To reduce the energy costs of operating the heated floor the slab should have 2" foam under the cement and the walls to be insulated to R-19, ceiling to R-38, door to be exterior grade and weather stripped.
Installing an electric radiant heating pad on an old concrete slab floor.
I should have mentioned that the concrete slab is part of an old breezeway that I am rehabbing. It had asphalt tile on it for about 50 years, and this is now removed. Therefore, I cannot put any insulation under the slab. What kind of insulation can I put between the top of the slab and porcelain tile? I have heard of cork insulation. Is this a good choice?