Beats running two gallons of water every time I want hot water. Roger
I'd find a pro who would be willing to visit your home and explore the potential for running a dedicated line. The flexibility & durability of products, like PEX tubing, might present options that were not feasible just a few years ago. They can also determine if other options, like a small tankless unit to take up the slack, are worthy of consideration.
Barring alternate possibilities, you're limited to what you've mentioned or the installation of a buffer tank if electricity is available near the points of use.
Thanks for the information. I've considered running a dedicated line with PEX and it can be done, but not easily. Given the difficulty of this option, I am exploring the alternatives before choosing to knock holes in walls and fish PEX through my walls & attic. If one the alternatives can reduce the hot water wait time without severe side effects, I'll likely give it a try. If not, this will probably end up on my backlog of projects and I'll continue to deal with delayed hot water.
Most mfgrs of tankless, or on-demand, potable water heaters do not want their unit in the recirc loop and doing so may void the mfgr's warranty. In Rinnai's case, the warranty (so I am told by their rep) is reduced to one year. There are several methods you can utilize to incorporate recirculation and I've included a fairly direct and simple example in the attached drawing. As you can see, the tankless water heater remains completely at rest until a demand-draw is placed on it. The recirc loop can be controlled in any of the manners we've discussed in this thread and does not need to be disabled during hot water use. If you're contemplating the addition of a hydronic load to the mix, there are a number of things to be considered. The first most important issue, in my mind, is maintaining the potability of the water that you and your loved ones will be coming in direct contact during its usage. Bacterial amplification is a concern, so my recommendation is to add a physical barrier between the potable and hydronic systems. Some area codes inspectors or municipal water companies require heat exchangers to be used and they will permit either single- or double-walled heat exchangers. The additional costs are minimal - especially when considering the potential health risks encountered with an "open" system. Here's a good read on using water heaters for boilers: http://www.healthyheating.com/tools/Dave%20Yates%20H20%20vs%20Boiler.pdfAnother consideration will be the heat load. In many cases, the hydronic system's load and the tankless water heater's capacity/modulation are not a good match, which can vastly shorten the life of the tankless water heater. Solar systems designed for generating potable hot water should not be included in the recirc loop without first projecting the solar harvest and excess capacity - if any - at the worst point for capturing solar energy throughout the year and calculating the total Btu heat loss generated during recirculation. For example: I'm capturing just 28,000 Btu's per sunny day in December/January, but I'll be catching 58,000 Btu's per day in June/July/Aug. If excess capacity is generated (perhaps when vacationing), a solar load-shift can be accomplished by pumping into the HX and shifting those Btu's to the hydronic system. A sidewalk or driveway snow-melt system is a great place to load-shift, which is how my solar domestic hot water system is set up to prevent overheating. Solar has many other things to consider, but that's fodder for future articles.
Edited 1/6/2007 5:24 pm ET by PAH
The issue of legionnaires is certainly a very hot topic. The key here is to avoid stagnation of the warm water in a potable loop. The Dave Yates article quoted showed several examples and referenced Dan Holohan's website but skipped over Dan's 24/7 open system pumping scheme which keeps the water flowing in the pipes 24 hours a day and injects hot water as called for by the T-stat. My experience with this system in solar homes with radiant heated slabs has been good but the point is well taken that I risk my customers getting legionnaires and having it be misdiagnosed as common pneumonia. The assertion Mr Yates makes in his article that you would need to have the neighbors come by while you are on summer vacation to run the hot water when feeding the dogs is obviously a red herring, in the summer the stagnant water in the radiant piping poses no more threat than the stagnant water in the cold water piping. It is stagnant hot and lukewarm water that is the risk factor for legionnaires, stagnant cold water poses no risk.
The stagnation issue is also a good reason to use the Grundfos Recirculating hot system as opposed to the Laing pump system as the Grundfos system regulates the velocity of the flow in the recirculating loop but doesn't actually allow it to shut down entirely unless the pump is set on a timer.
I agree that using a small electric water heater is a good and inexpensive alternative to the design I showed using a pump to intermittently circulate water through the Rinnai to keep the water in the tempering tank hot. Both systems are supported by Rinnai's engineering department and detailed on their website and neither system sets the Rinnai in the recirculating loop. However the 8.5 GPM limitation of the Rinnai is not solved by the system you show.
By using a Taco 009 pump and a larger tank you can get short bursts of more than 8.5 gpm out of the combined 8.5 GPM of the Rinnai and the 10 (or more as needed) gallon reserve of the tempering tank. With some of the tower showers or multi generational homes we are seeing it can be very significant to occaisionally up the flow rate beyond 8.5 GPM. This is an inexpensive option compared to adding a second Rinnai and electronic linking controller.
Your excess solar capacity problem is more easily solved IMHO by using a drain-back solar system than by using a closed loop antifreeze system and a shunt load such as you describe, but the drain back system may not be appropriate in your colder climate. We like drain-back systems because we have such a serious problem with overheating here in NC when people take vacations during the hot summer months. And we get hurricanes in the late summer here with extended periods afterwards of sunny days with no electricity to run a pump out to a shunt load.
Thank you for responding to my post. I am aware that open systems, especially staple up open systems, are controversial due to the Legionnaires issue and it is good to have a diologue about the risk factors and when to make the jump to adding a heat exchanger.
Legionella begin thriving at 55F, so yes, cold water can be an issue too. They do best, however, at temps between 80 and 122F with 98.6 considered ideal. Water temps need to be above 133F before the free-roaming colonies begin to die off. System volume and stagnation play a role as well. So do pH and food sources like biofilms, rust and sediment. Incorporating hundreds, or thousands, of feet of horizontal plastic piping (where biofilms and sediment collect) in a hydronic open-system invites a perfect bacterial amplifier to "sit in". The notion that any mechanical device can be added to exercise the hydronic loops or that simply diverting incoming cold water through the hydronic loops ensures safety is a ruse. Pumps & timers fail. If that failure takes place during the warmer months, the occupants won't be aware the system has been stagnant for months.But, as I always suggest: Don't take my word for it - go do your own research on potable hot water systems and bacterial amplification. Seek out hard facts, not hype put forth by those who promote open systems. I've searched for more than five years and have yet to find any credible scientific evidence that supports the notion that an open system will be anything but a perfect breeding ground for bacterial amplification. If, after doing the research, you or anyone else wants to install an open system - have at it! I'm not aware of Dan Holohan promoting any open systems. Constant circulation systems, at least the ones I've heard him speak about or read in what he's written, have always been about closed systems with specific reset controls that, in some cases, will allow a heating system to operate without a room thermostat. If you have a link, post it. Meanwhile, I'll ask him.Your buffer-tank would grant some minimal benefit for drawing in excess of the unit's max rating, but its benefit will be quickly compromised and the customer will be adjusting the faucet to compensate. It's really more like coupling an indirect tank up with a tankless, which can work quite well if the storage tank is sized to meet or exceed maximum draw. I'd be curious to see the numbers for the application you're using this for. Flow rates; adjusted bathing temperature; delivery temp you've set for the Rinnai; the model #; and the coldest water temps you see delivered from the steeet where you live, which averages 45F pretty much anywhere USA. (That info is available via the local water co.) We've utilized larger storage tanks on several occasions in retro-fit applications where an existing ASME storage tank is connected to a large-capacity water heater. Last one was a factory where shift change sees heavy use for showers. The tankless "sees" the storage tank only and is activated by flow generated when the tank's aquastat activates the loop circ. I spent some time with Rinnai's rep last week in a frank in-depth discussion regarding recirc, warranty issues and what they've seen occur in the field. We are the factory authorized service rep for Bradford White in our area & their tankless is made by Rinnai. All tankless water heater brands do a great job - within limitations & all water heaters - tank, tankless, etc. have limitations.
Edited 1/7/2007 7:05 am ET by PAH
I looked it up and you are right. The constant flow system Dan has in his book "Hydronic Radiant Heating" is a closed system. He is not promoting an open system. I really respect what he has to say and would be interested in hearing more about any conversation on the topic you may have with him.The buffer tank is operating as an indirect tank as you mentioned and does need to be sized to meet the anticipated maximum demand depending on the house and the client. It also relieves the cold water sandwich problem which is why Rinnai encourages it's use. Do you feel that recirculating hot water systems for potable hot water are a threat? If legionella begin thriving at 55F why wouldn't they be a problem in every water system in America given that all systems have periods of stagnation? Should we all be washing the sheets to burn up stagnant hot water every time we come home from vacation? I don't do many staple up systems, most of our stuff is solar homes with low temp constant circulation in slab floors. But I do have staple up in my home office and the water sits in it stagnant every summer and I have no indication of any health problems in my family. Just anecdotally I have never heard of a person getting legionairres from an open system. I understand that it is theoretically possible but have you ever heard of it actually happening? Thanks Michael
Dan's reply:Date: Sun, 07 Jan 2007 09:40:29
From: Dan Holohan <[email protected]>
To: [email protected]I don't promote open systems. I'm with you 100% on that issue. He must be thinking about primary-secondary pumping with injection of boiler water into a continuous flow. You may quote me if you'd like.Happy New Year to you all!DanDan Holohan
Dan Holohan Associates, Inc.
DBA HeatingHelp.com
63 N. Oakdale Avenue
Bethpage, NY 11714
800-853-8882
Fax: 516-579-3046
[email protected] Interesting question - re recirc systems and bacterial amplification. If you don't yet have the Watts DVD on Scalding issues, you can get a free copy via their web site wattsreg.com In it, I detail how the entire potable hot water system (Point of Source; Distribution Network; and Points of Use) can be treated to suppress bacterial amplification. However, tankless water heaters present a new issue as they do not maintain temperature. Which brings us back to your question! I don't know. No one seems to know as far as I can determine. That's why I firmly believe total system volume must play a role. Plumbing codes dictate recirc is to be incorporated if the total developed line length exceeds 100'. Yet they also were lobbied strongly enough to permit the installation of an open system! Where's Gallagher when you really need his wry wit?!? So, it's ok to add hundreds of feet of dead legs, yet we're to recirc the potable side. That'd be funny if it wasn't a serious issue (IMHO). Well, people do get LD from potable hot water systems, so it's no stretch to connect the dots - again IMHO. Mark Eatherton, the hydronics columnist for Contractor Magazine recently contracted LD from his own water heater. I have a cousin who suffered the same fate. When you research amplifiers, water heaters are on every list I've seen. Cooling towers get the lion's share of press due to their normally being multiple cases, yet when traced to the source you find the bateria was delivered via the potable water line - most often. Many who contract LD, in fact - most, survive. According to the CDC, 95% of the population has had exposure. However, those who have a compromised immune system or deteriorating health, or an alcoholic, or heavy smoker are more susceptable. If the bacteria are present in sufficient numbers, they can overwhelm the immune system. That's what happened to Mark and my cousin - both healthy individuals, although Mark had a cold at the time. A water heater study was performed quite a few years ago (six studies, in fact) to determine if they had Legionella Sero Group #1 bacteria present in sufficient numbers to obtain a positive culture. In each test group, a percentage of the water heaters were found with colonies large enough to culture and those tests were performed back when water heaters came set for 140F storage temps!So, armed with that knowledge and knowing the newer lower temps of 120F allow more cultures to exist, the last thing you'll find me doing is attaching a system to a potable hot (or cold, for that matter) system that offers the bacteria everything required for rampant breeding! No one knows the threshold level for getting LD because it's entirely dependent upon each individual's current healthg status. So, I chose to err, if it is an err, on the side of caution. My recirc runs 24/7/365 at 140+ leaving and returns to an indirect tank set for 150F with a 10F delta-T. It's my home, so no mix vlv on the outlet (there is one on the 120-Gallon solar tank feeding the indirect as that can get mighty toasty) and ASSE-1016 certified scald-guard devices at the Points of Use. As I'm fast approaching "old-fart" status and with body parts objecting to my 3+ decades in the trade, I've come to appreciate getting old isn't for whimps! We all move to the other side of the lawn, but I'm not willing to give the dude in the hooded robe with his scythe any help if I can help it. Long-winded way of saying I think the majority of residential recirc systems won't harbor enough bacteria to cause great concern. I thought about that for a long time before agreeing to help moderate this discussion.
