# Wood furnaces



## johnsopi (Nov 16, 2007)

Why are wood furnace not more common? If you are looking to heat the whole house it seems that they would work better. I
have a 2 story house and the upstairs is about 2-4 degs cooler then the rest of the house. My thought was that you need your chimney thimble close to the central air duct work for it to work. This is my third year and it been working well.


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## derbygreg (Nov 16, 2007)

I looked into the Brunco   http://www.brunks.com/Bruncofurnaces.html    but since my house is a wide open floor plan, the only cool room is my first floor bedroom.

If I had a house that was not open, it is worth considering.   Imagine logs up to 30 inches long.  My Isle Royale limits me to 22" logs which are hard enough to handle.

It would be cool to see one of those furnaces in operation.  They would have to be more efficient than a boiler.


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## Lignums (Nov 16, 2007)

Allot of people have them in my family, unfortunately they say that codes are different now a days versus the old days, but I don't know.  My neighbors put one in bought to Tractor Supply, that thing takes damn near fence post size stuff.  3 feet long 18 inches around.  Fill it up once a day.


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## Stevebass4 (Nov 16, 2007)

too much work and more expensive that the top of the line HE oil burner - that said i use my insert to suppliment the oilf furnace


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## Gooserider (Nov 16, 2007)

Moved by request of the Boiler Room King  :coolsmile: 

Just to put in my two cents, I think it is because builders don't think that they would be an easy sell in a pre-built house, and they are a somewhat difficult and expensive add to retrofit to an existing house.  They also can't really be used as the sole heat source (Codes, along w/ mortgage and insurance co's  don't allow it, IMHO wisely - the "automatic" aspects of a gas or oil system are better protection against unexpected abscences...) Thus in addition to the cost of the furnace itself (not cheap, they are considerably more than woodstoves from the prices I've seen tossed around) you still have to pay for the conventional furnace and it's plumbing.

In the meantime, they didn't have furnaces back in the bad old days when wood WAS the primary heat source, and up until recently the low costs of dino-fuels made the extra work and hassle of a wood furnace not worth it for most people.  OTOH, stoves and inserts kept selling because lots of people liked to burn them for "ambiance" even if they weren't terribly interested in the heat.

Even today, it isn't unreasonable to sell a $4-5K max investment in a wood stove, given current fuel costs thats a fairly short payback period, probably well under 5 years.  It's a lot harder to justify (and come up with the cash for) a furnace setup at $10-15K or more, which seems to be what Eric and friends are talking about spending - the payback is much longer, often long enough that people don't figure on staying in the same house long enough to get it back.

Gooserider


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## Eric Johnson (Nov 16, 2007)

Actually, you can get into a wood furnace for a lot less than a boiler. The units themselves are $2,000 to $3,000 and aside from the chimney and ductwork connection, not much to do but hook it up and start feeding it wood. Wood-fueled hydronics is a whole nuther game. And yes, $10,000 is not an unreasonable estimate when all's said and done. Still cheaper than most cheap cars, and it starts paying you back immediately, instead of constantly draining your bank account.


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## pistonslap (Nov 16, 2007)

This is my third year of having a wood furnace. I wasn't real happy with it until recently when I hooked it up to the cold air supply side of my gas furnace. I could never get the heat circulation I wanted. Now with my gas furnace fan ciculating the wood heat, my house is very comfortable. My only problem is that I am running my gas furnace fan constantly. I need to find a way to run my furnace blower in sync with my woodburner blower. Are there any products that accomplish this? If not, any ideas of how to do it?


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## Eric Johnson (Nov 16, 2007)

It's not my area of expertise, but I suspect you can run a wire from whatever is controlling the blower on your wood furnace to turn on the gas furnace blower at the same time. If the voltage is different you might need a transformer or a relay, but I bet they're both 120V. Should be easy.


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## pistonslap (Nov 16, 2007)

I was thinking something on the order of an A- B switch so that I would still be able to run the gas furnace when necessary. My gas furnace is 4 yrs. old and has a circuit board that everything is wired into.  Nobody will ever accuse me of being an electrician so I may have to talk to my furnace guy $$$


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## Eric Johnson (Nov 16, 2007)

Keyman is an electrician and guys like elk and nofossil know a lot about wiring. I'd give it a few days before spending any money, although in the final analysis, that might be your best bet.


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## Nofossil (Nov 16, 2007)

Safest way is probably a relay. They're pretty cheap and relatively easy to wrap your head around. Don't know about code implications, though. I can sketch out a circuit if that's the way you end up wanting to go.


