My homemade outdoor wood furnace (boiler)

[lapeer20m]

I spent over $3,000 on propane last year during the first winter at our new home. OUCH!

My goal is to reduce my propane use by at least 50%. I live on almost 60 acres and have a nearly limitless supply of "free" firewood.

The house is multi-story non open floor plan and is poorly suited to heat with a single indoor wood heat source. I also already have boiler heat, and the wife doesn't like the mess of having a wood burner in the house.

There are several downsides to an outdoor boiler, but i think in my particular case the positives outweigh the negatives.

I am a bit of a hillbilly, and often take a "safety third" approach to things.

I spent the summer looking for a source for used propane tanks to no avail. About a week ago, i found this for sale along side the road: It is a giant wood stove made from a 500 or 1000 gallon propane tank.

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I also have laying around, a 119 gallon welltrol well tank with a bladder inside. I picked a pair of them up at auction a while ago for $20 a piece. They have a diameter of about 26 inches, and a circumference of approximately 81 inches.

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I got to work carefully measuring and marking the blue tank, then i cut the end off with a circular (skillsaw) saw equipped with an abrasive blade. I bought this saw at a garage sale for $5.00

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This blue tank is about 1/8" thick. I think it was rated for 125 or 150 psi. I would prefer a thicker tank, but tanks are relatively difficult to source.

 

[lapeer20m]

Then the real challenge:

cutting the propane tank. It is 3/8" thick. I don't have a plasma cutter. I thought that cutting it with a torch or arc welder would be too messy as i want to weld the pieces back together when i'm finished.

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it took a little less than 4 hours of saw time to complete this one single cut around the circumference of the tank. The ID of this tank is about 31 inches, with a circumference of almost 100 inches. That's more than 8 feet around! Surprisingly, the motor on the $5.00 garage sale saw never got too hot to hold onto.

Next, I traced a line around the inside of the cut off piece of propane tank....

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[lapeer20m]

Fortunately, the opening for the door, as well as the draft control all fit within the confines of the blue tank. Next i welded the blue tank in place.

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Then i slid the blue tank inside the propane tank....

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[lapeer20m]

then i turned the entire contraption on it's end so gravity would help hold the top in place. Then i welded it back together.

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They are certainly not going to hire me to weld submarines together anytime soon. Now is probably a good time to point out that i've had exactly zero hours of formal instruction when it comes to welding. I had just a couple of small leaks during the first test. Just a little grinding and rewelding in a few spots and she is good to go!

oh yeah, before i welded the blue tank inside, i cut out the hole for the chimney "pipe" I didn't have any 8" steel pipe laying around, and i'm too cheap to run out and purchase some. I do however have a bunch of free fire extinguishers. So i picked out a couple of CO2 units with about a 10" OD. I still need to cut the ends off and weld them together to make the required length. CO2 Fire extinguishers are rated for more than 1,000 psi. They are thick, high pressure tanks. Should make a perfect chimney.

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I cut this hole using a jigsaw and a bosch blade, plus near constant lubrication. I think this tank is twice the wall thickness that the blade is rated to cut. I would have completed the entire circle with only one blade, except it bound and snapped. So it ended up requiring two. It took the better part of an hour to complete this cut. I probably could have done it in a minute or two with a plasma cutter.

 

[lapeer20m]

So far i've used 10 pounds of mostly 6013 welding rod.

I still need to weld the chimney in place, as well as a few pipe fittings. I figure that one more day of labor and I will be finished welding.

Then i plan to wrap the tank with fiberglass batting before building an enclosure around the boiler. This large enclosure will be filled with special insulation i picked up for free. There is a factory near here that utilized blue dow foamboard with an R rating of 5.0 per inch. They use CNC machines to shape this material for their application. They are left with small blue foam pellets as scrap material which they give away for free to anyone who wants it. I picked up a large quantity of this material. I then plan to build a shed around the boiler.

The 1" pex lines will run through an above ground wooden tunnel that is 18" square, filled with the same insulation that is more or less rated at R 5.0 per inch. The booiler will be about 25 feet from the house, and due to topography, several feet higher than the boiler room inside the house. The lines should have an R value of at least R-45. Much better insulated than even the most expensive insulated PEX. Not everyone can run their lines above ground, but in my application it should work out beautifully. That side of the house is a steep hill that is not easily traversed and it is almost completely hidden from view. With the backhoe i plan to make a nice not-so-steep walking path from the house to the boiler making it easier to fill the beast during the winter months.

 

[lapeer20m]

I'll post my progress as i have time.....

