# Ducting an add on wood furnace



## phlynott (Feb 27, 2006)

Ok, I had a new gas furnace installed last november, and the company offered to "tie in" my wood furnace. Previously the wood furnace only fed 2 seperate ducts. So I thought, great, now the wood furnace will heat the whole house. Wrong!!! The installer put in a relay that kicks on the fan to the gas furnace when the blower on my wood furnace goes on. It's supposed to help circulate the heat. Well, I end up with lukewarm to cool air comiing out of the registers. And it takes forever to get any sort of heat built up. After doing some research, I found that the problem might be how my wood furnace is ducted into the gas furnace. Currently the output from the wood furnace is ducted directly into the plenum above the gas furnace. From what I've read, this setup doesn't work very well since the blower on the gas furnace is stronger, it tends to build slight pressure in the plenum thus not allowing all of the heat from the wood furnace to enter the plenum. Whew, that was a lot to say. Somewhere I read that if you duct the output from the wood into the cold air intake/return in front of the gas furnace, the gas furnace will actually draw the heat in from the wood furnace. I thought I'd ask you folks before I try anything



Joe


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## DeanBrown3D (Feb 27, 2006)

Remove the fan from the wood furnace and make the wood furnace kick on the gas furnace's fan. And take the hot air from the gas furnace into the cold air return of the wood, and exit the hot air from the wood into the house ducts. There should only be ONE plenum, on the wood side. 

When you use your gas only, it will have to go through the wood furnace before it enters the house. So make sure its well insulated.

Dean

Here - read ALL of this thread, not just the start:

http://groups.google.com/group/alt....28f1d/23f63f73987a3816?hl=en#23f63f73987a3816


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## hautions11 (Feb 27, 2006)

*wood furnace*

My wood furnace has it's own fan. I bought it used at a furnace place for $20. I had the furace place build a sheet metal box with a 14" round inlet at the bottom, goiung through a regular furnace filter. The top of the furnace has an 18" round outlet feeding directly in to the plenum above the furnace. The cold air draws from the cold air plenum on the gas furnace. I slide a piece of sheet metal in the gas furnace filter slot so the wood furnace will pull cold air from the house, not from the gas furnace plenum. The fan and furnace run off a thermostat right next to the gas furnace thermostat upstairs. It heats VERY well down to about 10 degrees. After 10 degrees you get up in the middle of the night to feed it. The down side to my set up is the gas furnace is off when the wood is running. Older 3200 sq foot house central Indiana. I would love to come up with a baffle system to block the air returns so the gas would automatically kick on if the wood ran out. Kerri is home during the day so it is not a huge deal to keep it running all the time. My camera is at work, otherwisw I would snap a couple of pics.


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## hautions11 (Feb 27, 2006)

*wood furnace*

I have never looked at that style damper, but it sounds really good. What is it that activates the dampers? Plenum temps?

My large wood furnace fan is very quiet, but I would love the ability to stoke it up at night and let it go out without waking up to 55 degrees.


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## jensen 32000 (Feb 27, 2006)

*gas/wood furnace*

Guys, check outthis site: http://www.yukon-eagle.com/testimonials.htm Sounds like a good system, Mike


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## DeanBrown3D (Feb 27, 2006)

*TreeCo*

Got a pic or 1-line description of those motorized dampers? Do they have a feedback signal to tell a controller that its working and open or closed?


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## logbutcher (Feb 28, 2006)

*"Hungry" Be Careful*

Your setup sounds like a recipe for danger. Mixing different combustors, with different air requirements, different combustion temps, etc.... does not sound too fine. JMHO. :censored: 
Your home is too valuable too fool with those non-expert specialists. And, check with your insurance company and the local fire inspector if there's one.
Our rural region has none.
I hope that you're not using a shared flue for both furnaces: gas and wood. 
Mother has spoken. - 
That guy with the cat has it right: K.I.S.S. Free standing, no electric wood stoves. Not as effecient, but...........