ThanksI'll stick with the recirculating hot water for potable use as the volume is low and it's getting changed out as people use hot water but I'll re-think using heat exchangers in the radiant floor systems, Those little flat plate exchangers are pretty small and cost effective so that's not really that much of a change in the way I'm doing things. Thanks for keeping the discussion civil, I got attacked at a local gas station by another radiant heat guy who was accusing me of poisoning my family and customers by using open systems. I only do the homes I build, about four a year, but this guy was so upset he couldn't get his words to come out of his mouth straight. Made quite a scene.I've been working on an article for FHB about how to put a recirculating hot water system on a demand water heater and I was aware that I would get some heated letters to the editor if I said anything that was not supportable so I really appreciate having a chance to bounce it around in this forum. I've sent my sketches and article to Rinnai and received some helpful feedback and eventual endorsement. My article about bent steel flitches got at least one flaming letter and I am aware that anything I publish is likely to raise someones ire somewhere. I have one on curved wood ceilings coming up that seems pretty innocuous but you never know. I'd love to send you a copy of my current draft for the recirculating hot on a demand water heater article and get your comments if that would be okay. All the bestMichael
I call it "ages & stages". Others call it reserved civility or patience! Either way, we live in a country where having a diverse opinion shouldn't get you smacked around (verbally or physically) or some of the other much worse fates we see happening around the globe where freedom of speech and independent thinking are restricted. The entire notion of using any kind of water heater in place of a boiler stirs intense passion for many. It was exactly that issue that led me into the bacterial amplification zone. Like many, I too refused to believe what I was reading. But that led me to dig deeper and deeper into the issues. Long & short of it, I found the mountain of evidence all pointed to the conclusions I've drawn. Everyone needs to make their own journey down that path & all I can do is point out the doorway. Down the rabitt hole......... Here's one I wrote for Contractor Mag back in 05 on tankless water heaters. I developed the sizing formula from ones I use to calculate the flow rates when utilizing injection pumping to remote radiant circuits. You're welcome to use whatever fits as long as you note credit in the article:Article submitted to Contractor Magazine from:
Dave Yates
c/o F. W. Behler, Inc.
473 West Market Street
York, PA 17404
Phone: 1-717-843-4920
Fax: 1-717-843-4111
Web: http://www.fwbehler.com
E-mail: [email protected]Approximately 820 words
Serial print and electronic rights as per contract
Copyright: Dave YatesTraining for Tankless Water HeatersBy: Dave YatesLet’s skip right past all the hype you’re seeing in ads for on-demand or tankless water heaters. Walk the aisles of the DIY centers and its there too. “Never Run Out of Hot Water”. Well, that depends on the definition of “hot” and it’s hot water I’m determined to stay out of with my customers, so I developed my own check-list to aid in qualifying any installation for a satisfactory conclusion. 1 – Check the fuel line. This is not your momma’s waster heater! On-demand water heaters operate differently than tank-style units. With vastly higher inputs, gas line sizing quickly becomes an important factor – especially for retrofit applications where even a ¾” feed-line may ultimately need to be replaced in order to ensure proper flow of fuel. CSST piping raises the stakes with higher resistance to flow – use the charts provided by the manufacturer. Under-firing by starving gas flow will return to haunt you. 2 – Venting requirements. Given that you’re now dealing with a direct-vent or indirect-vent appliance (both directly vent exhaust combustion by-products to atmosphere, while direct-vent draws in the air for combustion from the exterior): prevailing wind; windows; doors; and gas meters/regulators become factors for ensuring safe operation. CO (carbon monoxide) is produced by any fossil-fuel-burning appliance, which can be readily drawn in through an open window or door. Local building and national codes govern distance requirements between vent terminations and building openings. Strict compliance is required in order to cover your ####-sets and protect your clients’ health. 3 – BiTe IT and SiT on IT. These units are more technical, require a bit of sleuthing and homework, but offer a greater opportunity for higher profits. Do the math, or take a bath. In order to accurately determine which model best meets your customers’ needs, you’ll need to investigate their use of hot water. Do they use multiple showers at the same time, use them one after another, or, at different times of the day? Are laundry and/or the dishwasher run concurrently? Instead of guessing or relying on literature that claims multiple uses are ok, do the calculations. I use the phrase above to remember the formula. BiTe is the adjusted bathing temperature; IT is the coldest inlet temperature seen during the year (40 F on average throughout the US for municipal systems and 55 F if this is a well-water system); and SiT is the storage temperature. Here’s an example: My customer has adjusted the bathing temperature to 106 F. The storage temperature is 120 F and the coldest inlet temperature will be 40 F. 106 – 40 = 66 and 120 – 40 = 80. Divide 66 ÷ 80 = 0.825 or 82.5%. I now know that 82.5% of the flow must come from the water heater in order to maintain the BiTe. Once my customer adjusts the shower or whirlpool faucet to their desired BiTe temperature, I simply time how long it takes to fill a two-gallon bucket. That gives me the actual flow rate and if that’s 3.5-GPM, then 2.89-GPM must be through the on-demand tank at the SiT temperature. Will the unit meet demand? That’s easy to determine, too, if the appliance efficiency is known. If we’re to raise one gallon of water from 40 to 120 F, that will require 667 net Btu’s be added. 2.89 x 667 = 1,928 net Btu’s per minute or a net hourly output rating of 115,680. If the appliance gross input rating is 199,000 and its rated efficiency is 84%, the net rating will be 167,160 Btu’s – a comfortable margin, but one with just ¾-GPM remaining for an identical BiTe use. Now you can quickly see where that second concurrent shower will adversely affect consumer-expected performance! 4 - Follow the instructions. I’ve been running into a number of on-demand installations where the T&P relief valves are installed on the cold water inlet! Given the fact that we’re required to provide the relief valve, the liability is ours if that’s installed incorrectly or its maximum Btu rating is less than that of the appliance to which it’s connected. Back-draft dampers and venting materials called for in the instructions must be as specified. 5 – Test combustion. If you’re not testing the products of combustion to ensure proper CO, O2 and NOx (nitrous oxides) levels for combustion, you’re exposing yourself to unnecessary liability. You can’t know if you don’t test. 6 – Go forth and sell! Tank-style manufacturers must feel like a prize fighter in the twelfth round of a very bloody fight. First came the FVIR (flame vapor ignition resistance) regulations, then steel import prices rocketed skyward and, following closely behind, insulation had to be beefed up to meet the new energy code, which altered the dimensions of each model. Each change brought with it an increase in costs. The wide variance in price between tank and tankless model water heaters has narrowed to a point where they’re a welcome consideration by consumers. Bent steel flitches? No wonder you got flamed! Not to be ignorant, but what exactly is a flitch and is it contagious? Dan Holohan once told me I'd know I'd arrived when I started getting hate-mail for my articles. They arrived shortly after I started writing and no longer get under my skin, which got a lot thicker. I've been threatened with lawsuits too. I wrote an expose on the home inspection industry that sent one national agency screaming to their lawyers. He sent me some e-mails threatening all manner of things. Made for an interesting episode as I was in CA at the time with the Comfortech Roadshow giving a presentation on r...[Message truncated]
Edited 1/7/2007 12:34 pm ET by PAH
Davere: Will the unit meet demand? That's easy to determine, too, if the appliance efficiency is known. If we're to raise one gallon of water from 40 to 120 F, that will require 667 net Btu's be added. 2.89 x 667 = 1,928 net Btu's per minute or a net hourly output rating of 115,680. If the appliance gross input rating is 199,000 and its rated efficiency is 84%, the net rating will be 167,160 Btu's, a comfortable margin, but one with just 3/4-GPM remaining for an identical BiTe use. Now you can quickly see where that second concurrent shower will adversely affect consumer-expected performance! This is very helpful. I like your BiTe IT and SiT on IT rule. Thanks! As I see it, if my homes are on a well in NC with 55 degree cold water and I'm using the same assumptions as you otherwise, then as I understand your calculations, the maximum yield of 120 degree water from an 84% eff 199,000 Rinnai R-85-I will be 5.14 GPM, not the 8.5 I had been assuming and which had been signed off on by the guys at Rinnai. Am I right on this? Re the open systems it seems to me that the staple up systems which go from 70 to 135 degrees every time they cycle and sit stagnant for long times in the summer are much more at risk for LD than the circulating slab systems that cycle between 70 and 85 degrees and are in constant movement year round except during pump and power failures. So I'll go back to the five staple up jobs I have out there during the coming year and add heat exchangers at no charge to the homeowners before I kill someone. I'll also forthwith start using flat plate exchangers on my radiant jobs, slab and staple-up.A flitch is a type of beam made by sandwiching a flat plate of steel generally 3/8" x 9" x Long between two pieces of wood, generally 2x10's. If you cut and weld the steel into a chevron shape you can make an inexpensive beam that matches the pitch of your roof and eliminates collar ties. It was in FHB last spring. Have a great week, thanks for the great information. Michael
You're welcome! Ain't math cool!?! That old 1-Btu raises 1-Lb of water 1-degree F formula gives us the ability to drill right through any PR hype and get to the truth. Most of that has been toned down by tankless mfgrs and several, Takagi for instance, now provide charts that include real-world performance GPM rates at 120F delivery. Lots of installers got themselves into hot water by blindly following the overzealous claims put forth in literature provided by mfgrs. As you know, consumers almost always lay the blame at the feet of the installer when products don't perform as stated. But gross x eff = net all day every day & the rest falls into place once you know the true mix, delivery, inlet and GPM factors.
It became our task to explain to consumers why replacement water heaters (more than two decades ago) were not providing as much hot water as the older models. When we checked into the problem, we discovered the factory-set temperatures had been lowered to 120F and the Btu inputs had been lowered in an effort to raise operating efficiency and prevent scalding. So, I worked the numbers and discovered why our customers were not happy about GPH production & we started offering an upgrade to 50 instead of replacing a 40 with a 40 & our problems went away. Knowing why this was necessary enabled us to sell consumers the upgrade and slight increase in price. As it turned out, the scalding continues at 120F - more than 100,000 cases each year with several dozen deaths. Hence the Watts DVD was produced to raise awareness and offer a resolution. On average, 35,000 of those scald cases involve children. Our national plumbing codes need to change in order to affect a positive influence for reducing scald-injuries. That info is in the DVD too.
Same goes for our tankless installations. Our customers are given all the factual information we can muster so that there are no surprises regarding how things will work following an installation. The minimum flow rates and that cold-slug you mentioned are part of the introduction during a sales presentation. If they know about things like that and know how to compensate, then we're all on the same page and everyone wins.
My glowcore boiler is dieing. Its rated at 100,000 btu. Can I replace it with a 190,000btu tankless hot waterwater heater such as a tagahi(I am not sure of the spelling) which is also rated for heat use. I have all copper baseboard and two indirect hot water tanks which supply all the hot water for two apartment, and are heated loops from the existing boiler and supply adequate hot water. Is there any reason to go to a more expensive high efficiency boiler.
The Laing or the Grundfos systems will both work. Here are two drawings showing how we put recirc systems on Rinnai's here in NC using the Grundfos system. The "B" system uses the Taco 006 pump with a check valve at the bottom of the tank so all incoming water needs to run through the Rinnai to get to the tank. This limits you to 8.5 GPM output, adequate for most houses. The Taco 006 only spins 2 GPM through the Rinnai when it's running but it only runs when the t-stat on the 10G tank asks for heat. (need to set the tank T-stat 10 degrees colder than the Rinnai or the pump will never shut off) The "C" system uses the Taco 009 pump and no check valve at the bottom of the tank. This is great for houses with big tubs or 3/4" tower shower valves as it can supply short bursts of greater than 8.5 GPM as when taking a shower while filling the jacussi. (again you need to set the tank T-stat 10 degrees colder than the Rinnai or the pump will never shut off)I prefer the Grundfos "comfort valve" system because one pump can pressurize all the hot water lines in a house and the return through the cold or dedicated return lines can be managed by multiple grundfos valves in different bathrooms. I agree that returning the water through the cold pipes is lame because you want the cold water to be COLD, not between 80 and 90 degrees tepid. The threads on the Grundfos valve, while 1/2" will not take teflon tape but must be threaded into a lav supply. It's a bad design and I've been hassling Grundfos about it with no success. so you need to put a stop on your return line and can't just hook it straight to threaded adapters and tie it into the pex. If anybody figures out a work around on this one please tell me. The attached file shows where we tried it and failed, I know you are not supposed to use regular pipe dope up stream of a Rinnai, I was just trying anything I could to get the thing to stop leaking and finally broke the fitting as you can see trying to tighten it. Now we put 12" braided supplies on all four ports and plug the other ends of the supplies, looks ugly but it works.If you want to add a solar hot water pre-heater to the system do not run your recirc through the solar tank, you'll end up using the Rinnai to heat the water in the solar tank as the return water is generally between 80 and 90 degrees. Just set the solar tank between the recirc ststem and the well. But if you hook it up to a radiant floor system do run that return back through the solar tank because that return water is more like 70-75 degrees and you want all the solar BTUs you can to go into your floor to maximize the temperature differential across your solar heat exchanger to optimize output from the solar panels. Hopefully I'll have a piece in FHB soon on this subject that will explain it more clearly. FWIW I'm a licensed plumber and a certified Rinnai installer.Have fun, Michael
i have just installed a bosch 635 es propane 175000 btu tankless. the clients are complaining about the common shortcomings,namely cold water bursts while in the shower and length of time for hot water to reach the furtherest faucet. i checked with bosch for a solution, they suggested a small 10gal electric heater after the tankless hot output.they say this model 635 es cannot have heated water coming in to the input side. i do'nt understand because other manufacturers rannai and noritz suggest your recirculating system thru a flow thru tank to overcome the cold water bursts John Woods in Canada have just produced a 14 and 22 gal flow thru storage tank, with built in thermostat, for this purpose.so my question, would your recirc system work with the bosch 635 es?
