I am installing a radiant heating system by attaching Pex pipe to the underfloor of my bedroom, which is over the garage. I’m using aluminum heat transfer plates, which cover and hold the Pex in place.
What is the best way to insulate the nine-inch joist space in the garage ceiling, which is the space right below the heat transfer plates and Pex? Also, does reflective insulation serve the same purpose regardless of which way it’s facing?
Your application is one that is an ideal one for a reflective insulation or radiant shield. You could attach the reflective material to the face of the floor joists with staples. The heat that is generated by the radiant system that goes down will be reflected back — not passing through the shield.
Generally, I suggest you use a reflective material that has 2 reflective surfaces, however, if the one you choose only has one, it doesn’t matter which way it faces. I hope this has been helpful.