Expert: James Ball - 4/21/2009

Question
Hi...I am currently having contractors give me quotes to replace my old gas furnace.  I have a cape cod house with a brick chimney within the house (only like 4 feet stick up above the roof) that vents a 25 yr old gas 100,000 BTU furnace and a 15 yr old 40 gallon gas water heater.  Since I'm going to be replacing the gas furnace with a power vented 96% model...I have had contractors tell me that I would "have to" either also replace the hot water heater with a power vented unit and seal off the chimney OR I would have to reduce the flu size to accomodate the exhaust only coming from a gas-fired hot water heater.  Recently, I had a contractor tell me that I wouldn't "have to" change the chimney flu size since the chimney would stay warm with just venting the gas-fired hot water heater.  He said since the majority of the brick chimney is within the building it would stay enough.  So...my question is what would your opinion be about leaving the chimney venting the gas-fired hot water heater and just use mortar to seal up the old vent hole for the gas furnace?

Answer
Hello Andrew, a 15 year old H/W Heater might need replacing too? and at this point I would to the ventless.
you chimney might not be the right size to handle just the H/W Heater and with an insulated liner and new hot water heater it should be cheaper to install the direct vent H/W Heater.
You could have a local Certified Chimney Sweep (www.csia.org, there you can look up by zip code to find one near you) take a first hand look at what you have they should be able to help.