Home Run vs Trunk/Branch Systems
CarletonPope
| Posted in Energy, Heating & Insulation on
Plumbing isn’t really covered here, but I’m wondering about what you folks thinks about traditional trunk/branch plumbing systems, versus home run manifold systems?
Cost is a concern for me, but I like the home run system because you have fewer (if any) mechanical joints in the floors and walls. PEX is cheap, so I’m not too concerned about slightly more tubing cost, but manifolds for radiant heat seem quite costly. Perhaps they’re the same thing as manifolds for home run plumbing systems?
Also, I’m wondering if home run systems completely isolate each fixture from all the other fixtures in the house. In other words, if I’m having a shower, and the wife flushes the toilet, will I notice a change in water temperature/pressure?
-Carleton
Replies
My own home is using a home run system. I would never build one for myself any other way.
I've been looking at higher end home builders lately and I'm seeing more and more home run jobs.
You should also look into what they call a remote manifold system. It's not your traditional trunk and branch, and not a home run system either. FHB had a decent article about all this a few months ago. I think they concluded remote manifold was probably the best way to go as far as cost and performance.
I didn't read the article on the remote manifold system.
I'm thinking you run 3/4" to a manifold under the sink. Or if you have access like a crawl space under the bathroom. But you could fit under a vanity. Especially a double.
Then run 1/2" to the fixtures in the bathroom.
That way you only have two 3/4" lines going to the bathroom and no connectors in the walls.
Once you get the hot water to the bathroom you have hot water at all the fixtures.
Well, minus the distance for under the sink to them. Not far.
Yeah pretty much... I don't think the manifold has to be right under the sink... just in the vicinity of a group of fixtures. Manifolds without valves can be enclosed... but manifolds with valves need to be accessible. Here is a link to download a PEX water supply design guide. Pages 27-30 show each of the three methods of installation.
http://www.toolbase.org/Design-Construction-Guides/Plumbing/pex-design-guide
Manifolds are not very expensive. The Sioux Chief brand is wrought copper, and they make a good variety of branch options.
A manifold system helps reduce fluctuations in pressure, but will not entirely eliminate them. For best temperature consistency in the shower, install a pressure-balancing shower valve, such as the Moentrol. Such shower valves keep the same proportionate mix of hot and cold, so what fluctuates is the volume of water, not the temperature.
The biggest advantage of the home run system is being able to run small diameter lines. These waste less water, both hot and cold.
Both can work well, but I prefer HR. We've got one and love it. There is absolutely no effect on any one fixture by another.
Scott.
There is absolutely no effect on any one fixture by another.
You could probably say the same thing about a properly sized branch system.
MikeInsert initially amusing but ultimately annoying catch phrase here.
One thing I wouldn't like about a home run system. You go into the bathroom on the other side of the house from the water heater and turn on the sink and wait for hot water.
Then you turn on the water for your shower and wait for the hot water. You have to drain all the cold water out of both lines to get how water. Doesn't make much sense to me.
"One thing I wouldn't like about a home run system. You go into the bathroom on the other side of the house from the water heater and turn on the sink and wait for hot water.Then you turn on the water for your shower and wait for the hot water. You have to drain all the cold water out of both lines to get how water. Doesn't make much sense to me."Yes, if you had a branch system and you turned on the sink first that would get the hot water going through the main line, then when you turn on the shower the hot water would already be there. But, if you hadn't turned on the sink first and went to the shower only, I think a home run system would be advantageous in that the hot water would get there quicker because only the showers 1/2" home run line has to be cleared of its cold water (as opposed to a 3/4" main line)I don't have a home run system but I had always understood that one of the advantages of it is that hot water actually gets to the fixture quicker because the volume of a 1/2" line is only about half of a 3/4' line.
>>>I don't have a home run system but I had always understood that one of the advantages of it is that hot water actually gets to the fixture quicker because the volume of a 1/2" line is only about half of a 3/4' line.
That has been my experience. Even the farthest runs from the manifold, which is placed dead-center in the house, take only a few seconds to heat up. Perhaps the other poster was comparing to a recirc system, which isn't really comparing apples to apples.
Scott.
Would you consider putting a manifold in the center of your house a remote manifold system?