I don't believe the Bosch will modulate to accommodate the hooter water coming in. It would tend to over heat the water and might trigger the PT valve if you have one on the out flow (we use pressure only relief valves in our systems) Your best bet (and cheapest) is to put a small electric water heater tank between the Bosch and the house and go ahead and hook it up to the electricity so the water runs through the bosch and then into the electric tank, filling the tank with hot water but using electricity to keep that water hot. The tank will modulate out the cold water sandwich effect. and you can locate the tank close to the first shower and it will keep the water hot nearer to the shower. This is how we did it in the "Goldmine House" on our website. http://www.chandlerdesignbuild.com/indexFull.php?id=goldmine&t=The%20Goldmine%20House
There is one tank in the kitchen for the kitchen and guest bath and another in the laundry closet for the master bedroom wing. The radiant floor runs directly off the demand water heater before either tank. the system has a maximum output of 8.5 GPM but that is plenty for that house and it was a very in expensive solution for a house built for $100/sf.M------------------
"You cannot work hard enough to make up for a sloppy estimate."
The Bosch 635 es has a Pressure Relief Valve on the out flow, what are the other reasons, if any for not modulating the incoming water, which is well water @ around 40 deg winter this would be mixed with the recirc water from the flow through storage tank before it reaches the inflow to the 635 es tankless
The Bosch as I understand it adjusts it's flame based on water flow rate not water temperature (bear in mind that I'm a certified Rinnai installer and have never installed a Bosch water hooter but have worked on the ones others have installed and not been very impressed.) If the return water from your recirc system is coming back at 90 degrees (set point on the Grundfos and Laing recirc systems) the Bosch will check the flow rate and add enough BTUs to bring that flow rate from 50 degrees to 120 as if it was well water, but it's recirc water at 90 so the output temp will be up around 150 degrees. It will work but it's not elegant. The Rinnai, Ruud, and Tagaki systems measure the incoming water temp and flow rate, modulate the flame, and finally pass the outflow water through an internal tempering valve to assure consistent outflow temperatures. And they cost more as a result of this extra consistency and the fact that they play very well with solar thermal preheat and radiant floors. There is really nothing wrong with passing the hot water through one or more little 8 gallon 115 volt hot water tanks before it gets to the shower and the price is very low and electricians and plumbers can grasp the concept very easily and if you place your tempering tanks close to the point of use you get the short wait for hot water with out the energy cost of a recirculating hot system. It's a great low cost alternative if you can live on the maximum GPM throughput of the demand water heater. Its a high value system when initial cost is a critical factor. In higher end houses the Rinnai with a big pump will be more satisfactory due to the higher throughput and more consistent water pressure. We perfessinal plumbers like to install water hooters that have elegance to them don-cha-know.------------------
"You cannot work hard enough to make up for a sloppy estimate."
you wrote
"I don't believe the Bosch will modulate to accommodate the hooter water coming in."
heheheLiberty = Freedom from unjust or undue governmental control.
American Heritage Dictionary
You mentioned that the lines need to be well-insulated. Could you elaborate on how the lines should be insulated? Are you using those standard pipe insulations that one can find at the store? What is the R value?
1/2" fiberglass pipe insul is R-4When asked why is there four engines on a 747------ "cause we couldn't fit six" a Boeing engineer
I'm not ready to buy the water waste claims at face value. 8000 gallons (the lowest estimate) represents 21 gal/day being wasted waiting for hot water to come out of the tap. In my 2400 sq ft home and a lot of others, everyone uses hot water around the same time. The second person taking a shower has hot water instantly. Showering the kids in the evening - same deal. Even then, I'm generally waiting a minute or less for hot. The hot water pipes are insulated in the basement, which also means if anyone has used hot water recently there won't be much wait. I can see where it would be a problem in a very big house though.Pete
Pete,It's good to ask those questions. The only way to determine actual wasted water in gallons, is to capture all of the water until the temp is spot-on for stepping in. We often do that in order to determine sizing requirements for both tank and tankless water heaters, which are based on flow rates, storage temperature for the hot water, highest demand, coldest incoming water temps, duration of draw and percentage of hot water in each gallon exiting the shower head(s).Although US-made shower faucets and heads are virtually all rated at 2.5-GPM, we've discovered many with flow rates much higher - 3.5- to 5-GPM. Stick with the 2.5-GPM though & we're looking at 912.5 gallons wasted for your 1-minute draw each day. While the washing machine won't know it's waiting, hand washing and doing dishes by hand will add to the 912.5, as will other showers/bathing - if onlt to eliminate the cooler water resting ahead of the hot-shot rushing up the line. Gary has some interesting statistics on water temps at start-up and how cold lines affect final delivery temps. As I mentioned in an earlier post, my customers aren't typically calling because they're concerned about wasting water - they want the convienence of having hot water without the wait.
Me either all baths I start the water on full hot and as it fills the tub it goes from cold to hot and then I adjust on the last part of the filling to make it enterable.
Showers for me are about a 30 second wait until it begins to get warm then I am ready to enter, long enough for me to remove my glasses and knock any spiders down the drain.
ANDYSZ2WHY DO I HAVE TO EXPLAIN TO FRIENDS AND FAMILY THAT BEING A SOLE PROPRIETOR IS A REAL JOB?
REMODELER/PUNCHOUT SPECIALIST
I'm with you: selling recirc hot water as an energy/cost saving option is a bit of a stretch, though it is definitely a means to conserve water (which has an energy cost component). If the recirc is by thermosiphon, the heat loss necessary to drive the thermosiphon is not insignificant. Mind you, if you have radiant floors, for half the year all you're doing is re-distributing the heat load between your boiler and your hot water heater so the only energy input is the pump (if you have one). But the opposite is true when you've got to pump that heat back out with an air conditioner- I'd definitely shut down such a system during the hottest months.
>I'd definitely shut down such a system during the hottest months.But that would negate the primary reason people install the system.BTW, I've been in houses that need a COLD water recirc, too! The runs are so long within the house that the cold water tempers, and if you want cold water for drinking, you have to waste gallons. The key to both is insulate, and put some thought into the routing of the lines.
I have a recirc system utilizing a dedicated return line that returns
to the cold water supply on the top of the water heater. My problem is that in
order to have sufficient hot water I have to keep the temp on my
propane hot water heater pegged or the water will not be hot enough.
If I switch off the Grundfos I have gobbs of hot water. This situation
is causing wasted gas as well as eating up my hot water heater. I'm on
my 2nd rod after 2 years wih this system. My friend has a similiar
system but his return comes back to a tee in the drain. Is that my
problem? I have a timer on my system so it runs 6AM to 11PM to give
a rest to the poor hot water heater.DRYDOK
Drydok,Sounds like the dip-tube is either broken or compromised. Standard tank-style water heaters incorporate a tube at the cold-water inlet to direct entering (cold) water to the lower part of the tank. If it's cracked or broken, you'll experience a short-term use of normal-temperature hot water, which will turn luke-warm as the entering cold crosses over and mixes with the exiting hotter water. By cranking up the thermostat, you're setting temp at approximately 160F. If you mix 55F water with that, you'll get something along the lines of 110F (assuming some of the cold is being rejected to the stored water as well).If you disconnect the cold, remove the piping at the tank's inlet, you'll be able to pull (I use my index finger by jamming it into the tube) out the plastic tube. There may be a rubber washer to remove first. Pull out the tube to examine it. If it's broken, that'll be obvious, but if it's cracked, you won't normally see that. Gently twist the tube by gripping both ends - any cracks will open up - just as they do when pressurized by incoming cold water.We install our returns at the drain connection in order to avoid using the dip-tube.The small hole in the first few inches of the dip-tube is not a defect - it's there to serve as a vacuum breaker. New dip tubes can be ordered by make & model. You might find one stocked at the big box stores or local wholesalers & they can be cut shorter if needed. Check your circ for proper direction of flow too, although I doubt that's the problem in this case as its been described by you. And, the thermostat (aquastat), often called a unitrol, may be defective. If that's the case, you might want to replace the water heater if it's more than a few years old. Unitrols are fairly expensive ($100+). Don't forget to turn the temp back down. At 160F, it takes just a few seconds for children and the elderly to get a 3rd-degree burn.
How does his sympton that it has plenty of hot water if the pump is off match up with a broken dip tube?Sounds like something is allowing flow from the cold water supply when hot water is being called for.One good diagnostic is to feel the hot supply line and the recir return line at the WH with the pump running and no hot water being drawn.Then feel them with the only hot water being drawn.If the problem is bypass in the WH because of dip tube problems then the HW line will be much cooler.However, if the problem is backfeed of cold water through the return line then it will be mush colder.
Edited 10/21/2006 12:50 pm by BillHartmann
Convienence is what this is all about. Unfortunately we'll all market it as a water saving feature to help the client feel better about saving pure sparkeling streams from somehow being poured down the drain.
Beer was created so carpenters wouldn't rule the world.
I disappear for a few days and ya'll go off and have a great discussion without me. Sorry I came late to the party but I do have a few opinions to offer.Hot water circulating systems do not save energy ever. They are in fact energy pigs. Many of the points raised previously are valid caveats but in no instance tha I can think of, do they save energy. It is fairly easy to calculate the energy costs. There is a btu loss factor for a given area of pipe with a given r-value of insulation and a given delta T at a given flow rate. It can get a little wordy to calculate it all but in my system the numbers run something close to this if memory serves.130 ft of 3/4" copper with 1" insulation mitered and glued carefully. The calcs at a 3gpm flow and a 50 degree rise with propane as a heat source and a 92% ef heater(rinnai) came to about 20 dollars per month. I currently use mine only 2 hours a day and my total gas bill is 16 dollars a month. It takes about 6 minutes to totally heat the loop from cold. It takes about 2 hours to cool off almost completely after the pump is off. After an hour it is still warm enough for washing hands.The pump expense is about 1 cent per hour or 7.20 per month. This I measured with a killawatt meter. The gas use came from calculations based on tables and charts and guesses based on btu losses done by a mechanical engineer. The actual losses would have to be measured and would be offset by other factors. Let's look at some of those.Some cooling off in the lines happens without a circ loop. The circ loop usually involves additional pipe which increases losses. Radiating from a water heater takes less pipe than looping from manifold to manifold to manifold. In cooling season all of the btus added to the water to aintain the loop are eventually added to the cooling load so you pay to heat it and then pay to cool it. In the heating season this is not the case as it simply reduces the heating load. Some systems are less wasteful than others but the only thing that is saved is water. That may be a significant issue but it pales in comparison to the energy wasted. If you are going to use them, use a timer with an override and teach your family to turn the pump on and more importantly to turn the pump off.I use a Rinnai tankless heater. Tankless heaters and circ loops have a whole new level of complexity related to the way tankless units work. I won't go there now but one thing I do to reduce the waste is to turn the pump off after our morning dishes and showers. I then shave with the water turned on at a flow that is too low to fire the tankless heater. I thereby drain a large fraction of my loop so that the btus are not added to the cooling load and I shave with heated water that would have otherwise cooled in the line instead of heating more water. It's only pennies but all the real savings are achieved pennies at a time.One strategy that I have not used but is applicable to tankless heaters is to have a timer on the pump with an additional intermittent timer inline. When the timer turns on the pump it actually fires the second timer. The second timer always starts with 6 minutes of on time followed by 40 minutes of off time followed by 6 minutes of on and so on. That way the Rinnai heats the line for 6 minutes and then goes idle for 40 minutes unless there is a call for hot water. This reduces the amount of short cycling that occurs with the Rinnai and eliminates the need for a standby heater. I have found aquastats to be totally inadequate to this task. I'll be back later.
Ray,
Did you read my earlier post regarding costs and savings? A more detailed column is out in this month's issue of Contractor Mag and will be available on-line as soon as the web site is updated. Once you've seen it, I'll be happy to debate the merits and cost issues. Properly installed, they do save money.
I read the entire thread before I made my post. I respectfully and completely disagree with you.
