by Hearthman on Thu Feb 18, 2010 10:51 pm
Warren, you didn't provide much info. so I'm not sure what you're dealing with or asking. Are you saying the AHJ wants you to install a B-vent in lieu of a listed liner in the chimney or is he asking you to use B-vent as a vent connector to the masonry chimney?
You must also consult the mfrs listed instructions. Some furnaces require a B-vent connector even in a conditioned space venting into an interior chimney. The codes and mfr much be consulted for specifics in vent connector sizing.
Modern 80% fan asisted furnaces run on such low stack temps, there is very little heat lost to warm the stack and thus create draft. The use of B-vent prevents stack connector losses, which helps draft while reducing condensation of flue gases. If this furnace does not have a post-purge cycle, one can easily be added, which will purge much of the moisture out of the stack and reduce condensation.
Is there a gas water heater common vented with this furnace?
Hearthman
Keep the fire in the fireplace.