My BIL and I were talking over Thanksgiving about him replacing his wood stove. They have an A frame house with a too big wood stove and an 8" pipe. It goes up 3 sections then through ~6' of double wall stainless and then through the roof. So a new stove will be a 6" flue. What is normally done to have a proper draft? Pull the whole works and run the 6" all the way up or if it is reduced @ the double wall or?