Question: I have a zero clearance fireplace. I would like to put a woodstove insert in it. problem is my firebox in the fireplace angles off towards the back, therefore the insert doesn't go all the way in. Is it ok to have the insert sticking out about 5 inches. I could cover this gap with formed sheet metal. Answer: Only certain stoves are listed to place in a prefab fireplace. Make certain your manual says that your stove is one of these. If not, DO NOT INSTALL IT. If it is OK, then the five inches is fine. You usually do not want to close off around these (except at the damper), so air flow can continue around the unit.<p> Another good practice with pre-fab fireplaces is to line the existing chimney with a single wall stainless steel pipe. The existing piping in most prefabs is not designed for the high temperatures of a stove and is often oversized.