Open radiant floor systems
I have spent some time researching radiant floor systems, and would like some input about the open system that is promoted by Radiantec and other companies that cater to the DIY. Every professional HVAC that I read the opinions of say they will never use such a system because the potable water will stagnate all summer, making it unsafe. While I may respect their professional status, they never address the design which insures that the potable water always flows through the floor tubing prior to arriving at the faucet, so the system is designed to prevent stagnation. Does anyone have an opinion on the subject? Is there really any validity to the stagnation argument, or is it just “tradition”? If you are agains’t such a system, please explain why.
Thanks
Replies
Doc, I'm a general contractor and not an HVAC contractor, definitely no specialist in radiant flooring. With the disclaimer out, I'll throw you my thoughts on this. If you've been doing your homework this thought may have already crossed your mind or may have been addressed by the company you mentioned.
As a builder, we use only closed radiant heat systems when we do use them. We use Gypcrete to cover the tube to give the system the thermal mass that makes it so effective and we install a boiler system to heat the water to about 180f before sending it through the tubing. My concern with an open system is as follows. First, if you use a typical hot water heater to heat the water to the desired temperature, any taps which run off the heater without the radiant floor as an intermediary would produce scalding hot water. And second, I don't know of a standard hot water heater which would get the water hot enough to really make the system efficient on a large scale basis. Third, Even once the temperature of the water is heated to a temperature hot enough to heat the floor, my concern would again fall to the tap temperture, which in my neck of New Jersey must fall within a 5 degree range for our CO. I think it would be tough to hit that range when loosing heat to the floor. Lastly, I promise, is with an open system, it seems to me you will have a heating system that is always on.
Like I said, you've probably addressed these questions already, but if not it's some food for thought.
Good Luck,
TM Rapp
I am a homeowner not a prof.esional.
We have an open system that I designed and installed with the help of my husband. This is a small house, 1200 sq ft. 2" slab on a plywood subfloor system. I have the plumbing installed so that I can run cold water through the floor system to the hot water in the summer. I change this in the winter so the water runs to the hot water first. This is our second winter and the system is working fine. We have only two zones and I do periodically in the summer manually run water through both zones as to make sure there is no stagnant water.
This works very well for us. It is a small system.
Jill
Thanks for your response. Most of the systems that I have read about (both open and closed systems) require a much lower temp than the 180 degrees that you quote. The systems that use boilers at 180 degrees use a mixing valve to lower the temperature of the water to 120-140 degrees, depending on the needs of the system. That is one of the reasons that the open system is said to be more effiicient, only needing to heat the water to the required temp.
Both doc and Mongo are correct. I apologize for the misinformation regarding the water temp my radiant contractor runs through the system. We rely on closed systems because of the square footage of flooring we cover, anywhere from 5,000 to 10,000 sf, and the number of zones used, as many as 10. If anyone has any information a open system would function more efficiently on this scale please let me know, I am always open to change...
TM Rapp
TM,
I'm with you in your preference for closed vs open systems.
A big question is what is heating the water in the first place. If an oil-fired boiler...which is prevalent here in New England, then it's 160-ish tempered to 110-120.
If gas is available, then a water heater dedicated to the RFH can supply water at 120 right out of the heater. It's a very simple setup.
Regardless of choice, I'd still prefer a closed system. You can still run a single water heater with a heat exchanger. The water heater heats the DHW, the HX heats the RFH.
I'm not a fan of anti-freeze in RFH systems...unless they're unoccupied second homes...but obviously, if anti-freeze was warranted, it'd require a closed system.
