Question: I currently own an old Kodiak air tight installed in 1979, with a double wall metalbestos chimney with an 8" inside diameter. There is approximately 4 feet of single wall stove pipe connecting from the back of the stove to the double wall chimney at the ceiling, about 10 feet of double wall chimney through the second floor and attic to the roof, and a few feet outside of the house, above the roof. The stoves that I have been looking at, including the Quadrafire 3100, have 6" flues. Is it possible to expand the 6" flue opening in the stove to fit the 8" chimney without any draft or safety problems? Answer: No problem at all, it will work fine. In your case, there are a few advantages. First, insulated chimneys draft better because they stay warmer than masonry. Also, your chimney is located within the home, which keeps it warmer still.