My house was built in 1920 in Providence, RI.

I'm not sure of the design of the entire chimney, but the water heater and furnace vent into the chimney. I am considering using a Chimney Balloon, but it would need to go above the damper since there's not a good surface to install it below the damper. Would it be likely that I'd block the ventilation of the water heater and furnace by installing the Chimney Balloon?

  • I'd love to hear whether your chimney is actually one flue or more. Commented Nov 22, 2015 at 13:22
  • @DanielGriscom we had a chimney sweep inspect, and it turns out there are separate flues for fireplace versus heat and water heater. Not sure if it is two or three flues total though.
    – Mike Eng
    Commented Jan 20, 2016 at 22:58
  • So, looks like you're good with the balloon. I'd still be cautious, though. Commented Jan 21, 2016 at 0:11

1 Answer 1


You should check whether there's a single flue for all three utilities, or multiple flues. Generally (and I think this is code, at least in the USA) fireplaces shouldn't share their flues with anything else, including other fireplaces. My (1960 Massachusetts) house has two fireplaces, a furnace and a gas hot water heater; it has one flue for each fireplace and a third shared flue for the heat and hot water. If they're separate, then you don't have a problem.

If indeed a single flue services all three, then you'd need to find out where the furnace and water heater's exhaust join the flue. More importantly, I'd be worried about safety even without the chimney balloon; it would be easy for carbon monoxide from the water heater and furnace to come down into the fireplace and into your living room.

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