Gas furnace flue tied in to chimney

[JIM MURPHY]

Older home, 1940 has gas furnace flue tied into the chimney on a separate flue. Another way of saying it is that the fireplace has a flue and the furnace has a flue both exiting the top of the chimney. Are there dangers here from CO2 leakage? Is this correct? If not how would you word it?

Jim

[Bob Harper]

The furnace and fireplace must vent into separate flues that each are suitable for the class of service. The standard to make this determination according to the NFPA is a Level II inspection, which takes in the entire chimney as well as flues and attached appliance venting.

I'd worry more about CO than CO2.

[JIM MURPHY]

Thanks Bob, that was the answer I was looking for. I meant CO.

Jim