My homemade outdoor wood furnace (boiler)

[Lapeer20m]

Last year was the first winter in our new home. It has an lpg indoor boiler and baseboard heat. We spent over $3,000 in propane. OUCH

I searched for several months for a 500 or 1000 gallon propane tank that i could use to make an outdoor boiler.

Finally, i found this: It's a giant woodstove that is made from a propane tank. It's 3/8" thick!

In august i began building the outdoor wood furnace.

I had a 119 gallon welltrol bladder tank for a well that i picked up at auction for $20. This would serve as my firebox. It's approximately 4 feet long and 26" in diameter. I'll refer to it as "the blue tank" It is about 1/8" thickness and was rated for 150psi.

The propane tank, is about 4 inches longer and 5 inches larger in diameter than the blue tank.

 

[Lapeer20m]

I began by cutting the ends off both tanks. The blue tank was relatively painless. I used a circular saw that i picked up at a garage sale for $5.00 and an abrasive blade. You can see the rust colored bladder inside.

Then i began cutting the propane tank utilizing the same method....except this tank is 3 times the thickness, and it's over 8 feet in diameter. It took over 4 hours of saw time to complete this cut. In retrospect, i should have just cut it with the ox-acetylen torches, but i was afraid it would be too jagged and difficult to weld back together.

I did finally get through it......3 days after i started. And my saw never got so hot that i couldn't hold onto it.

Here is one tank inside the other:

 

[Lapeer20m]

I was pretty happy that not only would the door fit within the footprint of the blue tank, but so would the draft control.

I should probably mention at some point that i have almost no proper metal working tools or a shop. I did the entire project outside in the driveway. Oh yeah, I also have pretty much no welding skills.

 

[Lapeer20m]

Next, I welded the blue tank onto the piece i cut off of the propane tank.

 

[Lapeer20m]

I didn't have any 8" steel pipe laying around, but i do have a bunch of fire extinguishers i picked up at an auction for almost free a while ago. CO2 extinguishers are rated for 1,200 psi and are thick walled.

I used a saber saw and 2 blades plus one can of spray lube to cut the hole in the blue tank.

Nice tight tolerance.

 

[Lapeer20m]

Then i slid the blue tank inside the propane tank.

I also welded a foot onto the back of the blue tank before inserting it into the hole.

and i welded the propane tank back together.

they are definitely not going to hire me to work on submarines any time soon. There were a few leaks, but a couple hours of grinding and re-welding and the outside eventually had zero leaks. I've done lots of cobbling things together in my lifetime, but this is the first application that has required me to weld water tight. This is a different type of skill compared to just sticking two pieces of metal together.

 

[Lapeer20m]

The co2 extinguisher wasn't quite long enough, so i welded a second tank to increase it's length. This welding is a lot easier than anything involving the blue tank. The blue tank is relatively thin walled compared to the rest of the project.

from the inside....

 

[Lapeer20m]

Welding the chimney on the inside was not a lot of fun. I used a fan to pressurize the tank and blow the welding fumes out the chimney while i was welding. I also wore a respirator, just for fun. I had to crawl inside to do the welding. Plus, upside down i weld even worse than horizontal, so i was important to flip the boiler over a couple times. Also, it's really difficult to swap out welding rod while in such a small space. I did most of the welding with an older than me lincoln ac arc welder, mostly with 6013 rod. I did use a little bit of 6011, and some 7018. The 6011 seems to do a much better job while welding vertical.
I don't know how i would do this project without a backhoe. The boiler weighs several hundred, or even a thousand pounds, and it seemed I was constantly rotating it this way or that.

I did a little art work on the door....

Here is the chimney sticking out the top.

Then i fabricated a "collar" to bridge the gap between chimney and tank. This is made from the end i cut off the blue tank.

the outer ring didn't need to be so precise, so i turned up the heat and used welding rod to cut the outer diameter. It fit quite nice! It was a little challenging, because the chimney was not centered in the hole.

 

[Lapeer20m]

I test fired it for the first time.

It is pretty sweet! I cut my firewood at 24". I can put them in the firebox sideways. That's a lot of wood!

I started a fire of dry white pine, then i began filling it with water. Rough estimate, it probably holds a little over 100 gallons. There was a pretty good fire in there by the time the garden hose filled it up. Keep in mind, the boiler is not connected to any circulating pump at this time.

