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What material works best over radiant floor heat

10 years ago

We are building a new home with hydronic radiant heat in the basement and first floor. In the basement it will be embedded into the concrete slab. We're not sure about what to do on the main level. We would like hardwood, but what really are the best most cost effective options?

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Comments (12)

Annie Deighnaugh
10 years ago
We ended up not going with that except in the bath where we have ceramic tile over top...mainly because of the damage the radiant floor heat can do to flooring. It can be used with carpet on top, but it lowers the efficiency significantly. I know they say you can do hardwood, but I've seen engineered wood that was damaged by the radiant heat. Problem is a lot of the stuff they call hardwood today really isn't and it may not also be dried correctly, so in your house with heat underneath, gaps will open up and the edges may no longer be even. We put in vinyl flooring and the concern was that the radiant heat would dry up the glue and the vinyl would come loose. So AFAIK ceramic tile or stone is the best.

This is speaking only from what I observed when we were building a few years ago and making materials decisions. Maybe others have real life experience and can speak to it.
mrspete
10 years ago
Carpet is a possibility? I would've thought that a fire hazard! I think I would only use this with tile.
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Since you have chosen warmboard over gypcrete, what was your reasoning behind it besides responsiveness? I am sorry for the confusion. I didn't build a house with Warmboard, I had it in a house where original owner had installed it. It wasn't a house I built. I used it in the sense that I heated the house with it. I looked at the Gypcrete system and somehow feels uneasy about it. Doing a concrete pour over first and second floor does not sound structurally sound to me. Gypcrete has positives and negatives but shouldn't be overlooked because of structurally sound. I think a competent and knowledgeable designer is much more important than which type of system you use. So if you don't have a lot of experienced local people, you have to find experienced people who can help design at a distance. I would start with Radiant Engineering (talk to many companies though). A long somewhat unbiased discussion of radiant: First, it should be noted that radiant heat isn't an efficiency discussion. As people have pointed out many times hydronic radiant systems rarely have a positive payback. They are simply too expensive to install and they never payback if you are installing central air. However, every decision in your house isn't about payback. There are many decisions, such as paint color, cabinet color, cabinet design, many fixtures, etc., that are about your enjoyment of your home. No one has a pool installed because they want it to add value to their house. Radiant fits soundly into that category. Next: A discussion of trade-offs between the different systems. It is important to note that ALL radiant floor systems will provide a comfortable environment to a home that other heating methods struggle to achieve. There are basically five considerations in radiant heat (1) installation costs, (2) operating costs, (3) responsiveness (4) allowable customization and (5) noise (as hot water passes through cold aluminum plates it makes noise). If we look at the different systems we can typically see how they handle each of these things. Warmboard is (1) very expensive to install, (2) it has a low operating cost as it is a warm water system rather than a hot water system, (3) incredibly responsive for radiant heat (able to heat a structure in hours rather than days), (4) low customization and (5) low noise. Underfloor transfer plate systems are (1) moderately expensive to install, (2) low operating costs as they are also warm rather than hot water systems, (3) are somewhat responsive (4) highly customizable and (5) have more expansion noise. Gypcrete overpour is (1) moderately expensive (still cheaper than the two above), (2) have low costs as,they too are warm water systems, (3) not responsive at all, (4) are highly customizable and (5) eliminate almost all noise. Staple up systems are (1) pretty cheap (2) high operating costs as they are a hot water system, (3) not responsive at all, (4) limited customization (they are more limited by physics than design), and (5) are pretty noisy. So looking at Warmboard vs. similar systems - the only real concern from using any aluminum covered plywood system is the noise. Warmboard eliminates expansion noise because of the "special" glue they use to adhere the aluminum to the wood. I can't really tell you how special their glue is, I feel confident they will say super special and their competition will disagree. Warmboard type systems vs. underfloor transfer plate systems - Warmboard is quieter but the loops are not really customizable. Loops are 8" apart with Warmboard, so you can choose not to put warmboard in places but you can't get the loops closer together. With transfer plate systems you can customize the heat of a room by simply moving the loops closer together. This means that you can make the floor right outside the shower warmer than the floor beside the toilet (not many people spend a lot of time standing beside their toilet), but there is more expansion noise. Warmboard is a bit more responsive than transfer plates. Warmboard vs, gypcrete overpour - Gypcrete overpour gives you almost unlimited customization without the noise associated with aluminum transfer plate systems. However, it is not at all responsive. Staple up systems - They are more expensive to operate than any of the above systems but are cheaper to install and easier to maintain. You are not likely to nail through a staple up system with a nice thick transfer plate. Also easier to remodel with staple up systems. TL:DR In the end, if I was ranking a radiant system today - I would probably rank it - underfloor transfer plates > gypcrete > Warmboard. But it is a three way photo finish so it wouldn't take a lot to change the order. Also noisy houses don't bother me at all.