I've designed both types of systems. Each has its place. The stagnation issue is probably an extremely rarely occurring problem but if it concerns you put a timer on your pump or in parallel with your thermostat that circulates the water for 3 or 4 minutes once every two weeks or so. I have an open system that serves my garage floor. I built the garage on the house 5 years ago. I needed a new water heater anyway so I installed a 40000 BTU input 50 gallon natural gas unit instead of the 30000 BTU 40 gallon unit I would have otherwise installed. Since the coldest day of the year only occurs once or twice a year I never run out of hot water in the shower on the other 363 days. I have the water heater thermostat set at 130 degrees (yes a little on the warm side) and a mixing valve that drops the water going to the garage floor to 70 degrees. I circulate the water in the garage non stop all season. Makes for a very simple, inexpensive system.
The closed systems I have done are in dairy barns. The last one was a 7000 sq foot system with some extreme air change factors. When serious BTU is necessary a closed system usually makes more sense. In fact usually if a lot of heat is needed to keep a building comfortable it works very well to do indirect domestic water heating with the domestic system wired for priority.
Rule of thumb: If the required radiant heat load is less than 10000 BTU an open system off the water heater usually makes sense. If the required radiant heat load is over 50000 BTU a dedicated heating appliance and a closed system usually makes the most sense. Between 10000 and 50000 other factors will usually throw the decision one way or the other.
If you are governed by a code, others who consider themselves smarter than you will make the decision for you.
Kevin
Someone could just slap me in the head and yell "duh", but somewhere in my travels I remember an article discussing the best way to heat a shop. The article (show or discussion, I can't remember) demonstrated the very obvious setbacks with most units because of the amount of airborne sawdust and the possiblity of flashover or afixiation from propane or kerosene fired units at worst and a completely clogged forced air system at best. Radiant in a shop seems in my mind to have no drawbacks providing the boiler (or hot water heater) used is in a seperate room. Even baseboard would become clogged. And an existing shop could be retrofitted using a undermount or radiant subflooring installation.
Can anyone think of a drawback to this?
t
Kevin and, of course, Mongo gave good info. I have had both systems in my own homes and am not concerned about stagnent water issues (have worked professionally as a plumber, 14 years as an environmental engineeer, my PE is in Civil, my wife is an MD, internal medicine). My reasons are as follows:
Since I don't close valves to isolate loops when it gets above 40F ambient (my non-heating season), there is always some circulation in the loops. Since it is potable city water, it is chlorinated when it goes into the loops. The loops are food-grade materials.
As others said, code intrepretation may well force your choice. Otherwise, in a tight house, either will work. Do your own work, and you can pick the one that makes sense to you. If someone else is installing it, go with what they are familiar with. You don't want to be the first example of anyone's work on new-to-them configuration.
Personally, I prefer open systems when allowed because of the reduced parts count, lower electrical consumption, and lower component costs. That said, mw snow-melt sidewalk is closed-loop because it, obviously, is filled with (non-toxic) anti-freeze.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Here I am...in suburban CT...on my own well. There you are...up in AK...on city water.
It just doesn't seem right!<g>
I installed radiant loops in my new 40x60 shop floor slab, and am planning on running radiant heat with a small boiler in a seperate sealed off boiler room. I have a hanging forced air propane unit I will use just for quick heat as neaded. What I really would like is to come up with a good design to burn scrap wood, tied to the boiler system, but that's for later.
Bish.
In the early 80's, my parents bought a house in West-Central Jersey where the builder installed heat pumps of all things. Needless to say, they quickly started searching for an alternative. They found it in a coal fired boiler which was mated to their forced air system and served the purpose rather cheaply. I know wood fired boiler units exist, but don't know where you could find them. Think wood fired hot tubs one can often see advertised here and there.
Regarding the "small boiler" you really should not need more than a domestic hot water heater running on propane/oil. The radiant heat folks suggest a hot water heater should be more than adequate for 400' of 5/8" OD PEX.
WndyWood,
You're not heating the pipe. The size of the heat source and the footage of pipe are only very loosely related. The size of the heat source has to match (or exceed) the heat the heated area will loose. A rule of thumb that sizes heat sources by the footage of pipe is no better than a driver who airs up car tires by time. Big tire fill for long time, small tire fill short time. If you have no idea how big the air compressor is or what pressure is available or how much air was in the tire to start with how are you going to know when to stop. To size a heat source, you need to know how cold it gets outdoors, what the heat loss is for the structure at that outdoor temperature, and if there are any other sources (or losses) of heat in the structure.