That's ok by me. I welcome any point of view and certainly recognize there's always room for mistakes on my part. If I'm wrong, I'd appreciate the help finding out where I turned down the wrong path. However, I'd prefer you use actual facts to back up your stated claims instead of guessing about the results. You must be using a high-wattage circulator in your cost estimate. What watt rating is the pump's motor? What's your electrical rate? Ours are historically high due to getting our power from Three Mile Island. What's the R-value of the insulation you're using? Air temp in the surrounding space where the loop runs? At what temp are you storing the hot water? Well water or municipal? You gave the GPM rate. How'd you get that number? What's the delta-T on your loop? 130' of 3/4". Is that the size for the return too? Is that the entire length? Lots of questions. More to come.Rate you're paying per gallon for the propane? Traditional tank style vented to a chimney, direct vent or tankless water heater? Sorry, I see it's a Rinnai tankless. Which model? That would help explain the use of a high-watt high-head pump. At 3-GPM, there's a significant head-loss through just about any tankless water heater. Where'd you get that 92% eff rating? Edited 10/21/2006 5:54 pm ET by PAH
Edited 10/21/2006 6:11 pm ET by PAH
Taco 009 pump. Rinnai reports the flow rate through it's diagnostics. I said the wattage was reported by my killawatt consumption meter. Our rate is around 12.5 cents per KWh. R-value is 5.6. All of the loop is 3/4" and all is within the conditioned space. Rainwater system uses 1 KWh per 300 gallons. Temp in the tank is 80 in summer and 65 in winter. Loop is operated at 120 degrees f. Delta T would be about 46 degrees in summer and 50 in winter. Price of propane ranges from 1.60 to 1.90 per gallon. The Rinnai is the 190000 btu model. We are a family of three including a 15 year old that lives in the shower for 30 minutes each morning. We entertain often. We use 120 gallons of propane per year including the cooktop, indoor gas grill and the Rinnai. The 92% ef is my memory of the Rinnai rating. It is actually 87%.You can run the numbers but the short answer is there's no such thing as a free lunch. If you maintain a hot loop you will lose energy everytime the heater comes on to maintain the loop temp. The loop will usually be larger than a non loop system and the length of pipe to a fixture is shorter than a complete loop system. The additional loop is additional energy use. I'm tired. Happy computing.Your assumptions of energy savings surpass my total energy cost for hot water both before and after switching to the Rinnai and adding the loop system. Your estimates of wasted water are way too high also. How did you arrive at those figures?
Edited 10/22/2006 1:12 am ET by Ray Moore
Ray,Thanks for getting the info. I'll crunch the numbers later today or this coming week. I'm installing a solar hot water system here at home and have much to do! My "estimates" were based on an assumed loss of water, which was derived from the three web sites listed in an early post and timed water wasted here at home (if my recirc wasn't in place). Their average losses per a family of four were higher. I gauged my numbers on my own home's length of tubing, its volume in gallons and flow rates at shower heads (3). Aren't teenagers fun where hot water use is concerned?!? No wonder you went tankless. Rainwater eh? I'd love to get the details on how you're collecting, storing and treating the water. When I was at ISH in Germany, there were several vendors displaying "regenwasser" collection, storage, treatment and pumping set-ups. Greywater too. I'm planning on adding both as time permits.You're right about the lunch - it's a matter of how much you want to pay for the meal.
Round numbers:
60 gallons per day of hot water
8 pounds per gallon
50 degree rise
30 days per month
propane at 1.80 per gallon
94000 btus per gallon of propaneso away we go:60*8*50*30/94000*1.80=13.78$ per month for hot water. We round to 15$. Natural gas would of course be much less. I speak with many people who report similar gas bills when not using gas for space heat. If you have water saving appliances, how can the cost and imbodied energy of a solar water system ever be justified? When it comes to hot water and saving energy, I sure don't see it as low hanging fruit.
Questions on flow rates:
Can you get me the GPM flow rates at your teen's shower head & yours too. If you can also measure the adjusted bathing temp at the outlets, that will help. Once adjusted for desired temp, holding a two-gallon bucket (or any marked vessel) and timing how long it takes for a gallon of fill. If no marked containers are available, weigh the dry container, run water for one minute while capturing all water and weigh for net weight of water.
You stated the teenager's time is 30-minutes. Times for Mom & Pop?
Not counting lav use as you said it's lower than the required rate for firing. If I should include any at all, you'll need to give me the usage times.
Mechanical dishwasher usage - daily or every other day? Or, if by hand, the approximate gallons used daily. Or a combination of both - like pots/pans/etc washed in sink & remainder loaded into a dishwasher.
How many loads of wash per week? Temp setting?
Edited 10/23/2006 11:06 am ET by PAH
Where to begin?!? First, let me state that what I have to say is not meant as a personal attack, but is a reasoned response to some blanket statements and assertions you’ve made regarding recirculation systems and your own home’s system. My purpose for being here and participating in this thread, is to help educate and give out factual information regarding the article on recirculation. Neither Gary nor I are being paid by FHB and neither of us is selling any of these systems (other than to direct customers where we work, in my case). As a result, we are not biased by material or on-line sales of these systems. As you said, you respectfully disagreed with my (our)positions and I asked you for additional information in order to adequately present you (and the others who visit here) with the facts. I suspect many more read these posts than participate and it's important they be given the most accurate information any of us can muster so that they can study, assimilate, and - ultimately - decide for themselves what may or may not be in their best interest. I hope you view this reply in that light. First, the conclusions:
• Your Rinnai will max out at 5.69 GPM
• The recirculation loop will heat to target temp in 1.17 minutes.
• Daily heat loss for your recirc loop is 42.9 Btu’s
• Pump cost is .02 cents per hour
• Cost to heat water for your home should average $38.04 per monthOK, how’d I get here? Let’s start with the facts you stated:
• 130’ of ¾” copper for supply/return
• 3-GPM with a Taco model 009 pump
• Elec costs at 12.5 cents per kWh
• Running recirc for two hours per day
• Rinnai 180,000 Btu modulating tankless water heater
• Target temp is 120F
• Coldest incoming water temp is 65F
• Propane highest cost was $1.90Propane is rated at 91,800 Btu’s per gallonLet’s start with the Rinnai’s Model 2520 FFU actual GPM flow rates, which modulates from 15,000 to 180,000 Btu’s. Rinnai states this model can achieve 87% efficiency. Although that won’t be true for the entire range of modulation, we’ll leave that at 87% for these calculations. Therefore, the net energy input for heating the water will be 13,050 to 156,600 Btu’s. Designing for design conditions requires I utilize the coldest inlet water temp, which you indicated was 65F. 120F target minus 65F = a 55F rise. Knowing it takes 1-Btu to raise 1-Lb of water 1F, that’s 8.34 x 55 = 458.7 Btu’s required per gallon of flow. 13,050 divided by 458.7 = 28.45 GPH or .47 GPM. At 156,600, the net is 5.69-GPM. 130’ of ¾” copper holds 3.25-gallons. Assuming the Rinnai holds ¼-gallon, the total recirc loop will contain 3.5-gallons of water. On demand, or tankless, water heaters do one thing well – heat water to the target temperature (120F in this case). At 3-GPM (the flow rate you specified), it will take just 1.17-minutes to attain the target temp for the entire loop. From that point going forward, absent any hot water usage, the Rinnai return-water temp will be elevated and the run times will be vastly shortened – short-cycling the unit, which will drive it to an early grave. There are ways to utilize recirc with tankless water heaters that are much better and I'll be happy to write about that for FHB in a future article where we can devote adequate space to spell out the details. The heat loss for well insulated 3/4” copper with 125F water temps, is just .165 Btu per foot per hour (see burnham.com & their Heating Helper booklet pdf file), or 21.45 Btu’s per hour for your 130’ loop. I’m not counting the cool-down as that’s not a fair comparison given that the line would be hot if you did not use recirc. Therefore, just the two-hour stated run-time is allotted for a trotal of 42.9 Btu’s per day. 42.9 x 365 = 15,658.5 divided by 79,866 (propane energy value at 87% eff) = .1961-gallon of propane x $1.90 = just .37-cents of lost energy per year via heat loss in the recirc line. This may not be the energy hog you thought!Let’s examine the pump’s energy costs:
• Taco rates its 009 model as “seeing” 27’ of head at 3-GPM. The potential for erosion-corrosion looms large under these conditions, so good filtration of your rain water is warranted to remove all sediment.
• Standard relief valves for water heaters are rated at 150-PSI. The 009 pump is rated for a max of 125-PSI. The relief valve must be rated for a max of 125-PSI.
• Taco’s tech literature rates this 009 model for 1.4-amps at 115-volts, Using Ohm’s Law, we know that equals 161-watts per hour. 161 x 2 = 322; 322 x 365 = 117,530; 117,530 divided by 1,000 = 117.53 kWh; 117.53 x 12.5 cents a kWh = $14.69 per year, or .04-cents a day in your case, or .02 cents per each hour of run time.Hot water usage assumptions:
• Teen’s shower time = 30-minutes per day
• Mom & Pop – 10-min each per day = 20 min tot
• Dishwasher – 5-min ave per day
• ACW – 3-min ave per dayShowering is a mixed temp. Determining percentage of hot water in showers:
BT (adjusted bathing temp) – coldest inlet temp divided by ST (storage temp) – coldest inlet temp. Looks like this:
110-65 = 45 & 120-65 = 55, so 45 divided by 55 = 82%
82% of flow must come from the 120F water stream.If shower heads are 2.5-GPM:
Teens 30-minutes = 75 x .82 = 61.5-gallons of hot water used
Mom & Pop’s 20-minutes = 50 x .82 = 41-gallons of hot water used
DW = 5 x 1.5 GPM = 7.5-gallons of hot water used
ACW = 3 x 1.5 GPM = 4.5-gallons of hot water used
Daily use of hot water = 114.5-gallons114.5 x 458.7 = 52,521.15 Btu’s per day
Add 42.9 Btu’s for lost energy through the loop’s insulation
Total energy per day for hot water = 52,564.05 Btu’s
Divided by propane net Btu’s = 79,866 Btu’s
Times the $1.90 per gallon fuel cost = $1.2504907 per day
Times 365 = $456.4291
Divided by 12 = $38.04 average cost to heat and recirc per month for propane.
Edited 10/24/2006 9:13 pm ET by PAH
PAH-
Thank you for your thoughtful and time consuming response. I'd like to find out where the disconnects are between your calculations and my measurements.
On closer consideration of my loop length, I think it is actually closer to 200 feet. I think we must also add in the size and volume of each manifold and riser until a heat trap is encountered. These will all be heated by conduction or convection. Not only the water but all the copper and brass fittings and the pump itself are heated as well. This means that losses will occur through any valve that is not insulated.
I can't begin to calculate the heat that is absorbed by all these components on startup. What I can do is turn on the pump and time how long it takes to shut down. That is six minutes. That is a minimum of 1300 btus if we assume a minimum load on the heater which is a big assumption. This is 1500 btus of propane or 3 cents worth of propane.
When the calculated numbers and the measured numbers are not in agreement then I conclude that the input data or the construct of the equation is wrong. If the daily heat loss in my loop was really only 42.9 btus per day that would be an incredible achievement. That means I could heat up the loop, turn off the water heater and still have hot water days later. Doesn't that seem a little suspicious to you? If that were true, then we sure wouldn't have to worry about short cycling the heater.
I will test the cool down of the loop later with a thermometer but after 2 hours I can tell you it is not warm. My loop is well insulated all the way to the valves. The valves, pump and hoffman vent are not insulated. These are measurements, not formulas. This means that most of those 1300 btus have been lost to the interior space, adding to the cooling load in summer and reducing the heating load in winter. The way I see it, the actual losses for a continuously running loop are around 3 cents per hour in propane and just over a penny in electricity.
Oh yeah, I measured the electrical consumption of the pump. As is often the case, the actual running amps and the running amps stated by the manufacturer are not the same. It measures 110 watts. Doing the math, that comes to 1.375 cents per hour. Run continously, that would be $9.90 per month. I'm guessing that you meant 2 cents per hour and not .02 cents per hour. Since we run the pump for only about 2 hours per day, our cost for the pump is about 83 cents per month, let's call it a dollar.
What about the calculation of my gas bill? Once again, measurement trumps calculation. We purchased 174 gallons for the past 16 months. We use propane for the gas cooktop, the indoor gas grill(twice a week) and hot water. I assume that the hot water use is just less than 10 gallons per month. We cook every day. The boy takes 30 minute showers but we ride him about it so it doesn't happen every day. I just measured his shower head flow and got 1.25 GPM. Our shower is 2.5 GPM but our showers are maybe 12 minutes total. We use high efficiency dishwashers and clothes washers.
You calculated out hot water use at 114 gallons per day. I closely monitor our water use because we are on a rainwater collection system and are in a drought. Our total water use is less than 100 gallons per day and that includes some outdoor use to keep the plants alive.
The bottom line for me is that it is misleading to say that circ systems are energy savers. Each system will be different and have different amounts of energy costs associated with them but in no case do they save energy. The amount of energy used to heat the loop compared to the amount of energy used to heat a more direct path to a fixture is a loss. The amount of energy used to maintain the temperature of the line is another loss. The energy to operate the pump is another loss. The total of those losses can be calculated or measured. Of the two methods, measurement is more accurate than calculation due to limitations in obtaining correct input data and possible false assumptions in setting up the equations.
