engineered floors on concrete slab - radiant heat or no?

13 years ago

Hi All -

i have been searching a lot and have not found answers to my questions. i am planning on putting in engineered wood floors in my family room. it is a large (17'x21') addition to my 1930's house. hence it is on its own concrete slab. i live in Denver, CO so we have hot and cold/snowy weather but no humidity. i am worried that the floor is going to be very cold (the room itself has a seperate heater that isnt the best) and had thought about putting the electric radiant heat mats underneath the flooring. this will almost double my costs so i really want to know if this is worth while. my goal would really be to have it as the primary heat source for the room. i have concerns that it will just heat the slab and not do much else.

is there anyone out there that has had a similair experience? is there another product that might be a better compromise - i.e. a mat that would reflect the heat that is already in the room?

thank you so much in advance!

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Comments (6)

don92
13 years ago
Are you talking about glue down flooring or floating? I will not install floating floors but the glue down is great for slabs and below grade areas, as long as there are no moisture issues. I have only put the heating mats under tile though. It does a great job.
When a client wants a warm hardwood floor on a slab I often times lay 6 mil. plastic, sleepers, ridged insulation between the sleepers, 3/4 inch plywood and then the hardwood. It takes you up 1 1/2" which is not always possible but it does give you a warm floor. You could incorporate the mats into this system.
jamesbodell
13 years ago
Do you have a boiler for heat? If so, use a roth panel over the slab with pex tubing (hydronic radiant). Do not expect the mat to be primary heat for the room.

The slab needs to have a vapor barrier laid done and then insulation, then floor.
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Recipe for disaster. Concrete is porous, and thus absorbs moisture. When wood absorbs moisture, it swells. If it absorbs enough in the lower layer, with the top layer absorbing it slower, then you get cupping. Grooving will not prevent cupping. If you don't fix that constant transmission of moisture to the wood, then you get rotting. Wide plank already moves around a great deal, even when installed above grade on a subfloor. It will expand and contract with the seasons. That's normal. The wider the plank, the more movement you get. You need to maintain constant humidity in order to minimize the normal movement in wood. If you get hot and humid weather in the summer with no AC and don't use a humidifier in the dry winter air, then your wood floors, furniture, and cabinets will swell and shrink considerably over the seasons. That is NOT considered a defect. And this is why engineered flooring was created. It's basically plywood, with thinner layers of cross grained material. That means that each layer has minimal expansion and contraction, and because of the cross layers, it's much more stable. Combine that with a polyurethane glue designed to keep moisture transmission to a minimum, and that's the only consistent tried and true way to successfully have wood floors with slab flooring. It's the only way wood flooring is done here in the South, where humidity and concrete slabs are everywhere. It works, and there is no need to reinvent a square tire and call it a wheel.
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Check out Carlisle Wide Plank Floors. The package I just received has a brochure included with step by step instructions for installation of their solid wood plank flooring over concrete slab and radiant heat floors. Selection is great, and their customer service is very helpful. There are other alternatives as well such as Richard Marshall Olde Boards, but they aren't inexpensive. Good luck! Here is a link that might be useful: Carlisle Wide Plank Floors
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Thanks, franztini, for taking time to share your thoughts. I agree with you- Warmboard is great for new construction, it would be quick solution. In your situation, you probably already have some insulation in the slab from your previous radiant heat. My slab has no insulation at all. It is desired that insulation over slab has R=19. This would require 4" thick insulation. I can't raise floor that much and would be ok with R=10 (maybe even lower). Roth panel seems as a great option for slab since it is made of insulation. Also, aluminum on top may heat floor faster. Though, for some reason, I have tough time to find contractors in NJ that have experience with Roth panels. Also, comments related to Roth panels I saw on web seem to be older. I was wondering if there were any issues with RP. The drawbacks - it may be time consuming to install (especially for hardwood flooring) and R value is only 4.5 and no additional insulation can be added underneath. Though, I would still consider if people have good experience with it. Also, there could be some additional tricks to improve insulation such as insulation on perimeter (don't know much about it). I looked at HeatPly. Because it is made of plywood, I would need additional insulation. Also, you may note it doesn't have the benefit of having aluminum on top to heat floor faster. Though it is great that it is provided with boiler and tubing. If you don't need insulation, it may work well for you. I found out that in order to insulate under Warmboard, I would need to use sleepers (rigid insulation will not work). While this will be the right way to provide insulation, this will require raising the floor level. I am taking time to make the right decision but have really hard time with it and the cold weather is around the corner.
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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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kopellimonster
Original Author
13 years ago
thank you both for your responses. i am not able to raise the floors in the room due to existing exterior doors, ceiling height, ect. my furnace is forced hot air so the hydronic radiant heat is out as well.
live_wire_oak
13 years ago
Electric floor warming systems are for floor warming only. They do not heat the room. If your slab is uninsulated, then in your cold environment your floors won't even really get warm as the heat will be sucked out through that slab into the outdoors. It'll be a waste of money. I'm really surprised that you actually have slab construction in such a cold climate. Slab requires footings to be dug down below the frost level so it won't heave, and in your area, that's down low enough that it's not that much further to do a basement. And to do a slab without insulating it is also strange.

I would not put hard surface flooring in such a situation where you cannot install the sleepers and additional insulation. Your best bet for comfortable flooring will be for carpet. The padding will give a small amount of insulation between you and that freezing cold slab.
don92
13 years ago
You are probably living on a floating slab which would require about 18" footers with a monolithic pour. There should also be 2" ridged insulation extending 24" into the room and under the slab. I install many radiant electric pads under tile and I assure you Those clients toes appreciate it. If you put enough of the product in it can help heat the room but would not be the primary heat, although it would sure knock down the need for primary.
euronj
9 years ago
This is older discussion but, hopefully, the participants still will be reachable. Don92, may I ask how high sleepers do you use and how high is rigid insulation? Only 1 1/2" floor raising sounds good. Is it with insulation, panels, plywood and hard floor or only insulation?
Wianno, do you think Roth panels provide enough of insulation? I think it has R value of 4.5. I would think it should be at least 10. On another hand, Roth panels don't allow additional insulation underneath. What are your thoughts and experience with them?
We would like to install radiant heat with maximum insulation and minimum floor raising. Though, we will need to change doors yet so raising around 2" would be ok.
Thanks in advance for you opinion.

engineered floors on concrete slab - radiant heat or no?

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engineered floors on concrete slab - radiant heat or no?

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