Often with radiant heating there are multiple acceptable solutions but you always have to do a little math to know what they are.
Kevin
I'm not sure if you're Kevin or Melinda but my statement about a hot water heater being adequate for some radiant floor systems is indeed a generalization and not based upon engineered knowledge. I will say however that my 325 square ft shop built on a slab with 5/8" OD PEX tubing at about 14" O/C provides me with a working temperature of 62 degrees MINIMUM using a 30 gallon Bock oil fired hot water heater. At outside temperatures of -5 the unit fires about 12 minutes every hour cycling twice an hour for 6 minutes per cycle. We get to -20 at times so I'll have to let you know how it does then. I've pretty much designed the system to run continuously with mixing valve electronic control producing a 12 degree temperature differential. my outgoing temperature is set at 90 F. I figure that the 30 gal heater is overkill but it is a fairly efficient critter so I'm probably not sacrificing much in the way of fuel consumption efficiencies.
Indeed you would have to do a lot of math to configure a system according to engineered standards taking into consideration the insulation under the slab, the walls, ceiling height frequency of door openings, amount of Southern exposure, desired floor and ambient temperature, lag time, overheating factors, heater efficiency, pressure losses, circulator flow rates and I'm sure a dozen other components.
When I asked two of my hydronic engineer buddies for advice they said to run 5/8 OD PEX at 16" O/C or 7/8" PEX 20" O/C, configure the differential at 15 degrees F with a 30 gallon hot water heater, Grundfoss circulater and one continuous loop. They figured that this setup could heat the place to 85 F if I wanted to on the coldest day of the year. They were right! Sometimes common sense is worth a lot of calculation.
For those who would enjoy a primer on radiant installations this is a website for an outfit in Vermont that has been putting systems in for quite a while. They were a big help. http://www.radiantcompany.com/
WindyWood
TM,
Don't you temper the water off the boiler before sending it through the slab?
We just went through the same decision set for a house we're buidling for ourselves. The clincher was a comment from the heating design guy at our local supply house. He was concerned about condensation in the summer caused by 40-50 degree water flowing through the floor with our typical high humidity in the summer. The thought of condensation forming on a wood floor was enough for us to decide to go with a closed system.
Go to JLC website.
http://www.jlconline.com
Then under Research Tab Heating section. There is an article on doing this. And he discusses the pros and cons. One big thing is the local interpretation of the codes. So you want to check that out.
Some of the articles are $5 each, but I think that this one is free.
Be aware that Radiantec selld inferior quality tubing as well as other parts. If you want quality stay away from them. They have faulty info on their website bordering on fraudulant. Why do business with such a company?
The first negative thing I've heard about Radiantec. Can you be more specific? I thought there components and tubing were well-explained for quality choice etc.
I am not interested in bashing for the sake of bashing... so give me a couple of days and I'll put something together for you.
I also am looking into a first experience with radiant floor heating in an upcoming ~3100 sq foot home in Ohio. Am very interested in your comments as well.
I am planning a closed system, I don't like the possibility of condensation in the summer.
One other iem that we haven't mentioned yet...minimizing corrosion of cast iron. If you have cast iron cast iron parts in your boiler, you may want to consider a closed system.