I appreciate the time you have put into posting here. I know it is difficult to find the time to create a meaningful and well written response. You articulate your positions well. I am sorry for my meandering response.
As to your concern about my pressure relief valve and sediment in my water supply, I use a 75 psi pop off valve on my system and my pressure tank ranges between 40 and 63 psi. My filters remove sediment to 5 microns. Do you think this is sufficient?
Thank you for your time and patience with me.
The thing that makes on demand, or tankless, water heaters unique, is their ability to react almost immediately to varying flow conditions (once min flow is established to trigger the burner) and modulate their output to match the target temp. As a result, your water heater will not remain on low fire at 3-GPM from a cold start. Unless Rinnai has hidden info regarding a recirc option that suppresses the firing rate, your water heater will ramp up to 120F and maintain that for the 3-GPM flow rate. Your loop doesn't have enough water for a six-minute firing to hit target temps - unless you're losing a great deal more energy than your stated design holds. At 3-GPM, you will have what's called "plug flow" as that plug of 120F water pistons its way through the circuit.
By the time the water returns to the heater it has lost a great deal of it's energy to heating up the copper and valves and pump etc. That is why it doesn't take only a couple of minutes to shut down. I already said something to that effect. This system is not just the volume of water in x feet of straight pipe.
I think I may have found a problem with your calculation but please correct me if I'm wrong.
On the chart that you referred me to,(great resource by the way) on page 49 it states that the loss per linear foot per hour per degree f. delta T is .165 btus. This chart assumes 75 degree surrounding air. I think you forgot to factor in the delta T. This means your conclusion is off by a factor of 50. The actual loss would be .165*130*2*50=2145btus per 2 hour period. 2145*365=782925 divided by 79,866 (propane energy value at 87% eff) = 9.8 gallons of propane x $1.90 = 18.62 dollars per year.
Let's remember that the loop adds length and therefore loss to the system.
Let's look at the same system run continuously and figuring in the losses related to the fixtures, pump and manifolds. We'll assume an equivalent pipe length of 250 feet. Remember the fixtures and pump and check valve and hoffman vent are not insulated. The EPL might be longer. Based on these assumptions however the numbers run like this.
.165*250*24*50*365=18,067,500 btus per year.
In dollars that's 18,067,500/79,866=226.22 gallons of propane * $1.90 = $429.82
That is the kind of energy hog that a circ system can be. It can actually be much worse if it is not properly installed and insulated.
In my system the losses can be figured by the btus to heat the entire loop and the btu loss per hour to maintain the loop minus the loss that would have occured in the short run to the individual fixtures. It is much less than the losses for running it continuously.
Two additional points. My last two clients claimed to care about energy consumption but in fact run their systems continuously because they don't want to be bothered by the timer and the off chance that they may want hot water at 2 in the morning. Also consider that most loops are only insulated with 3/8" insulation that dramatically increases losses and is not glued at the joints. Even good plumbers will tell you that the increased cost is not recoverable. Obviously it is the best insulation dollar you can spend.
Hot water circulation systems save water and waste energy.
Accckkkk! God, I hate making dumb mistakes. Good catch Ray. That's what I get for burning the midnight oil and rushing through an issue. I completely missed that note.
OK, you're at $18.62 per year. I can't agree to the consideration of this as a typical recirc system that's being run 24/7/365 though, as it's not a very good design and certainly qualifies as an energy hog. In fact, it's compromised the Rinnai's warranty and may well have voided it completely. See: http://www.rinnai.us/media/Warranty_water_heaters.pdf
If, on the other hand, you want to consider a properly sized pump and return line, we can whip that horse. However, you'll be limited to considering a system that is approved by Rinnai as outlined in the link above. Or, we can move on to considering systems that do not have the same restrictions.
As for the "heating up" of the line and its components, hydronic designs (it's being run just like a hydronic heating system) utilize a 15% pick-up factor to account for heating up the components. At .025 gallons per foot for 3/4" copper tubing, you'd need a heck of a run for that Rinnai to take six minutes to end its first cycle.
So, if we now bump up your total lineage to 250' per your suggestion, you've got 6.25-gallons of required energy. Divide by 3-GPM & multiply by 1.15 to get 2.4-minutes.
As for Taco's technical literature and your watt-meter? I've worked with the owner and their R&D team and I trust their information. I'll stick with what they have listed for amps at 115-volts and Ohm's Law for determining the watts.
Edited 10/25/2006 5:09 pm ET by PAH
pah..... thanks for all of the posts so far... i love reading over you guys shoulders
anyways.. here's the situation
have a master bath, 2d floor bath & lavette at one end of a house
and the boiler-mate & oil fired boiler at the other end of the house ... about 50' run for the first floor & say 70' run for the 2d floor
the main feed is 3/4 pex uninsulated... the basement is totally insulated but not heated... probably an ambient temp of 60 deg druing the heating season.. maybe a little higher
customer complains that doesn't want to wait for hot water
my response is ..... why not ? what can possibly be done to this system that would make sense.... insulating the line will not change this wait time.....
a recirc system will ... but the expense doesn't make any sense to me ( but it's not my money )
the plumber is inclined to install a by-pass system and use the cold water supply as recirc..
but again.... to me... not the customer, this doesn't seem to make a lot of sense either...
what am i missing ? my inclination ( ie: if it were my house ) would be... run the water.. but perhaps it's just my life style... we only use the hot water in the master bath in the morning, so it's a once a day , one shot deal... with maybe an evening shower 3 -4 times a week
what would you recommend to the homeowner ?Mike Smith Rhode Island : Design / Build / Repair / Restore
Mike,Options, we got options! Get your red hot options......Now there's a sales opportunity. Inconvienence, desire and money all rolled up in one. Tis why some folks drive Mercedes while others are content in a Yugo. As you noted: It's not your money! As a contractor, that was a hurdle it took me years to get over. So many times I left money on-the-table because I couldn't afford, or see the value of, options others presented - and got the sale. It eventually dawned on me that it wasn't my money and, therefore, it wasn't up to me to decide what my customers could afford. What I'd do? Quickly jot down ever option you can think of & do that in no particular order - anywhere on the page & at any angle is just fine. Once you can't think of any more options, organize the list by circling best-to-worst and create an ordered list. From that, begin building your proposal like a menu with tantalizing tidbits about each "meal". You're selling the sizzle, not the steak. You can list a tankless to handle the pick-up load, an electric buffer tank, under-counter electric water heater, any of the recirc options listed previously and/or whatever the customer(s) give you clues about during your Q&A with them. Pay attention to what the wife says, her body language, and be sure to listen actively by giving her feedback that lets her know you heard and understood her needs. Meanwhile, give the husband his due and let him think he's making the decisions. If she really wants that Mercedes, she'll let him know which model they'll be driving. The best part is that by letting them both know you're actively listening and asking questions, you will no longer have any competition; the cost will no longer be the main focus; and you'll be the winner. You're dealing with a nice-to-have convienence item, not a must-have, and that typically leads to a higher profit margin. Same reasons why folks will pay $1,800.00 for a toilet seat that washes their behinds with warmed water!
This system was installed to Rinnai specifications 3 years ago. Their specs have since changed due to their ignitor failures. Their current call for an electric water heater to keep the loop hot is pretty silly and kills three of the best reasons to use a Rinnai.
1 It is an expensive source of hot water.
2 It requires a ptr and drain pan inside the house
3 It limits the temp setting to one level. If you set the electric loop heater at 110 and the Rinnai at 120, it works fine. Change the Rinnai setting and the system will not perform as designed.
You seem to not like tankless heaters. They are problematic with loops but the problems are not insurmountable. My gas bill speaks for the efficiency of my loop and my Rinnai heater.
Limiting the run time of the pump is a good way of solving the ignitor issues and the excessive losses suffered by circ loops.
Can you educate me about better ways to run loops with and without a tankless heater?
As to the pump wattage, motor manufacturers routinely rate their pumps at the top end or above the average running amps. The motors are built in batches and test in a wide range. They don't have warranty issues with pumps that run at lower than rated amps but higher than rated amps would indicate a problem. Have you tested this pump or similar ones?
"As to the pump wattage, motor manufacturers routinely rate their pumps at the top end or above the average running amps. The motors are built in batches and test in a wide range. T"A motor should not have that much of a range.However, the motor is just driving a pump, converting electrical energy into mechanical energy.That there are LARGE VARIATIONS in the loop in which that pump is installed.That current rating is for the whatever point on the pressure flow curve the pump is speced for.
First of all, I love tankless water heaters - under the right circumstances: a little candle-light; a glass of wine; and a romantic moonlit dinner! Seriously, they can be the greatest thing since sliced bread - if the upfront homework that's required points in their direction. They are not anything like the types of water heaters we were raised on and I see too many botched installations - by both homeowners and mechanical contractors. I do a fair amount of consulting work to unravel tangled mechanical messes. I can educate you on the right ways (there are many) to treat tankless systems, but there's a limit to what I'm willing to do for free for FHB. I agreed to help on this recirc issue for a number of reasons. If you survey what I've written for Contractor Magazine, you'll begin to understand my motivation. I'm more than willing to delve deeper into the tankless issue, but that's entirely up the the editors at FHB. Your set-up must be a black-hole where energy loss is concerned. There's no on-the-surface explanation for that six-minute lag. Johnny White is a good friend and one hell of a straight shooter. The men & women who work with him at Taco are a breed apart in our industry and some of the best folks I've ever had the honor of working with. I've been to Cranston, RI several times and spent a day with R&D the last time I was asked to visit. They have vision while many others are blind! I have full confidence in them, their products and the tech lit they have available. I've been using their products for decades without ever once experiencing a problem. When I have had technical questions, they went overboard to resolve the issue(s) and/or help me with design work. They're an American company that promotes from within and they offer college accredited courses in-house for their employees. Johnny takes the stewardship of Taco seriously, as he must, because he is up against stiff competition from European mfgrs. That keeps Taco lean, but not mean, as they bust their butts to remain at the cutting edge of technology & at the edge they are. Their integrity is beyond measure & that's just one reason why I trust their literature on the 009. We work within a trade where loyalty is a fickle maiden. If Taco, or any other company, were found to be fudging the numbers, we, as hydronic contractors, would abandon them in droves. Do we also use other mfgrs products? Absolutely. I strive to use most of what's available & that includes tankless water heaters. My test equipment is nowhere as sophisticated as what I find at Taco, Grundfos, Armstrong, Wilo, or B&G - to name just a few circ mfgrs. My hand-helds are mere toys by comparison.
Ray
All the major tankless manufacturers are getting on the bandwagon that advocates using a small electric water heater as the source of heat for recirc lines on their heaters. Some have even lowered the warranty to 3 years if one of their units is installed with a recirc hooked directly up to it. As for energy usage, I agree, it is less efficient. But, it cuts way down on unit maintenance. It also decreases velocity in the recirc line because you can use a 1/25 hp pump instead of a 1/12 hp pump required to achieve sufficient flow thru the heat exchanger to make it fire. As for the increase in installation costs, the people I sell these systems to don't seem to be the type who worry about price points.
I just measured my loop warm up cycle and got 3 minutes and 10 seconds. After being off for 6 hours, the temp of the hot water line was the same as the cold water line at 70 degrees.
I will time the warmup cycle again in the morning.
Aloha,
I have been through all these posts (I think), and find none that mention a solar hot water system. Here in sunny Hawaii, that is the only method we use to heat our water...never need a backup, though we have one just in case. Thus, if we retrofit our system to dump cold water from the hot water pipes back into the hot water system, I am not sure how we would reheat the water. Will it flow back through the solar system and be reheated by the sun? Pardon my ignorance, most of these posts are way over my head. I just want to save water; our current system wastes lots while we wait for hot water. Since our hot water heating is free, we don't worry about heat loss while the water sits in the pipes.
Also, is there anyone out there in Hawaii (Oahu) who is an expert on this? If so, I may have a job for you! Thanks for any guidance you can provide.
diamondhead
> Thus, if we retrofit our system to dump cold water from the hot water
> pipes back into the hot water system, I am not sure how we would
> reheat the water.These systems work by constantly pumping hot water from the tank through the lines and back into the tank. Although there are some heat losses in the system, one way to look at it is that there is never any cold water in the pipes. You'll be dumping hot water back into the tank. You also want to insulate the circulation plumbing to keep those losses to a minimum.All I know is what I've read.George Patterson, Patterson Handyman Service
OK, I'm officially jealous of your living in such a beautiful spot! Can't wait to return one day.We too are utilizing solar. Ours is a 30-tube array with 120-gallon storage. However, in PA we don't get nearly the solar insolation you do and we do use our back-up. I currently have 24/7/365 gravity circulation attached to the back-up, which is an indirect water heater fed energy from a modulating condensing hi-eff boiler. Were we to rely strictly on solar, my recirc would be either timed or an on-demand system. Are you using a roof-mounted tank? I noticed quite a few homes in Hawaii set up with rooftop packages. If you decide on constant recirc and discover the heat losses are greater than expected, you can always add a timer or on-demand controls after-the-fact.
