Question: Are there any specific clearances for a Fischer stove or must NFPA guidelines for generic stoves be used? Also- is there a problem with using an 8-6" reducer for the stove? The stove flue is 8" and the metalbestos chimney is 6". If there is a problem are there any alternatives other than replacing all of the existing chimney pipe? Thank you. Answer: You must use the NFPA Guidelines for a stove like this. According to code- there is no other alternative than replacing the chimney with a larger one. The door size- firebox size and stock temperature of that stove were matched to an 8" flue. Reducing to a 6" could cause a lot of problems.