Because my water heater is in a utility room on one side of the house. I can't move that room really.
But I could run hot water to a central location where a manifold would distribute it.
You are right about "Perhaps the other poster was comparing to a recirc system".
I'm going to install a reticulating system in the future. I think it is the best in my opinion.
It is pretty far down the road but I have bought the insulation for the pipes.
I should be getting a new water heater next week if the supply house gets it.
They forgot to put it on the truck last week.
I prefer a manifold system. Take for instance the bathroom. If you have a home run system, you must bring hot water to sink, then again if you want to take a shower. With a manifold, the hot water is brot to the sink and then is ready for use in shower.You get out of life what you put into it......minus taxes.
Marv
>>>Would you consider putting a manifold in the center of your house a remote manifold system?
I'd be concerned about all that wasted energy leaking out of the pipes between the manifold and the WH. First thing in the morning you'd have to wait until the entire system recharged with hot water. Can you move just the WH (rather than the whole room)?
Scott.
No! I'm just mess'n with ya. But seriously, I can't move the water heater. Well, at least not very easily.
I've solved my hot water across the house issue. I've made up my mind to install a re-circulation system.
By the way. Why is it re-circulation? Why not just circulation?
Back to manifold systems. I was asking the question rhetorically. I didn't see the article on remote manifold systems and would like to know if putting a manifold in the center of your house would be considered a remote system.
What is considered a remote manifold system? Does it have to be in the bathroom or adjacent to it to be considered one? Inquiring minds want to know!
I could just sign up for the online service and read the article. But noooo!
To take best advantage of the HR system, run the lines as small as practical, which means running 3/8" for most fixtures. This might sound small, but consider that, at 50# water pressure, a 3/8" PEX line will deliver 5 gal/min with a 50-foot run of pipe. This means that the 3/8 line will carry far more water than faucets can deliver in these days of water-conserving fixtures. Shower valves, for example, can deliver only 2-1/2 gal/min, and that's the combined flow of hot and cold.
Delivery times: a 20 foot run of 3/4 pipe at 2-1/2 gal/min flow will need about 12 seconds for the hot water to flush out the cooled water. A 3/8 line will need only 3 seconds. And you will have wasted only one-fourth of the heated water. The 3/8 line will waste only about 12 oz. of water.
A re-circulating system will use more energy because of the heat loss whenever the system runs--your hot water pipes become a radiant heater, in effect. You can minimize this by installing a timer on the re-circ pump set to operate at times when you know the hot water will be needed, say, 6-9 in the morning, and 5-10 at night.
I always hear about pressure drop with smaller lines. Usually it's comparing 1/2 to 3/4, so on a well pump would you
still recommend 3/8 ?
I ran 1/4" tubing to my bathroom sink to reduce the water wasted while waiting for hot water to arrive at the sink.There is a noticeable pressure drop and the volume is low but I don't need pressure or volume at a bathroom sink.I would do a test run with 3/8 pex and see if it is acceptable volume and pressure drop for your shower. I would definitely look into downsizing my hot water lines to 3/8" to reduce waiting for hot water.In my first home I ran 3/4" hot water lines and kicked myself for it every time I ran hot water and had to wait an eternity for it to arrive.Karl
There are limits to a home run system. Proponents of it tend to over look them.
What if had a tub at the end of the system? Would you like to fill it quickly?
What if your bathroom is considerably more than 20' away? I do think there are many people with a bathroom much further away than 20'.
If you insulated the circulation loop well would that reduce the energy loss?
What if you used PV for the small 12V pump? A timer helps also. But if it is insulated well and the pump is powered by PV That might be acceptable.
I do believe that water conserving fixtures are the way to go. But there are some situations where more volume is desired.
I have a house that has a good size crawl space under the length of the house.
If I install a loop using apex, insulate it well, and use pv for the pump it should last a long time. And I will have hot water almost instantly anywhere in the house and there will no pressure drop.
I will go through many water heaters before the loop even begins to show age.
I would also like to install domestic hot water solar as another loop that exchanges with this one. I haven't quite figured that out yet. I built a roof that is perfect for collectors. And I live in No Colorado which has a lot of sun.
This is what i want to do. I don't think it is for everyone. I never said that. I will say that the home run/pex system isn't the end all that many people say it is.
