Venting gas water heater, oil furnace, and wood stove into one chimney

Home Maintenance Questions and AnswersCategory: House ChimneyVenting gas water heater, oil furnace, and wood stove into one chimney
Question by JohnnyW

Hi.  I have a chimney with multiple flue pipes running through it.  There is one from a forced air oil furnace and one flue from a natural gas water heater.  I want to know if it is safe to run a third separate flue pipe for a wood stove fireplace insert in the same chimney.  I’ve heard this can be a fire hazard because of potentially combustible gases in the exhaust of the natural gas water heater and the oil furnace.  Does anyone know anything about this.  I would very much like to use the wood stove this winter as it is a cheap source of heat.  Thanks.

1 Answers
Dariusz Rudnicki Staff answered 1 year ago

Hi Johnny,
I wouldn’t do anything without contacting a local Certified Chimney Sweep (, just to make sure that your other two flues are in a good shape, and to ensure that whatever you’re doing complies with a local code.
Since you can vent multiple appliances into the same chimney for as long as different types of fuel haven’t been mixed / you’re using separate flues for wood burning, oil and gas, relining of the original fireplace chimney (your new insert would most likely require class “A” chimney which are designed to withstand a 2100 degree chimney fire for 10 minutes) might be possible.
The height of all flues might need to changed so the house negative pressure will not pull the smoke from one flue down into another located right next to it – please let me know how this ended,

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