I have one great idea how to make a warm floor in my bathroom using running hot water. So... from the boiler to the shower i am going to put the hot water pipe in the floor, cover pipe by metal grid and a concrete and tile. So, while I get a shower my floor is warming. I have just a doubt what kind of pipe to use for this? What thikness of the concrete layer to use so that is not hot for feet? What is the best way to lay the pipe?