From everything I've read, a concrete slab is the best floor to collect passive solar heat. I've also read that you can cover the the concrete floor with material that will not block the heat transfer such as tiles, but that carpet would greatly reduce the energy the floor can absorb. I would like a softer more forgiving floor since we have a young child, and just for general comfort. Do you guys think that 3/8" thick rubber tiles (like commercial flooring) would allow the concrete slab to absorb solar energy? Would the dark rubber help absorb heat the easily transfer it to the concrete or would it hinder the slab from absorbing heat? If you have any other ideas for more forgiving flooring that is also good for thermal mass I'd like to hear those as well. Thanks.

You should look up the R value - but yes, generally rubber is a good heat conductor and black is good at absorbing solar energy.

Thanks for the reply. According to this http://www.sun-touch.com/pdfs/R-value%20Subfloor.pdf the R value per inch is pretty average and since the flooring is thin, the total R value for the floor is pretty low. This may well be the thing to use then. This is the kind of flooring I was thinking of. http://www.nora.com/index.php?id=4712

Different colors and different surfaces have different absorptances of solar radiation - think of black paint versus white paint. R-value is not the only consideration, and in many cases, is not the most important consideration, as surfaces can only store the heat that they absorb. Any surface painted white will have serious absoprtion issues, regardless of the R-value.

Jeff

I know this is the reverse of what you're thinking ie heat out rather than heat in. but I have a radiant heat floor (pex tube in 1 1/2" of gypcrete on wood) and it's covered with dark 1/8" thick cork tile. The heat appears to have no problem getting through the cork and the feel of the floor is wonderfully cushioned. Also looks terrific, is green, and stands up to wear (ours is 10 years old).

Re cork (or other coverings): Any R-value induced delay in getting the heat from the "surface" into the "storage" will significantly reduce the effectiveness of the storage. The heat will radiate back from the surface (via the same radiation that's at work with radiant floors) before it's absorbed into the storage, and your efficiency will go down, if not plummet outright.

Jeff

It all depends on the R value - 1/8" of anything doesn't have much.

Hey all, I thought this thread died off so I haven't checked it for a while.
Regarding the cork flooring, it certainly would work for comfort but I remember reading some material that specifically pointed out carpet and cork as bad coverings for thermal mass flooring. They both have pretty high R values. This table seems to confirm that (http://www.sun-touch.com/pdfs/R-value%20Subfloor.pdf). Now your cork tile is only 1/8" thick so maybe the impact would be minimal.
Low R values and dark coloring seem to be important factors. Are there any other considerations that I may not be taking into account? Is the general consensus that rubber tiles such as these (http://www.nora.com/index.php?id=4712) would work well for this purpose.

Thanks.