Here is the situation I wrote about with the Thermafiber Safing Insulation good for up to 2000 deg. in the thimble and the R30 surrounding it in the thimble frame. What do you guys think? According to person I spoke to at the chimney manufacturer this is ok but I'm not sure because the R30 is squeezed into the thin spaces of the box so the R value is diminished and I have read some questionable things about excessive heat and regular insulation such as the resin in the insulation dissolving around 300 deg. and not to put insulation near chimneys. The square cutout that you see in the picture is a little bigger than the actual frame that you don't see behind the insulation.