So I built an Outdoor Wood Burner

[Jake Wise]

I have wanted an outdoor wood stove for several years now, but price has prevented me from committing. While lamenting this fact to a coworker one day he said "why don't you just build your own?" I was intrigued when he told me it was not that hard and that he had built one of his own, and sold when he said he only spent around $2200.

With that I began to assemble materials. Luckily for me I had access to two tanks already, so that major expense was down. I started with a 250 gallon anhydrous ammonia tank that would be my burn chamber and a 500 gallon propane tank that would be my water jacket. I started by filling the propane tank full of water to flush out any residual gas and then cut the end out of it at the weld. I did the same thing with the anhydrous tank. I laid the two ends on top of each other and used the smaller as a guide to cut hole for my firebox to poke through. I then put the firebox end aside to use as a door later.



After that I prepared the smaller tank to go in the larger by welding feet onto the it so it would stay level. In the pic below I am checking fit.





I also welded ports closed and made sure everything was air tight. I welded the ring of the larger tank on the smaller one. I then slid them together and welded everything. This is the part that took the longest. I plugged all the ports but one and attached an air hos to that one. I pressurized it and sprayed soapy water over everything to check for leaks. Then I let the air out welded the suspect areas and did it all over again. It felt like it took forever. Here is a pick of it hoisted up as I am looking for leaks.



After the two tanks were together I welded in the ports I would need in the water jacket. A fill port, suction port, return port, and a port for the aquastat.



My next problem was figuring out how to seal the door. My first plan didn't work out though. I put metal strapping on the the inside of the firebox and fire gasket sandwiched between.





It seemed like a good idea but ended up being too close together to get the door in so I had to cut the outside strapping off. To get the rope gasket to stay on I tied it in a circle and slipped it around the inner strapping. To be sure I got a good seal against the gasket I bent some 1/2 inch round stock in to a circle and welded it to my door. Here is a pic of my dad heating it with a rosebud to relieve the stress.



So with the seal in place the door was ready to go on. It took us two tries to get a design that worked for the hinges. Luckily we have lots of scrap metal laying around. Using some parts from a field cultivator and an old combine we built a hinge heavy enough to support this huge door.

 

[Jake Wise]

Once I got the door on there I used shims to get it to close correctly and then slathered the hinge in good Cat high temp anti-seize. With the door shutting now I built a hinge out of an old piece of a planter and some teeth from a harrow.



After seeing that other people that built these insulated their doors I took the left over piece of the propane tank cut it down a little and then welded it into my door as an air gap.



To finish out the door I added the tube to mount my blower and a cover to keep the rain off of it. You can see in this picture where I patched a hole after a mid-build design change.



The door was finished so the last major item to be tackled was the chimney. I decided to use a 7 inch fire extinguisher that I had as a chimney, so I cut a 12 by 12 hole through my water jacket and then tried to cut a smidgen over 7 inch hole in the fire box. I failed. The fire box hole was too big. We decided to break out the MiG welder because of the thinness of the fire extinguisher. This meant we had to spend 4 times as long making sure everything was clean and there were no drafts in the shop since this weld would need to be perfect. We also ended up wrapping some half inch round stock around the hole to use as filler. This worked pretty good, we only had one spot that was suspect. In order to clean that spot up dad pulled out his Air-Arc and I cut the imperfections out and re-welded. I then rolled the tank over and got inside the firebox and welded it there as well.







I then welded the outer portion back on, but due to a lack of the finer points of machine work I got the hole off and it didn't fit quite right. I just added some filler and welded the gaps. Then came pressure checks and re-welds.



With all the major things done now all I had to do was a little finish work. I am eventually going to add a taller chimney that will sit next to the unit, but until then I need to add a dampener to this one. I did this by taking the end that I had cut off and welding a nut to it and then welding a bolt to a piece of metal that I inserted into two slots cut in the stack. That way I can screw it up and down to adjust draft.



The last thing I did was add a box to put the aquastat controller in.



With everything done that I could get done in the shop it was time to load it up and take it to the house. Here we are loading it on the trailer.







I will post more as I get it installed.

 

[lapeer20m]

Awesome build!

If i understood correctly and your plan is to have a manual damper my guess is that after a few days of use you will be fabricating an automatic damper.

Home Depot online sells an auto damper made for duct work for about $60.

 

[Jake Wise]

There is already an automatic dampener on the blower fan (pic below). However, I was afraid that air would come back through the chimney since it is so short and 7 inches wide. That is why I added that adjustable top, also to keep the rain out.

 

[Pelorus]

Enjoyed this!
The finished product looks very 1945 era thermonuclear!

 

[dave_dj1]

Looks good so far, I have a few questions for you though, not being critical, just taking notes for my build (someday).
Where are your in and out ports? And did you install a long tube into the water jacket to separate them?
What size place are you heating? Did you leave chimney down into firebox any distance? What insulation do you plan on using?
Keep the updates coming
dave

 

[H-Ranch]

Yeah, why not build your own? LOL Nice job - I'm a big fan of the re-use of materials. Looking forward to more details as you get it operational.

I hope you have a long shovel if the ammonia tank is as anywhere near as long as the propane tank!

