All I know is that the floor feels great on my cold, old tired feet. . . . This is only phase #1 1800 sq ft in 2 zones of 900', with 1800' of 1/2" pex 1' a part and 200' of 3/4" pex. I'm oversized for this stage @140,000 btu. Phase #2 is DHW for shop and house. Phase #3 is 1000' of staple up...