We are getting ready to pour a new concrete slab over top of an old slab where a house was demolished. The old slab is 4-6 inches thick, and the new slab will be 3-4 inches thick. We would like to run PEX lines for a hydronic radiant heat system in the new slab.
From the research I have done, everyone says to use insulation under the slab to prevent the heat from going into the ground instead of into the house. I am wondering how critical that is and how much it will affect the efficiency of our system since we don't have the option of putting insulation under the slab. Should we abandon the radiant heat idea?
Any advice is appreciated!
Best Answer
If you want to do radiant infloor heating you will need to insulate under the slab. If you don't you will constantly be rejecting heat to the ground underneath the slab, and it will suck excess heat out of the system. If your not going to insulate beneath the slab, abandon the idea of radiant infloor.
Your also going to have to use HE Pex for radiant infloor. Standard waterline Pex is not allowed for hydronic heating systems.