Building an outdoor wood furnace.

[kickinbull]

we have an outdoor woodfire boiler that we bought new. It's 14 years old. I would suggest doing some research on the difference between water & air. If I recall, the water is 30 times more efficient. We have a friend that had an outside forced air furnace. Wasn't too impressed. Good luck, hope it works for you.

 

[john250]

Goods question John, usually towards the end of Feb. I also ask myself why. The main reason is I'm a cheapskate I hate buying fuel of any kind. I also have an endless supply of wood on my place I need to clean up. The beauty of the outdoor burner is it is not picky as to what it will burn, green wood, leaves, pine, if it fits in the door it will burn it as long as there's a bed of coals. The other reason for this project is I like building stuff, it keeps me out of trouble. I know what you mean about saving your back though.

Good answer. You've thought it thru. I think wood heat can't be beat in forested parts of the planet.

 

[greybeard]

Goods question John, usually towards the end of Feb. I also ask myself why. The main reason is I'm a cheapskate I hate buying fuel of any kind. I also have an endless supply of wood on my place I need to clean up. The beauty of the outdoor burner is it is not picky as to what it will burn, green wood, leaves, pine, if it fits in the door it will burn it as long as there's a bed of coals. The other reason for this project is I like building stuff, it keeps me out of trouble. I know what you mean about saving your back though.

Good answer. You've thought it thru. I think wood heat can't be beat in forested parts of the planet.

Now you done gone & do'd it.
Watch it!! The huggers and greenies will be pointing out that wood heat is part of the reason some parts of the planet are no longer forested.

 

[Nesikep]

we have an old incinerator from a hospital as a shop furnace, with 4" of firebrick it takes forever to warm up but burns anything once it gets going, it's got enough heat stored in the brick to dry out a wet log... unless it gets really cold, I use about 2 12"x16" rounds of pine wood per day

your project looks pretty nice, except for that brain fart on the exhaust hole size!

 

[HDRider]

Have you started using it yet?

 

[ohiosteve]

I appreciate all the advice and questions but unfortunately my time is limited and this project has been dragging on, but I have made some progress.
After much debate I have decided to try to use an old 1000 gal. propane tank I salvaged as the outer shell for the burn chamber. My big concern is the smell which I hope I can burn out of it. I cut it it in half with a chop saw and here I am marking the top for a 20" pipe.

Then I torched the 20" hole in top.

After that I propped it up on some blocks and started a real hot fire and had it glowing red. The next morn the smell was gone.

 

[ohiosteve]

I then cut the outer jacket in half.

Then I welded the 20" connector pipe to the burn chamber.

Here is the outer jacket with some spacers in place waiting for the burn chamber to be positioned.

I am happy to be this far on this project but now I need to decide where to put my draft induction.

 

[J&D Cattle]

Looking good; man I'm jealous of your farbricating ability. I can barely strike an arc.

 

[wade]

Nice project. Might I add a couple things just for thought. I use wood to heat my home during the winter. I have a forced air wood furnace inside a separate room attached to my house. I ran my duct work off the wood furnace into my existing duct work that is also hooked to my propane furnace. I also connected into the cold air return. My wood furnace has a neat design in which the chimney is ran out the top and back of the stove. There is a sliding plate which forces the smoke and heat to go toward the front of stove and then up and then toward the back of stove before going out the chimney. When I want to open the door to fill the stove I pull a rod that pulls the smoke plate toward the front of stove and lets the smoke go straight up the chimney. The other suggestion I might make is to make a grate in the bottom of the stove where the ashes fall through and drop below the fire box. Otherwise you have to let your fire almost go out to clean out the ashes. Just a couple suggestion. If you like them great. If not that's fine also.

 

[ohiosteve]

Yep wade, I plan on running this furnace right through the existing ductwork in my house. mwj was asking how the heat will be extracted and it's hard to explain without pictures but what I am calling the plenum (the space between the burn chamber and the outer heat jacket) will be split in half horizontally. The lower half will be the cold air return from the lower level of the house and connected to a powerful squirrel cage fan that will force the hot air from the bottom of the plenum up and around the top of the plenum and into a 8" x 16" duct that supplies the entire house. This fan will be operated on a heat switch (I forget what it's called), in the plenum and will only kick on when the plenum is at a set temperature (approximately 90 degrees). Therefore when the thermostat in the house calls for heat, the draft inducer kicks on making the fire roar and then the plenum temp increases kicking on the main blower and heat is blown through the ductwork.
My explanation probably sucks but I will post some pictures as I proceed with the project.

 

[tripleBfarms]

I would try to insulate the outside of it somehow to save some heat. Looks good. Wish I could cut and weld that good.

 

[Nesikep]

I can say I don't think you'll burn it out in your lifetime, or your kids... must weight a ton

using forced air I don't think you'll run in to a problem, but if you were using water, I'd be concerned about the ability to get it hot enough to clean itself out. one of my friends has one and it creosotes up so badly the efficiency is half of what it's supposed to be... guess it depends on the wood you burn too

Looking good so far

 

[bigbull338]

to keep the creosote burned off you have to have hot fire burning.oak hackberry an red oak are hardwoods that burn real hot when they are cured out all the way.

 

[Nesikep]

yeah, the trouble is when the water coils, or whatever heat exchanger you have works too well and you can't get anything past the firebox hot enough to burn... that was my friends problem

 

[ohiosteve]

I've made a little progress even though I spent most of Saturday tailgating and watching by beloved Buckeyes beat up on Penn State. Brutal.
I decided on thick wall 2"x4" tubing for the draft induction, it runs almost half way through the burn chamber and has holes cut in the bottom.

Then I welded the horizontal dividers in.

Here is the rear where the blower will be.


Here is the blower in place, next I need to position the upper cover. I plan on insulating the outer cover and also building a small tin "doghouse" over the entire furnace. I was welding in snow the other day and that motivated me to get this project done.

 

[bigbull338]

your wood furnace is really coming togather an looking good.

 

[ohiosteve]

your wood furnace is really coming togather an looking good.

Thanks bigbull, I appreciate the compliment. I hope in 50 years or so my grandkids are using it and talking about their crazy grandpa who built the thing. Tonight I got the upper shell tack welded into place. Crappy picture but hopefully it shows how the airflow will be.

 

[john250]

I may have missed this. How will you feed this beast. I'm impressed.

 

[ohiosteve]

It's been a while since I've posted but I've made some progress.
Here's the rear view the inlet is on the bottom the outlet is on top.

Here's the pad where it will sit.

Here's the door.

 

[ohiosteve]

Here it is hooked into the house and somewhat insulated.

Here is the rear and the very important fan/limit switch which tells the fan when to kick on/off and will kill the draft inducer fan if the temp gets too hot.

Here is the start of the "doghouse" that will contain the beast. If I was more organized this project would be complete, but I must say It has been very cold this winter and my house has been like an oven.