In article ,
"george (dicegeorge)" writes:
Behind the kitchen rayburn is a one inch gap
then a double brick wall (no cavity).

I'm swapping it for a newer one,
so now is the time to insulate behind it.

3 inches of kingspan then plasterboard is one idea.

I wouldn't put polyisocyanurate close to a fire-based heat source.
Although most polyisocyanurate board has fire retardants added, it
still burns and gives off extremely nasty toxins when exposed to
flames, even when it has enough fire retardant to prevent it self-
sustaining a flame.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]