# attaching wood furnace to current duct?



## blacknblue#2

Hey guys new to this forum. I'm getting ready to install a wood furnace in my basement. My wife wants to pay the pros but I'm a DIY guy on everything. I have my flue figured out but I'm concerned on how to force the duct from my new furnace thru the same duct work that my current gas furnace/ac unit run through. I want to use the wood heat as my primary heat while keeping my gas furnace as a backup in case the fire goes out. Do I just tie my wood furnace duct into the end of my duct run or will that cause damage to my gas furnace if the wood furnace is forcing air through the duct work??


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## NE WOOD BURNER

What wood Furnace are you installing? And Are your existing Ducts safe for wood furnace clearances/material type?

My apologizes: welcome to the Hearth!


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## blacknblue#2

Im attaching a link to the furnace I'm installing. It should give all the details on it. I'm not sure on the duct work and what its safe for. The house was built in 2012 I don't know if that could help you pinpoint what duct work may be ran through the house. The duct work is like a compressed insulation with about 1 inch thick walls and its about 6 inches tall and about 15 inches wide. Rough guessing.

http://www.usstove.com/index.php?route=product/product&path=125&product_id=973


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## JRHAWK9

First of all, I'm nowhere near as educated on this stuff as some others on this forum.  Having said that, I'm currently in the process of doing the same thing and here's how I'm going about things.  I'm going to use a single gravity damper and a single powered damper to keep the two furnaces from back feeding each other and to also keep the ductwork open in case of a power failure to allow the wood furnace to gravity flow the hot air up to keep from damaging the wood furnace.  See below for crude sketch.

I also have it wired so that the LP system can't turn on while the wood furnace is active.  This will keep the powered damper from closing when you don't want it to.

I'm getting a 24"x10" -POWERED DAMPER- with a Belimo TFCB120-S 110V spring open/power close actuator which will be wired up to my EAC (electronic air cleaner) circuit on my LP furnace.  This circuit is only energized when the fan is on, in both heat and AC mode.


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## NE WOOD BURNER

I would definitely inspect your trunk line and the ducts that branch off it. I think the Kumha furnace manual has some guidance for required duct size and material. I opted to have my plenum made and installed when I hooked up my furnace and plenum over my fisher. The round insulated foil type ducting is not suitable for wood heat and is common on new construction now. Worth having a HVAC guy look at for safety.


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## flyingcow

Get it looked at. IMO, unless it's all hard metal runs, it might be a waste of time hooking up to existing duct work. First off, it's a safety issue that needs to be looked at. Second performance, chances are the CFM's of the add on will not work as well as original, which is usually the case. get someone that knows what theyr\'re doing to look at this. And then you can DIY from there.


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## flyingcow

I used to install Ductwork for a living. Most residential installs were not done right. generally any more than 6 inches of "flex" "slinky" was the max. Never use it as a long run. Just as a connection.


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## DoubleB

And, in my opinion, ask your insurance company what they require (or alternatively find a company that agrees with your DIY installation).  I'm having a furnace installed this summer.  I'm confident I could do it fine myself, but my insurance company requires a licensed professional to do it, and I'd rather avoid my insurance company bailing on me if, heaven forbid, the house catches fire from the furnace.


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## hobbyheater

blacknblue#2 said:


> Hey guys new to this forum. I'm getting ready to install a wood furnace in my basement. My wife wants to pay the pros but I'm a DIY guy on everything. I have my flue figured out but I'm concerned on how to force the duct from my new furnace thru the same duct work that my current gas furnace/ac unit run through. I want to use the wood heat as my primary heat while keeping my gas furnace as a backup in case the fire goes out. Do I just tie my wood furnace duct into the end of my duct run or will that cause damage to my gas furnace if the wood furnace is forcing air through the duct work??




The install manual for your new add on wood furnace should have the instructions and clearances for the installation!


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