In my opinion home run systems are overrated. I think you should run a main trunk line to somewhere near your bathroom to a manifold... and run 3/8"s or so to your fixtures from the manifold. The manifold can be a flow through manifold. Have a re-circ. pump at that point. I think this is pretty much what you are planning on doing...
It's what I want to do. I don't think it will be that hard and the results should be pretty good.
I was thinking of going down into the crawl space and fiuring out what size the loop would be and where the Ts would be.
Then build it outside on the lawn laid out like it would be in the crawl space.
I'm not sure if i would insulate it on the lawn. Maybe if I had a helper to handle it more carefully.
I plan on hanging it just below the floor joists. A 3/4" pex loop the length of my crawl space with Ts in it for the lines up to the fixtures.
Thanks for all the great responses. I'm much more edjumacated on this topic now. Like everything in life, many different opinions on how to do things. ;)
-Carleton
however the feed for the manifold only has to be the equivalent of the largest fixture on the manifold, if it is acceptable to say that the sink and shower in the same bathroom shouldn't be used together.if you have to run multiple fixtures off of the manifold at once, you can't do that, but it is entirely feasible to run a 3/8" feed to a manifold of 3/8" fixtures and then you have truly the best of all worlds from an efficiency of material and energy standpoint... and you can even still do timed recirc (and recirc should always, always, always be timed) from the manifold.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Certain fixtures, such as a large tub, will need 1/2" home run lines, but most fixtures don't. Toilets, sinks, showers, clothes washers, and standard-size tubs all perform very well on 3/8" lines.
Of course, there will be cases where fixtures will be more than 20' away from the manifold, and those are actually times when the small, HR lines perform even better than a trunk and branch system. (Up to certain limits--if you have fixtures more than 50' from the manifold, there is enough friction loss to warrant the use of a remote manifold, which is simply a secondary, or auxiliary, manifold located closer to the group of fixtures that is fed by a 3/4" line.)
Insulating the hot lines of a re-circ system is a good idea in almost every case. The advantage of the HR system, however, is that with small lines you really don't need to insulate in most cases. Keep in mind that most bathrooms or kitchens go thru "punctuated" periods of use: you use the bathrooms in the morning or evening, and they sit idle thru the day. Same for kitchen. Once you heat up the line to the master bath sink, for example, the water in that line will be hot instantly for the next user during the next 10-15 minutes. So, once the period of intense use is over, it is a waste to keep a re-circ system going. There will be heat loss even with insulated lines.
In general, the hot manifold should be located as close to the water heater as possible because the volume of hot water in the 3/4 line from the water heater outlet to and thru the manifold will be as great at some of the shorter 3/8 fixture lines.
You sound like you are just as convinced that a home run system is the best as I am convinced that a circualtion system is best for my home.
You must plumb your house like I say! Or...or...or. Well, on second thought, since I'm not paying for it, maybe you oughta do what you want.
I can tell you, however, that in my job as a plumbing inspector, I have seen literally thousands of homes with HR systems in PEX, and hundreds with re-circ systems. Unless your home is huge (as in 4000 sq.ft. or more), I believe that the extra expense and operating cost of a re-circ system is not worth it.
If your home is really big, then you might do well to install two water heaters, one at each end where plumbing is concentrated.
No problem ;^) I can be pretty stubborn when it comes to some things.
And I like, no, I love building things I've thought through.
Edited 3/30/2009 11:18 pm ET by popawheelie
Would you have any data on initial and operational expenses of comparable HR or recirc systems that you could share on this post?
The info would be greatly appreciated.
Bruce
Installation of the HR system will be cheaper (I can't give you an exact $ figure), mainly due to the cost of extra components required by the recirc system. Pump, isolation valves, check valve, and possibly an expansion tank that may not otherwise be needed on a system without a check valve. (A check valve creates a "closed system", meaning that the volume of expanded water can't push out into the water main, and there would be danger of overpressurization of the hot water tank if there were no expansion tank to accept the extra volume.)
A trunk-and-branch system made of PEX would be cheaper than a PEX HR system, but not much cheaper. The extra cost of the HR system in this case would be the cost of greater total length of pipe.
