I am doing a chimney install and need to air seal around my cathedral ceiling box. Can I use this product? http://www.touch-n-seal.com/gunfoamII.htm I plan on running double wall pipe (DVL to Double wall chimney) for the span and the my cathedral ceiling is 15 feet above my stove. The stove will run into the cathedral ceiling box. I want to air seal around the box. What type of external temperatures will the box have? My main concern is the polyischonerate that is near the box. I am insulating below my rafters with a layer of polyiso. Polyiso is very flamable. Is there some kind of insulation/firebreak that I can put around the box above the drywall and below the roof deck?