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Glad we now agree that 85 is an established threshold that radiant floor designers use as a recommended maximum for floor surface temperature. Foot contact with the floor makes the second way high temperatures lead to discomfort. 85 is evidently too hot for those expecting warm feet and will definitely lead to uncomfortably hot room temperatures, in efficient homes. There still seems to be confusion regarding water temperature and floor surface temperature. The temperature of the floor surface will be lower than the water temperature in the tubing. The water temperature entering the tubing loop from heating appliance, will be warmer than the temperature exiting loop, on its way back to the appliance to be reheated. The only mention I made of water temperature was that 125 seemed too high for an efficient home. Perhaps not for a long tubing run with short spacing but I still think it seems high and engineers generally don't like long tubing runs. I've personally installed tubing on a spec of mine and for other builder friends. We installed short runs with wide spacing for better zoning and they were for efficient envelopes. Few ended up being hooked up to an actual appliance. Why spend that money when the required AC can handle the heating too. The "at" which I corrected to "near" room temperature comments were in regards to floor surface temperature, which is a widely accepted fact for those involved in efficient construction. From All About Radiant Floors: "Why isn’t my floor warm? Homeowners who look forward to walking barefoot over warm floors are often disappointed by homes with in-floor hydronic heating. That’s because these floors are rarely as warm as most homeowners expect." From that article's case study (keep in mind difference of water temperature and floor surface): “On the design heating day [the coldest day of the year], the water flowing through the tubes in the floor will only be at 85 degrees,” said Robb Aldrich, an engineer at Steven Winter Associates" From energy expert Alex Wilson's article describing a level of home performance between passive house and international code minimum: "in a highly insulated house (and I’m talking about a really tight house with at least R-40 walls, an R-50 ceiling, and triple-glazed low-e windows), such a tiny amount of supplemental heat is needed that a radiant floor needs to be kept no more than a few degrees above the air temperature—or else overheating will occur. If a concrete-slab or tile floor surface is maintained at 72 or 75 degrees, it will likely feel cool underfoot—since it’s at a lower temperature than your feet. So you may not get that delightful benefit of a warm floor surface.
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Do you need ROOM heat or do you want "warm toes"? If you need to heat the entire house using in-floor radiant heat (I'm assuming you are going with hydronic?) then the best option is always concrete, tile or stone. They offer the least resistance which means the most amount of heat pours through them and into the house. If you want warm feet (because the rest of the house is being heated by a fully operational forced air or baseboard heat system) then you can have engineered hardwood as a lovely option. There are SOME engineered hardwood floors that allow it being used over hydronic in-floor radiant heat....but do NOT count on it being "OK" with every engineered product you look at. And if you go with hardwood, you do NOT want to used underlayment or soft underpad with the heating system. The underpad will block quite a bit of the heat, creating excess load on your heat system (in essence you are heating the pad under the floor while the room remains chilly). Carpet is an amazing product when used with in-floor radiant heat. Carpet breathes nicely. And the underpad is the thing that has to have the "hydronic heating" allowance which means you can choose the pad that is best suited for your situation. The other thing to be aware of with wood and in-floor radiant heat: low humidity. In-floor radiant heat is KNOWN to dry out wood flooring products. Because the wood is SOOOO close to the elements, the first thing that heats up (and dries out) is the wood. To combat this issue, you MUST add in humidity control in the home. That means you will need a system (separate from the heating system) that has the ability to add/subtract humidity throughout the year. In Montana the outdoor humidity is often very low to begin with. If you then decrease it even more with a dry heat, then the interior humidity levels can be extremely low. And wood does NOT like that. A wood floor requires humidity to "sit" around about 45% all year round. Please check your building specifications to find out HOW you are going to add that humidity to your home. And then find out if you have the ability to change the humidity levels with the touch of a button (humidistat). This usually involves a system with heating/cooling ducts so that moisture can be added to the air in an even way... For right now, I would assume you HAVE to go with tile/stone/concrete until you find out the HVAC humidity control system that is currently in place for your build.
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lazy_gardens
10 years ago
Tile, cement or a well-acclimated hardwood with low thermal expansion.

