I can only answer this based upon my own experience. I have installed in-floor heating lines only once but I did some research and here is how I did it. First of all I laid out a product called insul-tarp under the concrete which is said to have an R-Value of 10. Next I placed the heating lines at 9” intervals throughout the basement with the first line 6” from the outside wall and the second line at 9” from the first. This provides a little more heat in the area where it is needed more. Another tidbit I discovered in my research was that I should not run the heating lines too close to the toilet as the heat could melt the wax ring. I used 3/8” rebar at 18” squares and twist ties to attach the lines above the rebar. Finally I placed the lines about two inches into the four inch concrete

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