Neighbor Has a Outdoor Wood Forced Air Furnace.

e.alleg · Post by **e.alleg** » Sun. Oct. 14, 2007 9:06 pm

My neighbor hooked up a weird contraption, it's an outdoor forced air wood furnace. It is basically a 55 gallon drum wood stove inside a much larger steel drum. The airspace has two ducts coming off it, one is a return air duct and the other one is the supply duct. The fan is inside the house. He says it works great, it definitely keeps the wood mess outside. Kind of a cool setup.

LsFarm · Post by **LsFarm** » Mon. Oct. 15, 2007 12:30 am

The ducts to and from the furnace must be short and well insulated. Air is the worst medium to use to carry heat from one place to another. Heck, an air space is considered insulation, and regular insulation materials are just enclosing lots of small air spaces to resist the transfer of heat...

That's why most outside burners use hot water to conduct heat to the house.

I'm not surprised that someone has done this. It would be interesting to find out how effecient it is or isn't. I would believe that the inner 'hot-box' may burn out quickly from the high temps created with only air to conduct the heat away.

Keep us informed. Any chance of posting a photo or two of the unit??

Greg L.

ktm rider · Post by **ktm rider** » Mon. Oct. 15, 2007 1:40 am

I think it might be like this

http://www.charmaster.com/embers.html

blue83camaro · Post by **blue83camaro** » Tue. Oct. 16, 2007 1:19 am

My dad wants to build a unit like that to heat his garage. It is a better deal for him because it will not be used every day so there is no water to worry about freezing. I think that it should last fine if built properly. Look at how long wood furnaces last indoors. I think the key to durability is protecting the metal from coals with firebrick and maintaining airflow thru the unit. I don't think I would want to use one of those to heat my house though. I would rather have the hot water there are a lot more options such as heating domestic hot water and heating out buildings.

ktm rider · Post by **ktm rider** » Tue. Oct. 16, 2007 5:20 am

blue83camaro wrote:. I think that it should last fine if built properly. .

I would'nt be so sure. I think condensation inside the air ducts would reak havoc in just a few short years.

e.alleg · Post by **e.alleg** » Tue. Oct. 16, 2007 11:14 am

no photo's, I don't know him that good and we live way out in the mountains. He might think I'm a government spy or something. It's kind of the like Charmaster but a lot cruder. Imagine a 55 gallon oil drum on it's side with a door welded on one end suspended inside a 275 gallon oil drum. I would worry that any leaks in the stack or a pinhole in the fire drum will make it so the house gets pumped full of CO, god forbid a large hole develops and it pumps hot coals into the house. We'll see how it works out, I have to applaud the guy for not just paying the Propane man.

blue83camaro · Post by **blue83camaro** » Tue. Oct. 16, 2007 8:04 pm

ktm rider wrote:
blue83camaro wrote:. I think that it should last fine if built properly. .
I would'nt be so sure. I think condensation inside the air ducts would reak havoc in just a few short years.

I doubt it would harm the ducts look at the condensation on uninsulated ducts with air conditioning in the summer. The problem will be the fire chamber getting condensation in the summer. All you have to do is make it out of thicker plate and you will buy more time. I would assume it shouldn't rust any worse on the air side than it does in the firebox. Just a thought.