Stewart Devereux wrote:

We have had numerous wood burners over the years, some with similar
problems to yours. First you must be aware they can generate ALOT of heat,
so metal might not be the best idea. I would go along with first reply.
1-2 inches loft insulation pinned to brick, then cut a piece of fireboard
to size and cover. Can easily be painted matt black. The burners work best
by allowing air to circulate around them-I don't think once you have it up
and burning you will be worried about reflecting heat back in !


Thanks for the reply, and to Andy too.

This one is a tiddler, and only 4kW. Nonetheless, I agree it should put out
a lot of heat.

One installer told me they could not put it in without enlarging the
aperture, because all the heat would get absorbed by the brickwork and none
would come out into the room.

Another installer (the one I want to use) said that was true, but he
proposed to use a 90 degree elbow from the back rather than the top, and
put the unit 3/4 way out of the hole, so only 1/4 of it is inside the
aperture.

That is really why I was thinking about the reflective qualities of the
backing, but I guess with a stove obscuring most of the opening,
re-radiated or reflected heat from the backing is not going to make much
difference.