We are strongly considering our first woodstove purchase, a used Sierra 4700 insert. It is in excellent cosmetic condition but my biggest concern is that it has been burned for the duration of its existence without any chimney piping whatsoever and its recommended pipe size is 6 inches?? We were concerned mainly about combustor damage and two, that a 6-inch pipe is too small for a stove of that strength as it will be going in a two-story 2200 sq foot colonial style home. From this attached picture of the stove fire box ceiling, can anyone tell if there is damage? I see a crack