I put in an open system in a bathroom that I renovated about 6 years ago. Until reading this post, I did not know that it was called a open system or that they were even permitted, for exactly the reason you are concerned about. My solution to the stagnant water problem was to install three three-way valves. One under the toilet and one at each end of the loop as it goes in an out of the water heater. In the summer , I turn the valves so that cold water flows to each end of the loop at the hot water heater and then turn the valve at the toilet so that it is teed into the loop. Everytime the toilet is flushed the loop is also flushed out. In the winter, I turn all the valves the other way so that hot water flows through the loop and cold water flows directly to the toilet. This works well for two reasons, first the flushing of the tubing is often enough to keep the water in it fresh without any pumps or timers and second, the flushing water does not return into the system or to any drinking water outlets. I personnally do not want to drink water after it has passed through all that plastic tubing and that may have been sitting there for a while. Another option may be to connect it to the outside spigot so that the loop is flushed out when you wash the car or water the lawn. hope this helps.
I have a Radiantec system that I installed in my home in Castro Valley, Ca (I know we do not need a whole lot of heating). It is an open system and as a homeowner I love it. All the water for the house runs through the hydronics first so there is no possibility of stagnation. In the summer our landscape system keeps it flowing and cool on our feet. In the winter with the flick of a valve the incoming cold water is preheated by water from a tankless heater. I have a storage tank (I know defeats the purpose of a tankless water heater but saves a constant supply no matter what we are using in the house) set to 140 degrees. The tankless water heater is set right in the middle of its range. We are never burned, never scalded, have cozy showers (which have their own anti-scald valves anyway) and the temp gauges for the hydronics show 100 to 120 when the heat is on.
An open system just made sense. Water is pre-heated, summer keeps the floor cool and the only thing I have to do is move one valve seasonally.
If there is ever a discussion of radiant heat versus anything else count me in. I see no comparison.
So when you read the bash about 10 messages ahead use your own judgement. I have the facts that worked for me. I like your "tradition" statement. Anything new could bring problems to a professional later so of course they will tread very litely on innovation and change.
I'm tickled to see your post. So many of these have discounted the open system, and particularly Radiantec. I am also planning on using their system, and have thus far been pleased with their materials and assistance.
I have been interested in the business of having an outdoor reset device, as here in the Colorado mountains it is cold. do you have experience with that?
Did you have any difficuoty during the installation, in particular pulling the tubing through the joists, and nailing up the aluminum plates?Our house is big, and 300-400 foot runs of tubing will be the rule.
Also, did you use their Polaris heater? It seems to meto be a quality product.
Did you use their system of just thermostats to control the pumps, or a more sophisticated controller system?
Looking forward to your response.
By the way, if you prefer, my email is stefs@direcway.com
STef
I bet you have long since installed your system so you have your own answers. Sorry I dissapearred.
The pulls were accomplished with three guys and some incredible timing on the push/pull. The aluminum plates flew up. Our tankless is a Bosch (their biggest size-not the Home Depot version). We did cheat with a holding tank so it is not exactly "tankless". We have had two showers, dishes at the sink and the wash going with absolutely no pressure or heat problems.
We do have a controller. We also have 8 zones. I know total overkill, but we like the bedrooms cold. I am not sure why Radiantec gets badmouthed. Their service has been perfect-technical and otherwise. I have seen reviews for some of the other companies that complain about fittings. It is suprising how well DIY can accomplish a job with a litlle research..... very often contractor complaints have nothing to do with the performance of the product....but that is a whole new discussion thread.
Just make sure when you finish you take time to appreciate the absolute advantages of hydronic heating. Quiet and Warm (not hot, not drafty)!
As a former customer of the company you mentioned, I have found other suppliers that can solve your problems. I am based out of Florida, do most of my work in VA, and WV. I use a supplier out of Pittsburgh, PA. I got the WIRSBRO book on radiant heat systems. The book is written for the pro but with some work you can get through it. I only install closed loop systems. I am on my 7th system in three years, and have had great results. If you are heating any sizeable area I would think that you would want to go with a different boiler for the RH instead of using a hot water heater. The nat gas boiler that I use is 98.3% efficient. Most of my customers live in an area the has freezing temps for some period of time, hence I use a glycol mix in the RH system. Imagine an ice storm that causes a three day power outage. If you don't empty the system you could end up with a mess.