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## phlynott (Feb 28, 2006)

I am just looking for ideas right now, my gas furnace and ductwork are under warranty so I would have any modifications done by a contractor. I am simply trying to find a better solution to my current ducting and wondered if anybody has a setup where the wood output goes into the cold air intake



Joe


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## phlynott (Feb 28, 2006)

yeah, no shared flue, the woodburner is on the chimney and the gas is a pvc type vent, completely seperate.


Joe


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## hautions11 (Mar 6, 2006)

*My Furnace*

Here is my set-up. I keep the feed pipes from the wood furnace as short as possible. The CFM is not as good as the regular furnace, but it distributes well. The cold air feed is near the floor in the back.


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## hautions11 (Mar 6, 2006)

*My furnace*

Playing with picture size.


>


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## footer (Mar 7, 2006)

*Damper*

I have my wood stove ,home made, next to my funace, and had a custom plennum made to go up and over to the furnace plennum. Both square, or retangular. Where I tied the two together, I made a flapper on a rod hinged at the bottom with the rod extending out the back a few inches. The hinge is just a 1/2" rod with a hole drilled in the plenum at both sides so the rod sticks out. I then clamped a vise grip on the rod as a lever so you coud turn the visegrip and move the flapper back and forth. With it up, the air shuts off the wood stove so the furnace/AC air doesn't go back down the woodstove. With it down, the air shuts off the furnace so the woodstove air doesnt go back down the furnace. I the took another vice grip, and weighted the first until it would balance in either direction. Now whichever blower comes on, the flapper just moves over and shuts off the other. If both are running, it sits in the middle, and lets air flow from both.


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## hautions11 (Mar 7, 2006)

*Damper*

That's a good simple idea. I'll play with mine to see if I could duplicate that idea. I could see a balanced damper on the hot side in that straight section near the gas furnace and a similar unit in the cold air section to open when the wood furnace fan kicked on. That would let the gas furance run independantly. Thanks.

L


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## laynes69 (Mar 31, 2006)

*damper*

What i did I had a hotblast 1500 series wood furnace. Same issues with heat so I ducted the heat from the lp furnace into the cold air return of the wood furnace to run series. Then ran all of the heat from the wood furnace into the house. To distribute the heat the I have 2 wires going from the limit on the wood furnace to the lp furnace circuit board. When the temps go up, the lp furnace blower kicks on and pushes the heat through the house. Eventually if the wood goes out, the lp furnace has the thermostat up stairs to kick on at a set temp. I heat a 140 year old home with this setup. 10 foot ceilings, 6 bedrooms. House stays around 76 to 78 all winter. No air can go backwards, and the cfms are the same as the furnace,


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## 046 (Mar 31, 2006)

laynes69 said:


> What i did I had a hotblast 1500 series wood furnace. Same issues with heat so I ducted the heat from the lp furnace into the cold air return of the wood furnace to run series. Then ran all of the heat from the wood furnace into the house. To distribute the heat the I have 2 wires going from the limit on the wood furnace to the lp furnace circuit board. When the temps go up, the lp furnace blower kicks on and pushes the heat through the house. Eventually if the wood goes out, the lp furnace has the thermostat up stairs to kick on at a set temp. I heat a 140 year old home with this setup. 10 foot ceilings, 6 bedrooms. House stays around 76 to 78 all winter. No air can go backwards, and the cfms are the same as the furnace,



can you post a diagram of how you did this routing? 

thanks,


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## laynes69 (Apr 1, 2006)

