Wood Burning Furnace

This is the first time I have seen a wood burning furnace. It was connected the natural gas furnace. It had a blower & filter.
They installed a chimney liner and the wood furnace was vented up the same flue.

The gas & wood furnaces shared the same return & supply ducts.

I told the client to have this archive removed and then a HVAC to evaluate the system.

I have been seeing some archives this week.


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Wood and Gas can not use the same flue
Roy Cooke sr . Royshomeinspection.com

They use this wood furnace as an Emergency heating system.

When the power goes out, they load up the wood burning furnace.

Frequently, the wood burner is the primary heater and the gas (or oil) furnace is used when it’s too cold to go outside for more wood.

Roy is correct, the flues must be in separate chimneys–unless specified by the manufacturer. Some particular instances require the same chimney for both flues. Always refer to the manufacturer’s manual. If it’s not available, make sure you recommend it be checked by a qualified HVAC.

Use your head and think how great it is to inspect wood furnaces. In the summer or spring you can’t inspect them because you’d have to go get firewood and stroke it up - which you’re not gonna do. In the winter if its cold they’ve got a fire going and you can’t get a full or good look in the firebox or heat exchanger - so it does not get fully inspected.

Bottom line - 99.7% of the time a wood furnace gets an automatic referral to have it serviced, **CLEANED **(you just know theres gonna be creosote, soot, etc somewhere that needs cleaning) and evaluated by a competent and licensed wood furnace guru. Gosh I love wood furnaces.


I agree with the guys that say this setup needs separate flues.

The temperatures of wood burning stoves is much much higher up 500+ degrees F .
Creosote residue in a flue with a much “colder natural gas burning appliance” Is NOT recommend.

The colder burning natural gas will release a lot more moisture in the flue, maybe sweating inside the flue since the chimney sizing issues are probably wrong.

Natural gas burning appliances need (generally smaller flues) for proper operation then wood burning fire places. So end result is a flue that is too large for natural gas products of combustion to be “drawn” up the chimney.

Acid from the water combining with the creosote could be the next issue. That liner better be a good stainless steel but again we come back to the issue of two separate fuel types…

I highly recommend a complete evaluation by a CSIA tech or a similar tech.


Also check out Gamanet.org

For topics on natural gas and proper flue function. Great info for all .:smiley: