Im getting ready to replace a 80% furnace with a 94 %. The current chimney is I think is 7" (8" outer diaI measured) bvent feeding feeding the 120,000 old furnace and the 75,000 hot water heater. Do i need to run a smaller chimney liner down the bvent to handle the 75,000 btu HWH . or what?.
I would allways on a clay chimney but had not come across this with the bevent.