*damper*

I cant do a diagram but ill explain how I did it. The wood furnace had 2 blowers on the back bottom which i removed. I cut out these holes to fit 2 8 inch ducts. The wood furnace is on the left side of the lp furnace. So the 2 8 inch ducts go out the lp furnace on the left go down the side and behind the wood furnace where the blowers used to be. I had the lp furnace limiting out so I ran an additional 8 inch duct in the side of the woodfurnace, then cut a 8 inch hole in the middle of the 2 running out of the top to help relieve pressure. I tore out all of the ducting in the house and when I put in the new, everything goes off of the wood furnace. I need no dampers of any kind anywhere in the system . As far as the limit on the wood furnace, the 2 wires go off of it, to the r and g on the circuit board of the lp furnace, with no voltage of any kind. If the woodburner is going and the house drops in temp, the blower fan kicks off, the lp furnace ignites, then the blower kicks back on. When the lp furnace shuts off if the limit of the wood furnace is in range, the fan continues to run. Whats nice about the series installation, is everything works together, and with the cold air returns through the house you get even heat. Eventually I am getting a new wood furnace and I will run an 8x18 duct off the lp furnace into the side of the woodfurnace. But until then this system will work just fine. I will say one thing though, make sure the furnace is in good working order. If the lp furnace shuts down for saftey reasons, you lose your blower. The new woodfurnace I will get would be fine if electricity goes out. If power would go out, just damper back the wood furnace. Also make sure you have a good space between the floor joists and the ductwork. I have yet to get it hot, but just for safety reasons.


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## 046 (Apr 9, 2006)

finally found the information I needed for my JUCA insert. on the JUCA site of course, buried under a lot of other info. Juca's web site has the most infor on wood burning on the WWW. 

http://mb-soft.com/juca/print/117.html

http://mb-soft.com/juca/print/index.html#tech


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## laynes69 (Apr 9, 2006)

woodheat.org is also a very good site for information on wood heat.


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## 046 (Apr 9, 2006)

yep woodheating.org has lots of good info too. loads of info there about complying with epa stds. mentions nothing about free burning air designs like JUCA. 

if you need actual wood heater ducting info follow my link above. note JUCA's site is put up for info only. if you read very long they tell you that none are available for sale. a very strange way of doing business. 

My JUCA burns green 12in x 24in unsplit wood logs with no problem. it barely puts off any smoke which is probably mostly steam. when burning seasoned wood, you can barely see smoke. 

one piece of data that is not mentioned on woodheating.org's site is size of firebox. Mine is 12 cubic feet. a large firebox translates into easier to handle/loading wood.


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## 046 (Apr 9, 2006)

Damper tutorial from JUCA's site

how it works and how to make one

http://mb-soft.com/juca/info/duct.html


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## Marco (Apr 9, 2006)

*Missed this post from it's start*

I helped a HVAC installer set up something similar to what is being described previously here. He put a mechanichal damper above the gas furnace and an electric one over the wood. When the gas is on the damper shuts above the wood, when the wood is hot enough a switch above the wood tells the gas not to start. Took a few evenings of baby sitting to set all the switches and there is some overlap when both will run for short periods together. What was trying to be avoided was "short circuit" in the system where they would loop through each other. He had mentioned that ideally you would have the gas furnace and the wood furnace at opposite ends of of your main ductwork.


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## laynes69 (Apr 9, 2006)

The juca is a different type of burner. Its good to know someone has one and it burns well, What are the burn times you get with yours? Currently I get a 6 to 8 hour Clean Burn with my usstove wood furnace. I am hopeing to get a new wood furnace that produces close to a 12 hour burn. My dad has one, its built by the amish, and it uses a secondary burn chamber to burn the wood smoke. It only burns on the bottom so the wood drops like a hopper. The Smoke goes through the hot coals and burns it. Still at 1300 dollars I am skeptical, but I am also looking for something that burns less wood. What I have now works great, but something a little better would be better.


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## 046 (Apr 9, 2006)

JUCA is a free burning system. think of it as a fire inside your normal fireplace. differance is high tech heat exchanger and high flow forced air handler. 

this is why ducting is covered in detail on JUCA site. It's designed from ground up with capacity to deliver heat into your heating ducts. 

burntime is determinded by size of logs used, instead of choked air slowing burn down. follow the load calculator to determind how much wood it's going to take for a season based upon you zip code, house size, insulation etc. 

http://mb-soft.com/juca/info/ques1.html

here's a better explaination on how juca works

http://mb-soft.com/juca/print/118.html


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