I've just removed an old back boiler from our lounge fireplace. To
remove it I had to remove some extra bricks which had been added to
reduce the size of the original hole. The actual brick opening is
offset from the centre and had a row of filler bricks on one side to
reduce (and even up) the hole so that it was central.

My question is whether it's necessary to reduce the size of the opening
again for the installation of a gas fire and fire surround. The
surround will actually hide the fact that the hole is large and offset
so is it required for fixing purposes? The height of the existing
opening had been reduced by resting a row of bricks on top of two old
iron gas pipes which had been let in to the bricks on each side!

We are intending to buy one of those B&Q jobs where you can mix and
match the surround, back piece and fire itself.

Do these sorts of fires fix to the surround itself or require support
from the surrounding wall ? The sizes of the fires seem to be between
470mm and 520 mm which happens to work about right if I add a row of
bricks to reduce the hole size.

I'll post a picture if it's difficult to envisage from the description
above.

Can you get manuals for these types of fires online so that I can check
the requirements before I purchase ?

PS. I'm aware of the testing required of the chimney itself and removal
of the old metal flue used for the back boiler.

TIA

Andy.