I have a radiant floor that was installed under my kitchen floor using the aluminium heat transfer plates. Below the kitchen is a semi finished, semi conditioned basement. I would like to insulate the floor to allow as much of the heat from the pex tubing to translate to the floor (rather than helping heat the basement). Is a radiant barrier (foil) with an airspace beneficial? does the insulation need to be installed airtight? Is fiberglass a good choice in this application? Any insight is appreciated!