Theres a condition called ``Pyrophoric carbonation``. What this is, is when a piece of cellulose material (wood and other things) is heated and maintained at a temperature of 34 degrees Celsius, that's about 93 F to you guys, after a while combustion will take place. It will eventually catch fire. In the UK we have had quite a few wooden mantels over fire places, that owners have covered over, and after a few years find they can smell something burning. It seems you guys have to satisfy your insurance guys. OK. But a non combustible sheet with an air space that will allow an air flow will stop `the wall` from warming too much.