Best Way to Connect Wod Furnace to existing duct

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New Member
Jul 28, 2013
Rehoboth, MA
Hi All,

Hope everyone has been enjoying the wood burning season to date...and thanks for all the past advice I have gleaned from this forum. I was hoping to get some advice on the best way to connect my wood furnace to my central duct.

I recently purchased a Harman 2500-A wood burning furnace which is in my basement. The furnace has a 1000 cfm blower and I have a separate flue. My house is new construction and there is already a furnace in the basement with all the appropriate ducting and registers.

I brought in 2 HVAC companies to give me a quote on hooking into my duct and they had 2 different approaches...i was hoping you could give some insight as to which way would be better:

1) connect the plenum of the wood furnace to the main supply trunk...down stream of my "normal furnace." This is the way I was figuring it would be hooked up as the blower would get the hot air into my supply trunk and the static pressure of the system would take care of getting it through my registers to heat the house.

2) Connect the wood furnace to the return of the existing system. Have the fan of the existing system on to pull from the return and blow to the supply trunk and though the house. This seems to me to be less efficient as I would always have the fan of the existing furnace on and it would require a longer run of duct.

Is there a preferred route with this, or does it come down to preferences of the HVAC company.

Thanks for your input!


Minister of Fire
Oct 2, 2006
Ashland OH
You want to do a parallel install. Being a new home, hopefully you have access to the ductwork. There has to be strict ductwork to combustible clearances. Unfortunately, there's no specified clearances in the manual, I would contact the manufacturer.

You do NOT want to tie the plenum of the woodfurnace into the return of the central furnace, especially with the technology of now. Damage can occur from overheating the central furnace, which is not meant to take high heat within the furnace.

With a parallel install, you want backdraft dampers installed in the system to stop each unit from back feeding into another. Make sure you burn good seasoned wood, and try not to smolder the fire. Check the chimney often and sweep as necessary.
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