 

[Jake Wise]

dave- The outlet port is near the front about two thirds of the way down. Since it is at the front it will being pulling water that is only 3 inches from the wall of the burn chamber. The return port is on the back at the top. This way I should get circulation. The house I am trying to heat is a 2400 sq-ft recent construction 2 story. The chimney doesn't go down into the burn chamber at all, and at this point I have no baffles. I do plan to install them but I need to get this thing operational and I would like to do some more research. When I burned some cardboard in it this afternoon it shot flames out the stack...so yeah I'm loosing a little heat. As far as insulation goes at first I had this great plan to build a block structure around it and fill it with sand to act as a heat-sink/insulation, however money and trouble will probably convince me to wrap it in pink insulation and build a metal shed around it.

H-Ranch- The ammonia tank is a little less than half the length of the propane tank. The propane tank is 36 inches across and the ammonia tank is 30 inches. I am estimating somewhere a little less than 300 gallons for capacity.

 

[Jake Wise]

Enjoyed this!
The finished product looks very 1945 era thermonuclear!

When I asked my wife what she thought of it she said "It looks like a bomb in our yard." And then turned and walked off. I told her she should be more impressed.

 

[Rookie1]

Nice job. Im jealous of your workshop.

 

[colson04]

There is already an automatic dampener on the blower fan (pic below). However, I was afraid that air would come back through the chimney since it is so short and 7 inches wide. That is why I added that adjustable top, also to keep the rain out.

Hey Jake, Where did you get that blower/dampner assembly?

 

[lapeer20m]

I've been runnin mine all winter without a baffle. My chimney is all the way to the top of the burn chamber (also a fire extinguisher.)

I originally planned to build a baffle but I'm not sure it's really necessary. I also planned to put sand on the bottom of the burn chamber to act like fire brick and keep some of the most intense heat off of the metal, but never got around to that either.

 

[Jake Wise]

Hey Jake, Where did you get that blower/dampner assembly?

I got almost all the components I needed from a http://www.altheatsupply.com/. They have DIY kits for OWB builds and all kinds of stuff.

 

[farmer steve]

great job Jake good on the recycling. the wife will be more impressed after she see's the next fuel bill.
and welcome to AS.

 

[Jake Wise]

We got the wood burner transported to the house and unloaded, so now it is time to start the install. The first thing I did was to install the blower and the aquastat and wire them up. Fun side story... I couldn't wait to try it out until I had filled it up with water, as a consequence I melted the wires running to my aquastat probe. Luckily, though damaged, I can repair it with little trouble.







Then the less fun part of drilling the holes through my basement wall to run the lines through. My Dad's concrete bit set has some gaps in it so I my options jumped from a half inch bit to an inch and an eighth. Since I am running 3/4 inch lines I had to go with the bigger one. To use that thing one of us held it steady while the other one used a 2 by 4 as a pry bar to push it forward. Here is a pic of the holes with my had for perspective.



Finally got the holes drilled then installed the heat exchanger in the duct work right under the furnace. I wanted to put it after the furnace but it wouldn't work out so I had to go below. I am not an HVAC guy so this install is a bit conventional. To hold the exchanger in place I used 1x4's the I had left over from other projects.

 

[Jake Wise]

Lets see, I left off last time with the holes drilled and the exchanger in, so I will start with the inside hook up. Here are the pics. You will see that I have valves to be able to manually shut off the flow to the exchanger and a pressure gauge. I used a mix of cpvc pipe and pex.











I also installed a valve so I could fill my water tank from inside the house.



Also in the top picture you can see a grey box strapped to the pipe. That is my indoor aquastat that breaks the connection from the thermostat in the house to my power hungry heat pump compressor. It kicks the heat pump off when the water temp in the pipe goes above 80 deg.



Here is a picture of my completely uninsulated pex pumping the hot water to the house. I am eventually going to bury it, after I decide how best to insulate it. I am not loosing near as much heat as I thought I would. (Google automatically added the snow when I uploaded it to Google+)



Here is a pic of the top of the wood burner. You will notice I had to add insulation.

When I first hooked this thing up I couldn't keep temps above 120 until I put this insulation on there. Another thing I had to change from my original design was the water return location and the vent location. This all resulted from the fact that I didn't put enough effort into researching what actually goes into designing a hydronic heating system. I ordered 3/4 pex because that was one of the options for the pump I bought and because of the cost savings over 1 inch. I turns out that between my 3/4" lines, the length of the run and the fittings I had a really high head pressure that resulted in very low flow, even though I had a large pump. As a consequence there the water wasn't be circulated through the tank like I thought it would so the water around the burn chamber was boiling and going right out the 2 inch vent above it. To remedy that I took the return line from the back of the tank and put it into the 2 inch fill/vent. I capped the 2 inch vent and instead put a piece of 3/4 inch cpvc in the port where the return had been. The idea being this would cause the water to naturally circulate to the back, it has cut down on water loss.



Another issue I had once I got this thing running was the fact that it was eating MASSIVE amounts of wood. I figured out this was due to the fact that my blower fan ran full blast all the time. I bought a dimmer switch instead of the correct part and it only kind of works, but slowing the fan down saved me a lot of wood and raised the heat in the tank. It will actually go over 150, but it still won't hit 180.

 

[hedge hog]

is that a bomb in your yard?

really good job and it sounded like something my wife would say so I had to laugh.

I have kicked that Idea around but torn between forced air or a boiler .