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## Gooserider (Nov 16, 2007)

Eric Johnson said:
			
		

> Actually, you can get into a wood furnace for a lot less than a boiler. The units themselves are $2,000 to $3,000 and aside from the chimney and ductwork connection, not much to do but hook it up and start feeding it wood. Wood-fueled hydronics is a whole nuther game. And yes, $10,000 is not an unreasonable estimate when all's said and done. Still cheaper than most cheap cars, and it starts paying you back immediately, instead of constantly draining your bank account.



OK, I hadn't been making a big difference between "furnaces" and "boilers" - you are right the HVAC type units are a lot less than the boilers.  I also agree that the boiler option is less than most new cars, but it's still a lot longer payback.  Given the numbers I've seen for average time people stay in a house, it seems that one could question whether a hydronic system would pay back soon enough.  I'm also not convinced that a wood system would pay back for home sales - As part of "possibility planning" when Mary-Anne got her layoff notice, we called a couple real estate places to find out what the house might be worth if she needed to relocate and sell it.  One guy's first reaction as soon as he walked in was to say that the two woodsheds w/ 7.5 cords in them, plus the additional 2-3 overflow cords stacked next to them was a NEGATIVE...



			
				pistonslap said:
			
		

> This is my third year of having a wood furnace. I wasn’t real happy with it until recently when I hooked it up to the cold air supply side of my gas furnace. I could never get the heat circulation I wanted. Now with my gas furnace fan ciculating the wood heat, my house is very comfortable. My only problem is that I am running my gas furnace fan constantly. I need to find a way to run my furnace blower in sync with my woodburner blower. Are there any products that accomplish this? If not, any ideas of how to do it?



I suspect you would need to do a home brew setup, but it shouldn't be that hard.  The only big concern I would have is that you would want to be sure that feeding power back along the gas blowers lines when the gas furnace thinks it's off won't hurt anything in the gas furnace electronics.  Unlikely, but possible.

To avoid this, I would come up with an independent power supply line for the blower, and put two relays in parallel to control it.  One relay would be switched by the gas furnace, the other by the wood furnace - if either or both are on the blower works, if both are off the blower doesn't.  Since the only thing that either unit would "see" is it's respective relay coil, you have total isolation and safety for the control circuitry.  (This assumes there isn't any sort of safety circuit that checks to see if the blower is on, if there is, you'd also need to figure out a way to satisfy it....)  

I don't like the idea of a manual switch, as my idea of having the dino-burner is to have an automatic safety backup - If something happens to keep everyone out of your house for a week unexpectedly, the dino heat should kick in automatically at least enough to keep things from freezing - a switch that has to be thrown defeats that.

Gooserider


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## pistonslap (Nov 18, 2007)

Thanks for the suggestions. I'm going to talk to my boss today, he installs gas furnaces and air conditioners as side work. We haven't had any really cold weather yet, but based on how it's performed with the gas blower in 30's and 40's, it's a big improvement.


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## Nofossil (Nov 18, 2007)

I'd do a DPDT relay - it's like two three-way switches ganged together. I'd set it up so that the gas blower was connected to the 'common' terminals.

The 'normally closed' contacts would go to the gas controller, so that when the relay is unpowered, everything works as it does now.

The 'normally open' contacts would go to 120vac line (assuming it's a 120vac motor), so that when the relay is energized, the fan is on. 

I'd connect the relay coil in parallel with the wood blower motor, so that when the wood blower is on, the relay is energized.

That way, the gas blower operates exactly as it does now, with no electrical difference, when the wood blower is off. When the wood blower is on, the gas blower operates, but is electrically isolated from the gas controller - no possibility of electrical back-feeding to the gas controller.

I'd make a wiring diagram, but I need another cup of coffee first.

Thoughts, anyone?


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## derbygreg (Nov 19, 2007)

johnsopi,

What kind of furnace do you have?

how about a link or picture?

I agree with what you say in your profile.


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## eernest4 (Nov 19, 2007)

I think nofossel hit the center of the bullseye, sounds like just the way I would do it.
1968 associates degree electronics,ct school of electronics.


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## johnsopi (Nov 19, 2007)

Mine is a Yukon big jack.  http://www.yukon-eagle.com.
 As far as tieng into the central air goes look at page 6 http://www.yukon-eagle.com/Portals/0/bigjack.pdf This can explains much better then me,and because it is a pdf file I can't cut and paste.