Dave
Are you familiar with Gary's article "Benefits of Demand-Controlled Pumping" in Home Energy Magazine? Knowing your concern for the dangers of Legionaire's Disease, I'd be interested in what you thing about pumping hot water back into the cold side of a house water system, assuming hot temperatures of less then 140ºF.
Scott Denny
Lunch break! After lunch I'm ready to attach my new roof jacks while harnesed and tied off to my truck on the other side. At 36 degrees, I'm not comfy walking on shingles 45' above the earth.Ahhhhhhhhhhh, now there's a can of worms. I wondered if this would come up. My position on bacterial amplification is pretty firm and fairly well known. That's why I have a dedicated return that circulates 24/7 and I maintain my storage temp at 140F and above. (140F min to 155F max via the aquastat programming in my Vision 1 control.) The problems are there - without the cross-over, so the issue is slightly magnified in my mind. Until plumbing codes change, the issues will remain as they are.
If your storage is at 140ºF, I hope you have a tempering valve on the loop. If so, what brand do you use? I've been reading about Caleffi and was wondering if their 1017 is any better at resisting mineral buildup than the domestic models.
Watts. That plus ASSE-1016 certified scald guard units at points of use where humans can contact hot water. Goofing off tonight, I clocked my recirc line's flow with all insulation removed. The line was off for most of the day, so it was at room temp for hours prior to the test. Took 32 minutes to travel the 74' of 1" and just under 10 minutes to travel the 79' of 1/2".Took 2 full minutes to get adjusted temp at the shower.
Dave
You ought to ask Gary for a copy of his "Water, Some Like It Hot". I got mine a week and a half ago at a seminar in San Jose which I didn't attend. Aligators were catching up to me that day, so I had to leave half way thru the morning seminar "Tankless Water Heaters" lead by David Springer (who says he's met you) and had to miss Gary's afternoon class.
Hail well met! Yes, enjoyed the encounter with David.Turned out that Gary & I were both speaking at ISH-NA in Chicago a few weeks ago - at the same time & we missed each other as a result. Gary forwarded a number of his articles. Soon as I get the time.........
Edited 10/22/2006 9:14 pm ET by PAH
Gary
Has anyone done any studies on the energy costs of supplying domestic hot water by tankless WH compared to a modulating combi boiler and indirect hot water tank setup?
Scott Denny
Sorry for the long absense.
Scott: I have not seen such a comparison. The relative efficiency calcuations seem straightforward, however, I would also want such a study to look at how well the different options meet the customer's desires for hot water. All the best. Gary
Ray
Your statement, "you can run the numbers but the short answer is there's no such thing as a free lunch. If you maintain a hot loop you will lose energy everytime the heater comes on to maintain the loop temp," is accurate for a tankless WH. However, water loss and irritation at having to wait for how water have to be taken into consideration. That's why the Japanese them as point of use appliances. BTW: You wouldn't be an engineer by any chance?
Scott Denny
BillGood question! A brain teaser to be sure.I don't know which model Grundfos pump is being used, but his post tells me there's a check valve in the recirc line (or in the pump if it's an IFC model) due to the "gobbs" of hot water when the pump is off. Absent a check, the opposite would be more likely due to reverse flow of cold up the return. And, with the check installed in the correct direction of recirc flow, he can't be pumping the wrong direction. When his potable water system is at rest, no cold water can be added to the system's tubing (or subtracted either). It's obviously moving as he's seeing a mixed temp during a draw. No mention of a wait, so I'm also assuming he's connected to the hot close to the point of use. If he was inadvertantly connected to a cold line for the return, he'd not likely see any affect with the pump on or off. There's a lot of merit to the cross-connection theory expressed by plumbbill. If the Grundfos has sufficient pumping power (and many will), a cross-connection like the solenoid valve in automatic clothes washers can be defective and permit a second mix-point during the draw. But, a cracked dip-tube can be the source too. Wet rotor pumps generate a fairly steep pressure drop, which induces water to move in a closed circuit. It's possible the pump can exert more line pressure differential that the actual draw. Add them both together and there might well be an added increase, which could spread a crack in a dip-tube wider. During recirc flow, a defective unitrol could see warm enough temps to prevent the burner from cycling as it would if the stagnant no-flow storage permitted stratification and the unitrol "saw" the colder layer. A system line drawing would be helpful. On it, pipe sizing, insulation type and pump model should be noted.
Edited 10/21/2006 2:42 pm ET by PAH
There's a lot of merit to the cross-connection theory expressed by plumbbill. If the Grundfos has sufficient pumping power (and many will), a cross-connection like the solenoid valve in automatic clothes washers can be defective and permit a second mix-point during the draw.
Also a shower valve that has seperate volume & temp controls.
If the mixing valve is before the volume control you have a constant supply on both sides if you have a check valve failure or missing----- that good ole path of least resistance rears it's ugly head.When asked why is there four engines on a 747------ "cause we couldn't fit six" a Boeing engineer
That should be easy to check. Turn the mixing valve to straight cold. Turn on the volume control. If you get warm or hot water, check the check valve.
Agreed! Just added that to the drawing from this morning I did in MS Paint to follow the water. We've used them at times for scald-guard protection with non-ASSE 1016 faucets. With the recirc pump on, there is a tug at the hot inlet side of the mix valve. If it has a defective check-stop, reverse fllow can occur there too.We once chased a ghostly cross-connection that was causing the cold to get hot during odd intermittent times. None of the usual culprits were found to be the cause. So, I basically camped out to be there when it happened. The single-lever kitchen sink faucet's cartridge, as it turned out, would occasionally allow natural gravity circulation without a single drop from its spout and it would vibrate slightly as the spring-checks rapidly open/closed. Sorry about digressing - your post brought back the memory!
PAH gave an excellent answer.
I'm going to add a small part.
If you shut off the cold water valve feeding your water heater, then open a hot valve somewhere to release the pressure.
With the pump power off loosen the flange on the inlet side of the pump, if you get water comming out of that( other than a standard dribble of residual water in pipe)
You either have your "dedicated" circ connected to a cold pipe, or you have a mixing valve somwhere that has a check valve failure.When asked why is there four engines on a 747------ "cause we couldn't fit six" a Boeing engineer
plumbbill,
Thank you so much for your diagnostics. I'm out of town for a while
but I'll check it out and return to the group.drydok
PAH,
Thank you for your help on my recirc system. I'll check it out and
return.drydok(34)
See message 34. It was directed to me in error. I'm no expert in this field.BillEdited to add: I see you already got it. Great thread!
Edited 10/21/2006 9:50 pm by BillBrennen
You need to install a one-way swing check valve on the return line
I have a check valve in the return line.Thanks for the help.
DRYDOK
Maybe the check valve is stuck in the open position? They do that sometimes. I always thought that when it happened on one of my installs it was because of bad Karma. To be truthful, its because of mineral buildup in the check valve. This condition can effect both swing and spring check valves.
Drydock and others,
We have an identical issue with our new HW recirc. system. Our HW (natural gas) thermostat has to be set much higher when we are using the recirc pump. If we shut the recirc. off, we also have "gobs" of hot water, too close to the scald situation for our comfort (we do set the thermostat back at this point).
Our pump runs from 6 am to 11 pm also. I have come up with a different theory, after months of operation and checking temp's of incoming/outgoing water.
I have 2 other circ pumps using the same (oversize) NG water heater; a floor heat system, and a hot water furnace. We don't have this problem using these 2 systems, but I note that the returning "cooled" water from these systems is much, much cooler than the outgoing hot water.
With the HW recirc. system, however, the returning "cold" side water is almost identical temp. to the ougoing hot water.
Now the THEORY. Is it possible that I am returning very hot water, continuously, to the bottom (cold water area) of my HW tank, where I presume the thermostat is located to sense incoming cold water? If so, am I tricking the HW tank into thinking it rarely has to turn on the heat? I suspect I no longer have a temp. stratified water tank, as long as my HW recirc. pump is running.
Turn off the recirc., and presto, everything is back to normal.
Notes: all circ pumps are fed into the cold water inlet at the top of the tank, and all lines have check valves. HW tank is 3, 4 years old.
Interim solution for me is to install a timer or some thermostatically controlled timer for the HW recirc pump, to allow some time for the water in the HW tank to "stratify" again.
Any suggestions? I haven't sold my Heating/Cooling service man on this one yet.
Ken
Check to confirm the direction of pump installation. Make sure it is pumping towards the heater.There is only one planet earth. How many chances do you think we get with her?
Think it's possible that his pump is creating too high a flow rate? If he's returning hot water, then it's certainly circulating more than it needs to. I'm curious on his flow rate vs a thermosiphon setup (in a place where that's appropriate).
Same thought here. A pump model/brand and pipe sizing along with total developed length would help to determine what's going on within the system. An oversized pump could produce the results as described.
Thanks for the post. I'm visiting in Calgary at the moment, but as soon as I return to Ontario, I'll post the specs on my system. All I have for now is that my pump is a Grundfos, and I am certain that I am returning too much, very hot water to the HW tank.
Can anyone point me to some info on thermosiphoning? New one for me.
Appreciated.
Ken
Thermosiphoning is a passive system that works with multi-story houses. Normal supply, narrower recirc line, hot water rises and forces circulation.
Here's an article describing the thermosiphon process:
http://www.contractormag.com/articles/column.cfm?columnid=62
Couple of questions arise from the thermosiphoning article:
1) Can I leave my circ pump (unplugged) in-line while I experiment with the small hole in the check valve, or will the idle pump rotor have a negative effect on the system?
2) I originally installed the check valve because I was drawing cold water up the return line when the shower etc. was used outside the hours of pump operation. Will I have this negative effect again, or is the hole in the check valve too small to make an appreciable difference?
3)I am installing a HW towel heater in the line at approx. the point where my dedicated return line starts. It will have a 5 foot drop to the towel heater, and adds about 10 feet plus to my system. Would this addition be ok with thermosiphoning, or better to stick with a properly sized/timed circ. pump?
Current rough specs as I am not at home: Grundfos circ. pump, first 30 feet of loop is 3/4" copper, switches to 1/2'' copper for 11 feet through old section of house, then switches to 1/" PEX for the 41 feet of return line. Feeds into cold water inlet, as do my other two circ. pumps (floor heat, air handler, all with check valves).
Much appreciated. Ken
OK, now I'm officially concerned! Let's move through the questions & I'll give you my reasons for the concerns.
#1 - Yes, providing it's not an IFC model (Internal Flow Check), which it can't be if you had reverse flow issues. Just as that cold water backed up the line, warm water can flow by gravity in the right direction.
#2 - No, the hole is small enough that the cold-water mini-injection via that hole won't be noticed.
#3 - Might be. I'd need to see a drawing. But here's where I begin to get nervous about potable hot water systems, the volume and temperature relationships along with volume.
If I understand your post correctly, you have a hydro-air unit and radiant floor circuits tied onto this same water heater - without a physical barrier to keep the potable water separated from the hydronic systems? If so, do yourself a huge favor and Google "water heaters + bacterial amplification". I've studied this issue for several years and believe open systems are, by their very nature, a perfect bacterial amplifier. Legionella Sero Group #1 (the nasty strain that causes Legionaires' Disease) bacteria are quite commonly found in potable water systems - in low culture numbers. They need just a few things to begin rampant culture growth: water temps between 55F and 133F with the ideal range being 85 to 122F and 98.6F being absolutely perfect; pH between 5.5 and 8.0 - virtually all potable water systems in the US; a food source, which they get via biofilms, sediment and rust in tanks and long stretches of horizontal tubing (there's the radiant thing); and stagnation - any time the system stops flowing. System volume plays a role too. Don't take my word for it though - reasearch & learn on your own. Google's a great place to start.
You'll also find a number of articles I've written at Contractormag.com regarding this issue and a pdf on "The Great Water Heater Debate" at healthyheating.com - their most downloaded pdf file according to Robert Bean.
One typo error in previous post. Should be, switches to 1/2" PEX for return line.
Ken
Sounds like a great theory to me. I think we have the same systems,
we certainly have the same problem. My HVAC guy seems to think if
the return comes in at the drain rather than the top it will solve all.
I don't know. I also didn't bring into the forum the fact that I have
an oil fired boiler with a domestic hot water coil. I only run this in the winter & I have the capability to exclude it from the system when the boliler is shut down. However, in winter it does not change my water
temp. problem which makes me think that maybe you're on to something.