 

[H-Ranch]

Looks like you're going to have a low budget OWB build! I'm all about recycling or repurposing something to fit my needs. I thought I built mine relatively cheap at $2400 all in. Mine was a bit of an experiment/learning experience but I'm quite happy with how it works. I cut my propane bill for heating by 100% and I'm guessing you will also once you start running your OWB.

 

[cantoo]

Any chance you are interested in running for Mayor? Detroit could use someone like you. Good job, we think alike.

 

[avarageerod]

Looks good. The ultimate form of recycling (I'm not into recycling as much as I'm into free). I'm currently building a owb as well. It is a time consuming project. I know this because my wife keeps telling me so. Keep up the good work and keep the pictures coming.

 

[Fifelaker]

Oxygen/acetylene will cut every bit as clean as a plasma.

 

[flashhole]

Great work, please keep us up to date on the progress. Good to see innovation is alive and well in MI.

 

[lapeer20m]

I guess I should have used the torches!

I'm hoping to do the entire project for about $1k. I like free, but some things cost money up front but equate to savings over time: plate heat exchanger, pex, fittings, valves, aquastats, gauges, etc.

here is a photo of the impressive free insulation i picked up....according to an employee, this pile represents about 1 week worth of scrap.

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[u122601]

Awesome

I guess I should have used the torches!

I'm hoping to do the entire project for about $1k. I like free, but some things cost money up front but equate to savings over time: plate heat exchanger, pex, fittings, valves, aquastats, gauges, etc.

here is a photo of the impressive free insulation i picked up....according to an employee, this pile represents about 1 week worth of scrap.

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That is the coolest ideas that I have seen yet using fire extinquishers. Haha ,awesome

 

[stihly dan]

That insulation thru a wood chipper would be great in an attic. Or anything else that could grind it into pieces, especially M&M size.

 

[Patrick62]

great work there!

Your welding is okay in my book. 6013 is great rod to work with. The purist pipe fitters would tell ya to use 6011 (harder to run). You should try 7014 someday... you doing okay tho... :msp_thumbup:

Great idea on recycling all the available scrap. american ingenuity at it's finest!

 

[TheOldBiker]

Ingenious

Hats off to your ingenuity.
Two concerns;
- will the relatively thin wall expansion tank burn out in a couple of years, or are you lining it with fire brick?
- I hope you are incorporating some sort of automatic pressure relief for the water jacket

Looking forward to future installments on this project.

 

[lapeer20m]

That insulation thru a wood chipper would be great in an attic. Or anything else that could grind it into pieces, especially M&M size.

The factory already ground the insulation into "sawdust" in several of the large bags. Negative things I've read about using this in an attic: it is flammable, if it acquires moisture it does not dry out easily (unlike cellulose,) it's static charged making it messy to install and messy if you ever need access to the attic and there is no data about the r value of this material when it is ground up in small pieces.

 

[flashhole]

So if you were going to use an old Propane tank how do you keep the tank from exploding when cutting it open (torch or blade)? It seems to me that even if you open the valve for a long time there will still be some residual gas in the tank.

 

[lapeer20m]

Hats off to your ingenuity.
Two concerns;
- will the relatively thin wall expansion tank burn out in a couple of years, or are you lining it with fire brick?
- I hope you are incorporating some sort of automatic pressure relief for the water jacket

Looking forward to future installments on this project.

This will be a non-pressure boiler like most of the commercial owb. It will be vented to the atmosphere via a ball that sits on top of a pipe. The ball keeps the water from evaporating yet allows any pressure to escape.

The 1/8" wall on the firebox is a concern. However compared to a standard 55 gallon drum, this tank is much more stout. A drum will last at least a few years as a wood stove. The wall on a drum is very thin and is rated for non-pressure applications. My firebox is 1/8" thick, and was rated for 150psi. Will being surrounded by water increase or decrease the life of the firebox? I don't know.

Firebrick is a great idea, but I don't know how to line the top. Any suggestions?

 

[lapeer20m]

So if you were going to use an old Propane tank how do you keep the tank from exploding? It seems to me that even if you open the valve for a long time there will still be some residual gas in the tank.

I read about a guy who hired the kid at the scrap yard to do it. He hid behind something solid while reaching the tank with a long cutting torch. If doing it yourself you should probably fill it with water, then drain it. For added safety, after draining the water, you could connect a hose from your lawn mower exhaust running into the tank to displace standard air with low oxygen air. Propane has a realatively narrow flammable limit ~2%-10%. Too low concentration or too high and propane will not ignite.