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## Tony H (Nov 19, 2007)

nofossil said:
			
		

> I'd do a DPDT relay - it's like two three-way switches ganged together. I'd set it up so that the gas blower was connected to the 'common' terminals.
> 
> The 'normally closed' contacts would go to the gas controller, so that when the relay is unpowered, everything works as it does now.
> 
> ...



Sounds like it would work well. One other thought if it's a newer furnace it might have a relay installed for seperate blower operation if so you could wire another thermostat directly to this and set it the same as the wood burners or use one of those dual fuel  thermos to run the blower and wood burner


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## reaperman (Nov 20, 2007)

I currently have a wood furnace in my new home which was installed during construction. I really wanted a woodstove, but I knew the best way of heating the entire home and basement was with a wood furnace. I knew I would miss the radiant heat from a woodstove. But I figured I'd take advantage of the newly installed ductwork. It worked just great last winter, my first burning year with a wood furnace. The HVAC guy who did the install, never hooked the wood furnace to the return air vent. It didnt seem to make a difference in heating, but I wanted a 2nd opinion. So my wife's, cousin, who does HVAC, was visiting a few months ago. I had him take a look at my set-up. I asked if he would duct in the return air to the wood furnace. He said I didnt need to, yet. My basement isnt finished-off. The mechanical room is studded but no sheeting on the walls. There is a open stair-well, close to the mechanical room, which was all I needed to get return air, he figured. If I sheet-in the mechanical room, blocking off the stairway, then I would need to duct in return air, but not until. I asked him about running the furnace fan at the same time for return air. He said it could be done with a relay easily enough. And I think he said another relay could be installed to drop the speed of the circulating fan. A low fan setting is all that's needed to circulate air. But he again figured I didnt need this either.   I was surprised a new gas furnace didnt have variable fan settings.  But I guess who monkey's around with that kind of stuff.  I'd check into  slowing down your furnace fan if possible, I think that would get annoying running constantly with the fan on your wood furnace.  Best of luck.


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## stoveguy2esw (Nov 20, 2007)

one thing to bear in mind ,most furnaces (wood add ons) have a "capacitor assisted" blower mounted. this type of blower does not like to be slowed down , the capacitor tries to make up the shortage of power usually with bad results. now the "whole house" furnace is likely not using one of these, so it can be slowed, but take care to check before trying to do that with the blower on the add on wood unit


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## Gooserider (Nov 20, 2007)

reaperman said:
			
		

> I currently have a wood furnace in my new home which was installed during construction. I really wanted a woodstove, but I knew the best way of heating the entire home and basement was with a wood furnace. I knew I would miss the radiant heat from a woodstove. But I figured I'd take advantage of the newly installed ductwork. It worked just great last winter, my first burning year with a wood furnace. The HVAC guy who did the install, never hooked the wood furnace to the return air vent. It didnt seem to make a difference in heating, but I wanted a 2nd opinion. So my wife's, cousin, who does HVAC, was visiting a few months ago. I had him take a look at my set-up. I asked if he would duct in the return air to the wood furnace. He said I didnt need to, yet. My basement isnt finished-off. The mechanical room is studded but no sheeting on the walls. There is a open stair-well, close to the mechanical room, which was all I needed to get return air, he figured. If I sheet-in the mechanical room, blocking off the stairway, then I would need to duct in return air, but not until. I asked him about running the furnace fan at the same time for return air. He said it could be done with a relay easily enough. And I think he said another relay could be installed to drop the speed of the circulating fan. A low fan setting is all that's needed to circulate air. But he again figured I didnt need this either.   I was surprised a new gas furnace didnt have variable fan settings.  But I guess who monkey's around with that kind of stuff.  I'd check into  slowing down your furnace fan if possible, I think that would get annoying running constantly with the fan on your wood furnace.  Best of luck.



Another thing to bear in mind if you start closing in the mechanical room is to think about where the wood furnace (and the gas unit for that matter) will be getting their combustion air from.  You might need to add outside air to them.

Gooserider


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## johnsopi (Nov 20, 2007)

My wood furnace is tied into the cold air return. That is were also were the fan is. So the fan pulls from the cold air return. It is just like a oil furnace as far as the setup go. Whats real nice is in the summer I use both furnace fans to blow the cold air to the 2nd floor.