By the way how do you check the temp of your incoming water.
Thank you very much,
Drydok
Drydock,
Good to hear from you. No one in my area has a similar problem, and I wasn't receiving much attention when I tried to explain the issue. Any answers I rec'd seemed to be pretty much try this and if it doesn't work, try something else.
Anyway, I have only been checking water temp in the pipes by hand, but I'm lucky enough in that the pipes are close to each other. I can put on hand on the hot side, and the other hand on the return (cool) side for all 3 circ. systems.
For the floor heat and heat exchanger, temp. difference is quite pronounced, but for my HW heat recirc. system, I couldn't really tell if there is any temp. difference between the hot and cold sides.
Someday, we may get to the bottom of this.
Thanks,
Ken
Athomemom I intend to work on this over Xmas holiday so keep in touch.
I'll let you know if I discover anything.
Drydok
Tacp makes a time and clip on aquastat for exactly that purpose. Online the aquastat is about twenty dollars and the timer is about ninety. Or use one central timer and aquastats at each circulator
This is new info for me. Could you give me some more info on tacp, so that I can research this further?
Appreciated,
Ken
here you go.......taco-hvac.com
I had a recirc system recently installed at a customer house along with another heater in parallel and the plumber had a dedicated line to push hot water to the farthest fixture with the pump installed at the water heater via a tee off the drains which was not working properly and the customers complained from day one about running out of water after many discussions with my bullheaded plumber my heating contractor fixed the problem in five minutes by reversing the direction of the water flow it seems when the customers used hot water and the tank would start to refill the recirc pump would pump 38 degree water through the system cooling our $1800 parallel recirc system and was worse of a system than they originally had.
Hello all,
Just a few questions on domestic hot water recirculating system. Our building 13 years old and we have experienced several leaks in the copper tubing of the hot water recirculating system.
The circulating pump is a grundfos UP15-18 SF. The output of the pump is in 3/4'' copper tubing to the 75 gallon water heater. Then from the water heater there are 3 supply lines of 1'' that run in different direction of the building. The 3 supply lines at some point are reduced eventually to the 1/2'' return lines that all connect on the same 3/4'' line at the input of the pump. The building is religious monastery of 40' x 100' with 3 stories.
Over the years, we had several water leaks in the 90 degree elbows and tees on the 1/2'' return lines before they connect to the 3/4'' line. We installed a bypass on the pump to slow down the flow of water in the supply lines since we thought that there might be a corrosion problem due to the high velocity of water and the fast changes of the water flow. Even with a portion of the flow going through the bypass of the pump we still got some leaks in the return lines.
Does anyone know if this is a problem due a bad design? Should the return piping be 3/4''? Would it help to install a smaller pump? Will a smaller pump give enough head to the system? Our water pH is 7.4 so I don't think acidity is a problem.
Kind regards,
Luc
Just a few questions on domestic hot water recirculating system. Our building 13 years old and we have experienced several leaks in the copper tubing of the hot water recirculating system.
The circulating pump is a grundfos UP15-18 SF. The output of the pump is in 3/4'' copper tubing to the 75 gallon water heater. Then from the water heater there are 3 supply lines of 1'' that run in different direction of the building. The 3 supply lines at some point are reduced eventually to the 1/2'' return lines that all connect on the same 3/4'' line at the input of the pump. The building is religious monastery of 40' x 100' with 3 stories.
Over the years, we had several water leaks in the 90 degree elbows and tees on the 1/2'' return lines before they connect to the 3/4'' line. We installed a bypass on the pump to slow down the flow of water in the supply lines since we thought that there might be a corrosion problem due to the high velocity of water and the fast changes of the water flow. Even with a portion of the flow going through the bypass of the pump we still got some leaks in the return lines.
Does anyone know if this is a problem due a bad design? Should the return piping be 3/4''? Would it help to install a smaller pump? Will a smaller pump give enough head to the system? Our water pH is 7.4 so I don't think acidity is a problem.
Luc-
If you are saying that your 90 degree elbows are wearing out due to high velocity in the 1/2" pipe (don't know if it could or could not do that, but generally in piping systems this can, if you are using the thinner gage of copper piping, that would make it worse. You want the "blue" piping).
Anyways, I put a hot water recirc system in a two flat that I own last year, it has two branches of hot water, and they are 3/4" supply and 1/2" return for the hot water recirc.
I DO NOT HAVE A PUMP and it works FANTASTIC! I have about 15' of elevation change from the water heater to the return.....all you need is a check valve on the return of each branch in the horizontal position to block reverse flow.
That will solve your problems once and for all most likely.
I would like to make two observations and would like any feed back for solutions.
ONE:
Where I live now, we are are in a 2200 sqft single story track home. The ceilings are insulated to R38 aand all supply lines are run across the top of the ceiling joists (truss). The home is PEX and their is a manfold and each fixture is a home run. So we have hot supply hot lines running to each bath( tub, 2sinks and shower) and 1 to the laundry and one to the kitchen. This kitchen supply tees off under the sink to the dish washer. If I shave in one sink I have to wait for hat. The wife has to wait for hot in the other sink unless we play leap frog. The same is for the shower. This seems to be the norm right now at least in this area of Central Calif.
The only way to make our system work is to put a point of use at each fixture and this is impossible at the tubs and showers. Not very cost effective. Any solutions for this type of sysytem where you have home runs for each fixture?
TWO:
Well, as some others have suggested, I didn't see the cost savings over water use oon our last home in Washington Coast. Propane was over $2.50 gal and our city had the highest water rates in the state.
We were using a propane feed 40 gal water heater. The efficiency was quite high, but I don't remember how much. The recirc pump was a Taco and was hooked up correctly and the sysytem worked GREAT.
The problem was that the waste of propane was quite high, even though we had the pump running on a timer, mainly morning and evening. Never turned on form 10pm to 6am.
I later turned off the recirc sysytem and the propane comsumption was greatly reduced. I did a quick calcution and the energy waste did not compensate for the water waste.
In the end, I turned on the system becasue I wanted the comfort and was willing to pay for it. Personally this is the reason why most people want them.
No wonder you've got a migraine! The wait is a pain. <!----><!----><!---->
When we do a home-run system like yours, we pipe just one hot line to a double vanity. Given that lav faucets are set to flow 1-GPM these days, a single PEX line works very well without any noticeable pressure-drop or flow-loss issues. That's providing the installer checks the flow chart against the elevation change and length of the run for the water line material used. You can cap off one of the two and sister the connections together inside the vanity cabinet(s). Once done, an on-demand pump could be added there or back at the manifold with a cross-connection. If the lines are accessible from the basement, a dedicated return can be added. <!----><!---->
I've also seen (because of temp issues) an application where a recirc pump was added with flow-check at the main supply ports of a manifold with spring-loaded checks installed at cross-over points to serve multiple points of use. There were several cold lines that became hot (same temp as the water heater storage), which was not safe or acceptable for the homeowners. Had the installer used thermal-checks to limit the warmth of the cold "returns", that could have worked. However, if we know in advance that recirc is wanted, we'll oversize the hot line to the bathroom (master bath normally), install T's behind the tub's access panel to feed the lav or other fixtures (like a bidet) and run a dedicated return. <!----><!---->
Operating costs can be quite high if the pump is oversized, the lines are not insulated, and the run times are longer than required. While standard tank-style water heaters have an 82% operating efficiency, they drop to an average of 63% if the stand-by time and temp losses are considered. Short-cycling, which can occur with a micro-load - such as a circ loop, can kill operating efficiency too.<!----><!---->
As you've noted, comfort and convenience often trump operating and/or installation costs. <!----><!---->
<!----> <!---->
I have been using a cross-over system in a 5 year old- 2 story- 4 bedroom- 2 ½ bath home for almost 3 years with very good results. The only negative I have encountered is that the guest bathroom doesn’t appear to be in the loop as far as eliminating wait times. I installed the pump and crossover under the master bath vanity which appears to be the farthest location from the water heater (both are on the second floor). Other than the obvious course of action to reinstall in the guest bath and test, is there a way of determining before hand if in fact I do have the unit installed at the farthest point? Thanks for any assistance you can provide.
I'll bite, too. Whatcha think of thermosiphoning? How do the numbers compare? I did it for the convenience rather than savings, and love it. It'll be interesting to see the numbers.
CH,
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Ahhhhh, my favorite method and what’s utilized in my home. No moving parts – except for the water. Drawback: since I’m moving hot water through my loop 24/7/365, I have higher costs due to Btu’s moving through the insulating jacket. How much is the real question and an answer that’s going to be a bit tougher to calculate than the pumped/timed system above.
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Gary Kline & I talked about this at some length. I’m going to remove the insulation from my loop, which starts as 1” copper and reduces to ¾” when it branches off to the master bathroom. At the beginning of the return, it’s reduced to ½”. Back at the SS indirect storage tank, there is a swing check with a small hole drilled through its check to regulate flow. Once the insulation is removed, I’m going to turn off the ball valve at the tank (on the return line) and let the loop go ambient. Once its at room temp, I’ll turn it back on and monitor the speed with which it travels to determine flow rate and monitor the outlet (155F storage) and return to determine how many Btu’s jumped ship. Then I’ll repeat the same experiment with the insulation in place to judge the savings and results.
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-->-->-->Gary-->--> noted they have seen temperature stratification in low flow rates where a hot “river” flows along the top of horizontal piping while cooler layers rest on the bottom. His tests have shown a need to adjust the faucet once “plug” flow pushes out the colder layers and the entire line is flowing with one temperature. We haven't experienced that problem. I’m anxious to see if my 1” horizontal run (about 60’ long) will show the same stratification. If the editors here will allow the link, you might enjoy this article from a few years back: http://www.contractormag.com/articles/column.cfm?columnid=62 Edited 10/17/2006 5:38 pm ET by PAH
Edited 10/17/2006 6:46 pm ET by PAH
Ive always wounderd about sizeing the pipe do you size the pipe in the normal way , large to small then use 1/2 inch to return to the heating sourse or do you maintaine one size throught out branching off and how far from the maine should you travel for a branch?
OK don't want to overstep my bounds or on someone's toes.
But I'll let ya know how we do it.
In our systems the size is determined by length of run & how many branches are coming back in a return pipe.
On a typical house those numbers are going to be on the smaller side, normally we would pipe as normal & pull a 1/2" line from the furthest fixture back to the source.
I wish my jobs could be that easy, generally I have sub zones due to multi story pressure limitations, usually incorporating a "maintenance heater" of some sort---- another subject another time <G>When asked why is there four engines on a 747------ "cause we couldn't fit six" a Boeing engineer
Spot on!
JJ,
Most size the main branch lines (for flow-through) in 3/4" with branch lines being 1/2". In order to avoid pressure fluctuations (not as big of an issue today if certified ASSE 1016 scald-guard faucets are utilized), the main trunk lines need to be a minimum of 1". Branch lines to all bathroom groups exit the trunk line in 3/4" and don't reduce to 1/2" until after serving the bathing module. The 1" must run to the curb line where it meets a short run of 3/4" from the water company. A long run of 3/4" will void the benefits of utilizing the larger 1" piping.
Home-run systems are an entirely different matter, although the line size and distance are important factors that shouldn't be ignored and often are.
The return line(s) can be much smaller and we have utilized 3/8" copper tubing in a number of retro-fit gravity systems without any adverse effect. The last one gave us a bit of start-up trouble until we realized it was air-bound - the soft copper had trapped air in an upside-down belly. Once forced out, the system worked like a champ.
Branch lines can extend for any length needed providing the length, line size and resistance to flow are accounted for when determining actual peak demand for flow at the fixture(s). Copper, PEX, PVC and CPVC each have their own flow characteristics and manufacturers publish charts to aid in system designs.
I was wondering if you could hook up an on-demand heater near where you are using the hot water (in my case, second floor bathroom) that would just work for the first few seconds to re-heat the water in the line from a regular heater (in the basement). Lots of up front cost--don't know if it would pay back. The on-demand would just be sort of a "booster" that would only fire for a short time until the regular heater kicked in. Once the regular heater was delivering hot water, the on-demand heater would trun off.
I guess the major problems are the cost of the on-demand unit, and finding a place to put it. It could be quite small though, since it would only be working a short time.
BTW, I knew someone who had hot water baseboard heat and they ran all their domestic hot water pipes alongside the pipes used for heating. In winter was never a wait for hot water! (Unfortunately, for whatever reason, they also ran their cold water lines in same way, so you had to wait for cold water in winter!)