A lot depends on the usual temperature of the floor.

If we build "dream house" it will be tile or (if the finances hold) mesquite.
ontariomom
10 years ago
We are doing in-floor heat (hydronic) throughout the house. Our flooring will be engineered hardwood for most of one level, carpet for the upper level, carpet over concrete in basement and ceramics in the baths. All is acceptable if the hydronic in-floor is done properly (or so we have been told). Once our flooring and in-floor is complete I will report back if we have any problems. We will be using a thinner carpet under pad that is recommended for in-floor.

We have used Uponor products. They are quality products, but Uponor does like to encourage their contractors to oversell to their clients in terms of fancy and abundant controls, pumps, thermostats, etc. The controls, our original contractor installed, are utter over kill (think space ship controls) for a residential application (apparently Uponor trainers sold him on them). We were not consulted unfortunately as to whether we wanted Toyota controls or Cadillac controls and hind sight is 20 20.

Best of luck,
Carol
Annie Deighnaugh
10 years ago
Mrs Pete, the in floor heating typically doesn't get that hot...it stays warm. It runs about 80-85 degrees which should not be a fire hazard.
cpacker
10 years ago
I have this dilemma also. Neither my architect nor my
builder have had much experience with in-floor heating.
Architect, who likes engineered wood, checked with
heating contractor who said engineered wood will work
fine. Builder thinks engineered wood is inferior product,
period. With a fixed-price building contract signed,
this decision is still TBD.
dabunch
10 years ago
I cannot help you with an answer re the type of flooring, but I can attest to the fact that IMO most engineered flooring is JUNK. Maybe an engineered floor that would run $12/sqft may work, but the typical 2 mm wood top is worse than some of the laminate.
mrspete
10 years ago
AnnieDeighnaugh, It's not that I disbelieve you, but I don't think I could "feel safe" with my carpet being heated up to any temperature! You know what I mean . . . knowing vs. feeling.
ontariomom
10 years ago
The engineered flooring we chose is very high quality. It is 3/4 inch (2 layers not multi-layered). The top layer is very thick and can be sanded down more than once. In other words, you can get high quality engineered flooring too.

Carol
cpacker
10 years ago
More thoughts on this: My radiant system will be Warmboard,
which includes the subflooring. I'm concerned with getting
maximum heat transfer, so it figures that I would want the
thinnest flooring on top. I went to Home Depot to get an
idea of what my options are. In a given finish style,
products are 3/8", 1/2" and 3/4" thick, the latter being
solid wood, favored by my builder. But they all carry
the same 30 or 50 or 55 year warranty. Is there any
reason why I wouldn't be happy with a 3/8" product?
cpacker
10 years ago
More thoughts on this: My radiant system will be Warmboard,
which includes the subflooring. I'm concerned with getting
maximum heat transfer, so it figures that I would want the
thinnest flooring on top. I went to Home Depot to get an
idea of what my options are. In a given finish style,
products are 3/8", 1/2" and 3/4" thick, the latter being
solid wood, favored by my builder. But they all carry
the same 30 or 50 or 55 year warranty. Is there any
reason why I wouldn't be happy with a 3/8" product?
robo (z6a)
10 years ago
There is no way hot water heat could be a fire hazard. It is much less than the temperature of boiling water! Even the most flammable of gasoline soaked carpets would have to be around 500f to ignite.

We have hydronic heat under regular maple hardwood (15 year old system) and it is zero problem. Your mileage may vary depending on your system, but think of it this way -- the water under our floor is like max 100f (the floor only gets up to 80f), and our house gets close to 100f on the hottest of sunny days (no AC up here in Canada although I came close to the breaking point this summer). So I can't really see how the heating is more harmful to the floors than everyday life.

Slightly related: my uncle was chiding me for the 'safety hazard' of letting my curtains drape over my hot water radiators. I was like 'What are they going to do, slightly warm my curtains to death like a gentle beam of sunlight?' Well, I was more polite in person. But seriously.

This post was edited by robotropolis on Mon, Nov 25, 13 at 22:41

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