For the average size house, say, 1200-1800 sq. ft. the recirc system will use more energy with the average family's punctuated use. (6-9 in the morning, 5-10 at night.) How much more? Hard to say, exactly, but my guess would be about $150/yr. between running the pump and radiation loss from the recirc system as it operates over an extended period of time.
If you're thinking of using copper lines in a recirc system, be extra careful to ensure that no part of the recirc system exceeds a velocity of 5 ft/sec. This is because hot water at a high velocity will erode the copper due to cavitation. The explanation is lengthy, but the fix is simple: just make sure the pump's output is small and that all parts of the recirculated system are large enough to keep velocity below 5 ft/sec.
As a general comment in favor the the small-diameter HR system, Washington State University did a study about 10 yrs ago that found that a family of 4 would save about 2500 gallons a year, most of which would be hot water, since the greatest waste of water is what goes down the drain as people wait for cooled water in the lines to be flushed out of large lines in a trunk-and-branch system.
"Certain fixtures, such as a large tub, will need 1/2" home run lines, but most fixtures don't. Toilets, sinks, showers, clothes washers, and standard-size tubs all perform very well on 3/8" lines."
Interesting. I assumed a shower head would be one fixture requiring a 1/2" line. Are they all restricted to 2.5 g/m?
On a related note, I want to set up a two shower head unit in my bathroom (two shower heads, one control valve) Would one 1/2" line handle this? I had figured on running a 3/4" line.
Thanks
Shower heads all use 2-1/2 gal/min unless you get into the fancy types that recirculate the water with a pump system. The rest are federally regulated to be low-flow like toilets, and, like toilets, manufacturers have come a long way in designing them for excellent performance. The early models, like 10 yrs ago, did not perform as well.
A 1/2" line will easily handle two shower heads if you have 40 psi or more water pressure.
>>>What is considered a remote manifold system?Good question; this thread is the first I'd heard of them. Mine's just the conventional beside-the-water-heater type.Good luck with the project,Scott.
The entire system wouldn't have to recharge. the first person to use hot water would have to wait for the 3/4" line to fill up from the waterheater to the manifold.
From there on out it would be the 1/2" or 3/8" lines. Three seconds. So the first person has to wait a bit.
And you could insulate the line between the water heater and the manifold so it would stay hot for a while. Until the sleepy heads woke up.
Edited 3/27/2009 8:42 pm ET by popawheelie
You are right that the 1/2" line gets it there with less water wasted.
I don't think there is that much difference between 3/4" + 1/2" time wise.
I would not want to have to wait for both the shower and the sink to have hot water arrive. That would not be acceptable to me.
People are jumping on the pex home run system thinking it solves all the limits that the old trunk system had.
That's just not the case. There are limiting issues with a pex home run system also.
I think a lot of the attraction is that it is new, easy, and copper is up $.
Same thing with shark bite fittings.
If people have had problems with a trunk system it is probably because it was designed badly. I'm not saying a traditional trunk system is the best either.
"I don't have a home run system but I had always understood that one of the advantages of it is that hot water actually gets to the fixture quicker because the volume of a 1/2" line is only about half of a 3/4' line."Not quite. Volume of 3/4" pipe is twice that of 1/2", but friction resistance in 1/2" pipe reduces pressure 6 times as much as in 3/4", so you lose some of that advantage in a shower where you need pressure to push enough volume out of the nozzle.http://ths.gardenweb.com/forums/load/bath/msg081339241057.htmlBruceT
You don't lose any appreciable advantage.You reduce volume, and increase velocity in smaller pipe compared to larger pipe.that reduces total POTENTIAL flow rate, it's true, but in most cases, the total flow rate was already restricted by other items in the like, like the faucet. Your showerhead, for example, wasn't going to push 5 GPM just because you had a 3/4" line on it, so it doing 2.5 GPM with a half inch line instead of a 3/4" line: as long as you have the PSI to make this happen for your run length: is really about twice as fast.In other words, when flow rate stays pretty much the same because the previous line size was OVERSIZED, there is great benefit in downsizing the lines.If you have a 'dump fixture' that can pretty much take whatever you can give it, then you're right that the advantage is not "twice as good"... but it's still going to be very noticeably better.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com