I am considering a radiant installation for a cold (50 F) basement. My less-than-precise heat calculation indicates that heat requirement will be 30-40 btu/ft on a zero-F degree day (about as cold as it will get in a typical winter here - southern NY). I will get a more accurate heat calc from a company in a few weeks. I've done one install (in another house) previously and it works fine (better now after I took the advice from folks on this forum and insulated the joist space under the loops - 25% decline in propane use over last winter, and this winter has been colder).
My issue is that the house, built in 1980, does has an uninsulated slab. How is this typically addressed? I have about 2.5" of build-up space available above the slab, so I could put down a layer of XPS and staple pex into that; is that a reasonable approach? Is a plywood layer below the pex also (or instead) a good idea? There are precious few contractors in this area who do this, and the two I called are not interested in this (740 sqr ft) job. One made the comment (which I am seriously considering) that the cost will be very high for the sqr footage, and to go with another option (but offered electric, which I will not consider). There was an electric baseboard heater in the basement when we moved
in; our first Nov, the electric bill spiked almost $300, and I turned
it off and ripped it out. Elec is $0.15/KwHr here, so no electric
option is going to be reasonable. The house has a forced air furnace (w. basement supply & return vents), but it typically does not run because I burn wood instead (house had both systems when we bought it); the wood is essentially free. But, woodstove is on the first floor, so the basement never gets any heat. My wife *loves* the radiant heat at the other house, and really wants to do it, expensive or not; we spend a lot of time in the basement as the entertainment center is located there.
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