Venting Furnace and Wood Stove into Same Chimney

Home Maintenance Questions and AnswersCategory: Furnace VentingVenting Furnace and Wood Stove into Same Chimney
Question by David

I have a 78% gas furnace in my basement venting up my existing chimney. I would like to use the chimney to also vent (on a seperate vent line) a wood stove insert. Both flues would occupy the same chimney cavity. Would the heat from the wood stove negatively effect the draft from the gas furnace? If anything would it not keep them hotter and insure up flow?

I am going to consult a local professional, i’m just curious as to if it even is feasible.  Secondly if i need to re-vent my furnace, is it possible to side vent a 78% gas furnace with a blower connected to the furnace switch?

1 Answers
Dariusz Rudnicki Staff answered 8 months ago

Hello David,
As long as you have two separate and properly sized / installed flues (make sure that you use proper type of material, especially for the wood burning stove flue, which would most likely be a stainless steel pipe ) within the same chimney cavity, you should have not problem. Building and safety codes only forbid venting different fuel type appliances into the same flue.
 
You also have to remember that for the wood burning stove your chimney should extend 2 feet above anything within 10 feet or 3 feet above roof peak (regular furnace chimney might be sometimes shorter). Running both of the appliances at the same time (since the wood stove would produce much more heat) will most likely improve the furnace flue draft, but with a properly sized furnace flue, there’s no such need / don’t burn wood just to increase the flue temperature.
 
Re-venting through the side wall (I understand that you currently have a natural draft furnace) assuming that your jurisdiction has nothing against it, could be done. Your furnace (like you mentioned) would have to be retrofitted with a proper size / type induced draft motor, and this is critical for your own safety.
 
I would start from calling the furnace manufacturer and if they and locals approve it, hire a licensed HVAC contractor to do it. In Illinois this is much easier – it’s simply not permitted …

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