I am looking to replace my gas insert with a woodburning one since I get wood for free from my land. The question I have is currently the gas insert Clayton CLAY-40GI has a 4" flue and 4" flue flex pipe. I see that the C550 has a 6" flue. Is it acceptable to use a 4" flue pipe with a reducer on the flue opening on the Jotul? It would save alot of money to just re-use the existing flue pipe and not have to re-run the 6". If it can't be done for safety reasons I can understand. Thanks.