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## laynes69 (Nov 20, 2007)

Thats the problem with the wood furnaces. They are installed right beside the main furnace. I have mine installed in series, 2 wires from my wood furnace to my LP Furnaces board, thats it. Now the thing is to NOT have any returns in the basement, or the room if you are using a furnace. The problem with most of them is they have independent blowers, which draw air from the room with the main furnace. When I reducted mine, I took out all air returns in the basement. I also have filtered outside air by the wood furnace, just incase it needs it. I know I can close my basement up, and not lose any combustion air, or have negative pressure in my basement. They do work well when using the main cold air returns in the house. One other option for your wood furnace, would be to put a limit in the plenum of the main furnace. If the air gets to a certain temp, then the Main furnaces fan could kick in for assistance. This way it doesn't run all of the time, only when certain temps are reached.


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## johnsopi (Nov 20, 2007)

I added air ducts in my basement, so I could control the house temp a bit more. It would get to hot some times.  My furnace is set up as a stand alone unit.


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## pistonslap (Nov 24, 2007)

Thanks for all the suggestions guys. My boss looked it over and said the relay is the way to do it. He's coming over Monday to set it up. I wonder how much warmer the house will be when the blower is not blowing cold air between woodburner blower cycles. As it is, the house is so much warmer than last winter and a much smaller fire is doing the job. I think I might start saving for a new wood furnace instead of a fireplace insert.


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## synthnut (Nov 24, 2007)

I have a fan/limit switch with a probe that goes into the plenum on my wood burning furnace .....What happens is that I start a fire in my wood burning furnace where the ductwork  is tied into my oil fired furnace .....When the temps get up to where I have them set on my fan limit switch, it's wired to the fan on my oil furnace, and the fan kicks on .....The air is pulled from the plenum of the wood furnace ,  and it cools down and the fan shuts off ....It cycles like this about 3 times while the fire is building , and then the fan stays on and blows warm air thru all the duct work ....I also have a hand  regulated duct in the basement that I can open or close ...I leave it cracked open so that the basement get's warmed while the upstairs also get's warmed ....There is an thermostat for the oil furnace , and also a thermostat for the wood furnace ...I turn the oil thermostat all the way down , and the wood thermostat up to the temp I want ...Its not very accurate , but it sure gets  nice and warm in the cabin ...If I let the wood die down , the air in the plenum gets cold, and shuts the fan off ....I have my oil thermostat  set to 60 degrees so that if fire goes out in the wood furnace, and shuts down , and the room cools all the way down to 60 degrees , the oil furnace will fire ....  This never happens as I feed the wood furnace till the house gets up to 75-80 degrees and it takes a while for it to drop down to anything under 65 ..... I put enough wood in it that it will run until about 12 midnight , and then let it slowly drop from there ...If it's 25-30 degrees outside , by the time it's 6-7am the house is still at about 65 degrees or so ...When it gets colder out, I can add more wood for the fire to continue longer .....Jim


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## Gooserider (Nov 27, 2007)

johnsopi said:
			
		

> My wood furnace is tied into the cold air return. That is were also were the fan is. So the fan pulls from the cold air return. It is just like a oil furnace as far as the setup go. Whats real nice is in the summer I use both furnace fans to blow the cold air to the 2nd floor.



Not quite what I was talking about - I hope...  

There are two air supplies that one needs to worry about w/ forced air heating.  One is the air that gets circulated around the house after being heated.  I think this is the air supply you are thinking of John.  It can come from the general basement, but then one needs to make sure there is adequate air return from the rest of the house to the basement, and possibly about any excess radon in the basement.

The second supply is the air that feeds the fire, and which should be getting sent out the chimney along with all the noxious smoke.  In many setups this is just air coming from the general basement area, which isn't a problem in and of itself, but which CAN be an issue if there are not enough sources of "makeup air" to replace what the fire consumes.  This is especially the case if there are two or more air consuming appliances in the same area, as if the makeup air supply is not adequate, one appliance can reverse the flue of another in an effort to pull it's makeup air in through the chimney - this sort of works, but also can introduce carbon monoxide and other fumes into the house.

Solution is to supply outside air to one or more of the appliances so that you reduce the demand for makeup air.

Gooserider


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## RCBS (Nov 11, 2008)

we use a temp. controlled relay switch in the cold air return of our HVAC.  when temp get high enough in the cold air return, the squirrel cage kicks on.  no blower on the furnace itself...gravity induction to CAR.  besides that, your funace fan shouldn't be drawing much amperage, and you can never have enough circulation IMO.


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