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!