Heating system should be installed first then permat. This does not impede the ability to warm the floors. The testing data showed that it took a few seconds to reach target temperature but it also took less energy to maintain the temperature-- a wash! Blanke recommends that you bond tile or stone directly to Permat. The strength of Permat increase in Point load, compressive, sheer, and tensile begins to diminish once you get over 3/8 inch between Permat and tile or stone. If the floor is more than 3/8 out of level Blanke suggests you level first.