[defed]

i emailed the mfg to see what they say. i know that the stuff melts/burns under direct flame, just wasnt sure about indirect heat. the 'iso' foam can withstand more heat than the regular polystyrene, but still probably only 300F max.

since the sheets are only 1.5" thickness, and i have 3.5" wall, worse case i will put some 2" high heat insulation on the 'heat' side, and the foam on the outside. i really doubt that 2" mineral wool will be anywhere near 300F on the outside.