Question: I have a Fisher Stove with an exterior flu pipe that measures approx. 9.25" in diameter. There is another pipe inside this one that is only a little smaller that I assume creates an air space. I need to replace a 3' section and the top cap. CAN SOMEONE PLEASE HELP Answer: That is probably not enough information to get a replacement part. The chimney sounds like class A double or triple wall, but there have been at least 10 brands. Best bet is to remove a piece and bring it into a knowledgeable retailer. If it uses air to insulate...most popular brands are Dura-Vent and Air-Jet If it uses packed insulation, it could be metalvent, metalbestos, security or others. However, most of the double walls are only 2" bigger than the inside diameter - i.e. 8" on the outside.