wood over warm floor

archibald tuttle

This issue has no doubt been discussed at length, in fact I may have participated. But given that I am about to do another project where this is an issue I would like to again plumb (sorry) the depths of knowledge here on either the emperical or theoretical plane.

I have several thin slabs of lightweight concrete over wooden subfloors in upper floors of homes running. In these installations I avoided using another layer of subfloor and rather laid sleepers every 16 inches and secured long tongue and groove flooring pieces directly to the sleepers on the theory of not creating even more resistance to the transfer of heat from the mass to the living space.

In the present job the finish floor is a tropical hardwood, very dense and 5/8 inches thick. My flooring subcontractor suggested installing a subfloor over the sleepers and warm flor mass (1 and 1/2 inch thick)in this case because the flooring pieces are short and random length and unsuited to insuring that they join over a sleeper as I have done in the past.

I could increase the frequency of sleeps to 12 inch spacing or even 6 inch spacing in order to avoid using a subfloor, but the flooring sub insists that my aversion to additional thickness of wood (and the tiny but relevant air gap between the subfloor and finish floor) is misplaced since all the heat in the floor will eventually arrive in the space, and the main issue will be slowing response to outdoor chilling. The house is pretty stable and there is a heated basement slab 10 feet below this floor. The heating of this floor is mostly to add responsiveness and 'finish' level comfort. During construction last winter the basement floor was the only heat for this space and it was quite comfortable to work in.

It is also possible simply to give up on my affinity for mass floors and look into placing floor heating pipes on the underside of the main subfloor rather than in lightweight concrete on top of the main subfloor. This could be done with or without the aluminum heat spreading elements.

If I add thes aluminum pans in, I don't think I really save any money by doing it this way but it does give me a wooden subfloor to attach the flooring to so it perhaps it saves me the plywood costs of an additional subfloor if I were to employ one.

I have never installed two layers of wood over a warm floor. I have helped friends do the joistspacing install from underneath with pans in a couple of old houses. I think they have been reasonably comfortable with this system and I know several other plumbers who have installed like this in new construction without aluminum pans and they are still in business and don't appear to be plagued with complaints from the better business bureau.

So, perhaps my penchant for mass and as little wood as possible between radiant source and living space is misplaced. Would appreciate any current emperical or theoretical dissertations on this subject (including pointers to useful older threads or, god forbid, non heating help sources on the subject).

Thanks,

Brian

Josh_10

An inch and a half of wood over the top is too much. According to my calcs you are looking at a supply water temp of 157 degrees.

Not sure what the degree days are like in your area so I am making assumptions. You would have to run some pretty high water temps. Can you run some simulations in a heat loss program like Wirsbo ADS 6.0? I would.

By the time your contractor installs all of that wood you could have purchased a Raupanel system. If you haven't looked into it I would. Here is a link

http://www.rehau-na.com/construction/heating...plumbing/radiant.heating/raupanel.shtml

Paul Pollets

Radiant flooring guide

here's a link to the radiant flooring guide, developed by the RPA. It's a complete primer for what to do:

http://www.bnpmedia.com/digitalmagazine/index.html?pub=RFG&iss=2006

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