HELP! I live in a house with a hot water recirculation system. System was installed correctly (using Laing pump SMT). House is three years old. House is a custom built home and is 5400 sq ft not including the garage. The system worked great for the first 26 months or so. For reason(s) I do not know the system now has taken on its own mode of operation. When I shower in the master bath I wait 20 seconds for hot water. I used to be able to take a 5 minute plus shower with no problem. Now the water will turn to ice after three minutes or so. This happens even if no one has run hot water anywhere for hours. At first, about 10 months ago, I thought it was the hot water heater. I called Rheem and they had a plumber come look. They said there was nothing wrong (it is a top of the line 80 gallon Rheem). I replaced the upper and lower heating element anyway. Plumber said it was probably the pump. I bought a new pump but there was nothing wrong with the old one as it worked fine when I plugged it into a 110V outlet.
I now shower by watering down for 60 seconds. Soap up and then rinse for another minute. Any longer and the water begins to get tepid.
I had another plumber tell me that the thermo valve in my master shower could cause this problem. Newport Brass sent me a new valve. I installed it according to instructions but the problem did not go away in the slightest. My wife tried showering this morning in another bathroom thinking that it would be different. This shower (like the master bath) is located fairly far from the water heater. Same thing happened. Left standing with shampooed hair in an ice cold shower.
We have another shower upstairs that is located virtually above the water heater. I can shower in there and the hot water seems to stay just fine. It never goes cold.
This tells me it is probably not the water heater. I do not know about the pump. When I walk up to it you can feel and hear it running. However, there are times when it takes 20 to 30 seconds for hot water to arrive at a faucet. The hardest part to all of this is that it worked for two years without a glitch. Any suggestions?
Fixer Daddy
Well there are a lot of details that aren't know. Does it have a separate return line or use the cold water return? If separate where is the return connected to thw WH?Where is the pump in the system? What kind of controlls? Time clock? Thermobypass valve? Thermostat? And where are they located?But when you have the problems fell the pipes and see what is warm and what is hot and what is cold?And if you can't access the pipes near the shower then run water in the vanity and fell the pipes under it.
Sounds like (tugging on my ear)........
Reverse flow of cold up the recirc loop. Next time your wife (or you) use the shower, have the other person stand-by the recirc loop and feel for a cold reverse flow.
I'd have fingered the water heater's dip tube except for your description of one shower not being affected. Sounds like that one is not along the route that'a served by the recirc loop.
Dear Experts:
I read with great interest the article in FH183, but I am left with a question about the safety of using crossover valves in retrofit installations. Several years ago, the California Health Department spent the money to send a letter to every homeowner in the state to recommend they avoid using hot water for cooking because of higher lead contamination in hot water pipes, since lead in joints leaches more into hot water than in cold.
Well, if you start pumping hot water into cold water pipes, wouldn't you be drawing lead from joints which previously were only exposed to cold water?
Of course, one could argue that you could test the water before installing the crossover valve. But that might not be a conclusive test. If you test the cold water, you'll get a reading of the lead content when the pipes are exposed to cold water. If you test the hot water, you'll get a reading of the lead in pipes that have been exposed to hot water for decades. What you want to know is the lead content coming from pipes that have never been exposed to hot water and are all of a sudden exposed to higher temperatures. But that is information you can't get until you have installed the crossover valve and possibly also the protective layer of oxydation or minerals has worn out.
How ridiculously paranoid is that?
Thanks for giving me your opinion on this.
Yann
Well, it is Kalifornia! The Governator just signed a new lead-reduction bill for faucets.
It's been a long time since lead-based solders were banned in the US, so I wouldn't personally lose any sleep over this issue - but - I'd be perfectly happy to provide a quote (if I lived in the area) to replace the lines!
In general, it's not advisable to ingest hot water & utilizing hot water to jump-start cooking times doesn't save any energy.
Lead is readily adsorbed through the skin in a bathing environment, so if you've got elevated levels present and have someone with elevated blood-levels, bathing in lead-contaminated water will make their condition worse.
Here's two for the road:
http://www.contractormag.com/articles/column.cfm?columnid=97
http://www.contractormag.com/articles/column.cfm?columnid=103
Here's the current month's article (I forgot to post the link before - sorry bout that) regarding mechanical recirc I wrote for CM. http://www.contractormag.com/articles/column.cfm?columnid=584
Hi Brian,
Just read "hotwater now"
I understand that most of the installation problems will be in backfitting this idea in existing houses.
I like to focus-in on comfort and not economics for a moment.
The article talks about the installation of Crossover Valves. Easy to do in kitchen cabinets and bathroom vanities. However these places can be readily outfitted with an auxilliary waterheater.
The article never mentions the shower and how to solve the problem there.
Of course there seems to be no way presently to backfit a Crossover Valve in the shower. Industry surprisingly has not provided a solution to the "Hot Water Now" in tiled showers in existing homes.
My idea would be for the industry to design an attractive Crossover Valve /interface inserted between the hot /cold water escutcheon and the shower manifold.
Installation is as follows:
Remove existing hot/cold water control plate from the tiled shower wall. Install Crossover Valve backfit kit for the model valve manifold installed in the wall. Reinstall hot/cold water control by mounting it on top of newly installed Crossover Valve assembly.
One can expect the finished product to be elevated from the shower wall equal to the Crossover Valve interface.
Please comment on my letter
Kind Regards.
John
This properly designed pancake -shaped manifold with its required gaskets
There is no need for it in most cases.You get hot water to the vanity.The shower is connected on the same run and will only have a second or two more for water to get to the shower.
I have an older home with a few long hot-water runs. I'm interested in a recirculating system and have easy basement access, so a return line should be simple.
The "Hot Water Now" was pretty clear except for one thing. Where does the return line rejoin the water heater? The diagram shows the pump mounted to the side of the heater. The water heaters I've seen have a cold water supply and a hot water out connection. What is the side connection shown in the article? Do you actually reconnect to the cold water supply? Or, do you connect to the pressure relief fitting with a tee?
Thanks.
BigJAF
Dear BigJAF: The drawing in the article was of the Grundfos Comfort Flow, one of three types of recirculation system used in retrofit applications. In this system, the pump is located on the hot water outlet of the water heater and you install the aquastatically controlled valves under a sink far from the water heater. The valve allows the water from the hot line to cross over into the cold water line which acts as the return to the water heater. Please note that the pump is controlled by a timer which you set to the hours when you anticipate hot water use. The pump runs continuously during these hours, waiting for the valve under the sink to open. It then moves the water relatively slowly through the valve ( very small opening) until the water reaches the shut off temperature (roughly 105F). This means that there will be rather warm water (105 down to ???) on the cold water side.
I would suggest that you look into the demand controlled circulation systems. They can be installed in both retrofit (cold water return line) and "new construction" (dedicated return line like you are suggesting) applications. They only run when you "tell" them to by pressing a wired or wireless button or walk past a motion sensor to activate the pump. The pump moves the water very relatively quickly and turns off when it sees a rise in temperature of 5-10 F. Instead of setting the anticipated hours of operation (and having to wait during periods when you didn't plan for hot water), you activate the pump shortly before you want hot water. Instead of running for hours every day, demand controlled circulators only run for minutes. They are the only type of circulation system that I have seen that can provide the convenience we desire, save water and save energy (by using less energy than is associated with running water down the drain.
If you are able to install a dedicated reurn line without much trouble, that is what I would recommend. In that case, the pump can be located on the return line near the water heater or right after the last fixture on the loop. A lot of installations seem to have the return line connected into a tee that uses the drain line, but it is also possible to tee into the cold water feed to the water heater. The demand controlled pumps have a built in check valve.
You might also want to look into http://www.waterheaterrescue.com which is a website that shows you how to extend the life of a typical tank type water heater. The book they recommend is excellent!
Hope this helps. All the best. Gary
Dear All: I promised to find a way to get everyone access to a series of articles that I think will be helpful to those on this discussion thread.
Here they are. Enjoy!
All the best. Gary
Here are the 3rd and 4th articles and the presentation made at ISH (very similar to the one given in San Jose for PG&E.
Hello: What are your thoughts on the RedyTemp hot water recirculation approach?. It seems to simple. For new constuction it appears it would save on plumbing labor, etc. It looks simple to install. WHAT am I missing .
Thanks
Cloudbuster
At $375 it looks like a reasonable solution, similar to the Laing system or the Taco or Grundfos brand. I still thing the best of them all is the D'mand. And that is the only one that picks up LEED-H points and hopefully will soon have points from the NAHB-ICC National Green Building Guidelines.------------------
"You cannot work hard enough to make up for a sloppy estimate."
For the "energy savings" I agree the D'mand system is the only one recognized by energy org's to save. But in real life, I think it's asking a lot for people to push a button . . .wait 20 - 30 seconds. . .one, one-thousand one. . .one, one-thousand two. .. one, one-thousand three. . .seventeen more to go... Then, turn on the hot water faucet only to receive water 5 deg's higher then room temp. So, your still waiting for the hot water needed 105-110 while water goes down the drain.
Anybody know what temperature mark was used in the qualification of the D'mand system for the energy savings test performed on it to achieve it's energy rating? What were the details of the test? Try taking a show in water that's only 5 degree's higher then room temp.
Life is too short...365 days in a year times the number of uses per day...times how many seconds? That's a lot of waitin. Where's the convenience.
>>Try taking a show in water that's only 5 degree's higher then room temp.
Maybe you mean body temperature? Room temp. wpould be 72 degees F and 5 degrees highe would only be 77. that would be a cool shower.
Dave
If I recall correctly, the D'mand system stops pumping once it reaches 5 degree's above ambient room temperature. Correct me if I'm wrong.
Ah, found it... http://www.thesolar.biz/Metlund_Hot_Water_System.htm
Somebody say BRrrr.
I'm hav'n a problem understanding the below statement from their website. I must be work'n to hard...anyone care to clarify for me.
Will it work with water softeners?
Yes. When there is a demand for hot water, the cold water line will be purged because we always mix hot with cold to reach a comfortable temperature.
We've been using the Grundfos and Laing systems for a long time and they keep the water hot all the time and the homeowners love them but it bothers me that they burn energy when your at work or asleep. The Maitland D'mand system uses a very high speed pump and a 3/4" return line and can be activated by a button in the MBR and a motion sensor in the guest bath. The assumption is that the return line will double as the cold water supply so you don't want to fill it with warm water. The pump brings hot water from the water heater to the bath when the owners push the button or the guests open the door. This way the owners can use the WC in the middle of the night with out wasting hot water. Once enough hot water has advanced from the water heater to raise the temp to 5 degrees above room temp there is a full line of water heater temp water ready to go to your hot water tap. It's actually a very sweet system and has the advantage of not using any energy while you are at work or away from the house. Still, most of my clients don't want to push a button so I still install Laing and Grundfos in most of my houses. We also spray foam the attics, walls, and both hot and cold water pipes so our loss in somewhat minimized. and we install solar hot water on most of our homes so I'm sort of splitting hairs about the stand by losses, nerd that I am. ------------------
"You cannot work hard enough to make up for a sloppy estimate."
I understand that your customers might not want to push a button for hot water. I was in the same boat until I recently installed such a system and find it to be quite acceptable. The problem with the Laing and other systems like it is that the energy loss from having hot water in the pipes is substantial even if it is on a timer. Some data I have seen indicates that a recirc loop runing 16 hours a day can cost more to heat the water for the loop than for heating the water that is actually used. Such a loop can apparently double to operating cost of a hot water system.
Bill
that would be a cool shower
LoL!
Now, for the last month or so, "room temperature" at my house has been 78-82º; but, an 84-86º shower is still right chilly, being below body temperature.Occupational hazard of my occupation not being around (sorry Bubba)
Can you or any of the other experts advise me on why PEX is not recommended for the return line of a thermo-siphon hot water loop by the manufacturers? I am preparing to replace the copper 3/4" supply line and the 1/2 " return line in my 35 year old house due to "numerous" pin hole corrosion leaks. I thought I was settled on the advantages of PEX until I kept running into this no use recommendation.
thanks in advance for any assistance offered. Willie
Ive been installing PEX on the return lines of my recirc loops for years with no problems. Qest and some other plastic pipes have had problems over the years with plasticizers leaching out of the pipe causing it to get brittle when used with recirculating and radiant piping systems. There may be a chlorine component to this story, I seem to remember a lot of problems in Las Vegas having to do with the water chemistry there being aggravated by constant hot water in recirc loops. With closed radiant systems the chemical might react with the pipe but since you aren't adding more chemical every time someone takes a shower it's less of an issue. Since PEX has had great success with radiant I can't think of any reason why it shouldn't work on the return side of a recirculating hot system. ------------------
"You cannot work hard enough to make up for a sloppy estimate."
Thanks for the responseon the use of Pex in a hot water recirc. system. Alternate research I did on internet sites brought up manufacture's testing that suggested that if the clorline level was about twice as high as a typical community water system then over the course of 40 or more years Pex could be expected to develope pin-hole leaks. The same thing that started happening to my copper piping after 25 years. I think I'm going PEX for the next 30-40 years. If something goes wrong before 2037 I'll post an update on my 88th birthday. Thanks again ; Gtownwillie