The starting temperature was 70 degrees

10 minutes later it was 78 degrees

20 minutes: 93

30 minutes: 115

50 minutes: 150 degrees

closed damper

64 minutes : 148 degrees

Then i had to go leave for 14 hours. I left the damper closed 100 percent.

When i returned home, the water was still 104 degrees.

The plan is to run my pex tubing above ground, inside this 18 inch diameter plastic culvert.

it's big enough i can crawl inside:

I did a lot of reading, and i decided that running pex in the ground is expensive and perhaps not the best method for my application.

I found for free, a crazy amount of dow foamboard that has been machined into small pieces. In it's original shape, this material has an R value of 5.0 per inch. With my pex lines near the core, that should give me about an R-40 for my pex lines.

 

[hobbyheater]

Welcome to "Hearth" ! A very impressive piece of "ART WORK ". Please keep up the posts as you have a very interesting project !

 

[Lapeer20m]

It is a non-pressurized system, much like most commercial outdoor boilers. It has a vent pipe with a cap on it to keep the water from boiling out, but if any pressure is created it will simply vent to the atmosphere.

I opted to run pairs of 3/4" lines rather than 1" pex simply because i already own the tool to crimp 3/4" fittings. I didn't want to spend the extra $100 on a tool i only plan to use once. Research suggests that a pair of 3/4" pipes will flow more gallons per minute than a 1" pipe.

I'll have to take more photos of the progress. I welded on fittings for a temperature gauge, an inlet, outlet, and an air vent. The design of the boiler would trap a lot of air inside if i didn't have the vent.

I hope to have the boiler installed an operational tomorrow. It'll take a while longer for me to finish insulating the boiler and complete the finish work, including adding firebrick on the bottom and a baffle for the exhaust inside the firebox.I also want to install an automated damper. I have a draft fan i could use, but i am not sure it is necessary.

 

[Lapeer20m]

My goal was to do the entire project for $1,000. So far i've spent about $1,200, but it's ok as i want to do it right, and i plan to make back 100% of the money in savings this winter.

I live on 60 acres and have more firewood laying on the ground rotting than i can process into firewood. A lot of pine and cedar, but also some hardwoods like elm and ash.

 

[hobbyheater]

Can't tell in the picture , are you using a 3" layer of sand or so on the bottom of the firebox ? The layer of sand will allow the fire to attain higher burn temperatures !
Again what a GREAT project , WELL done !

 

[Lapeer20m]

Can't tell in the picture , are you using a 3" layer of sand or so on the bottom of the firebox ? The layer of sand will allow the fire to attain higher burn temperatures !
Again what a GREAT project , WELL done !

I had planned to use firebrick, but that costs money. Sand is a fantastic idea! It's free! thanks for the suggestion. I actually wanted it because it seemed likely that firebrick (now sand) on the bottom will help to increase the lifespan of the burn chamber.

fyi, i would estimate at this point that i have at least 100 hours of welding into the project.

 

[hobbyheater]

(now sand) on the bottom will help to increase the lifespan of the burn chamber.
.

With a water lined firebox I believe sand will work better than the firebrick . The firebrick has the potential to trap moisture between itself and the steel shell of the water jacket ! Once the sand is dry I think it would wick the moisture away from the steel walls . Somebody more educated than me will tell you if I'm wrong !

 

[hobbyheater]

The draft control on our first boiler late 70s.
The draft butterfly was controlled by a low voltage ( 24 volt) type zone valve control box. Simple construction but it did the job well.

 

[WmFritz]

Nice project. That will be a good feeling this winter saving all that propane money. Good for you on your low-budget build.

 

[Tennman]

Wow!! big congrats on your skills and resourcefulness. Man... I'm having MacGyver flashbacks! I just gotta admire your innovation. We'll be interested to hear how efficient she is.... but man... you built the whole stinkin' thing from stuff you found laying around. You may not have the fanciest system here, but geeez it's gotta be one of the least expensive. My hat's off to ya! Also pretty handy to have a backhoe laying around to pick up all that heavy stuff. Anyway just wanted to cheer from the bleachers.

 

[OT_Ducati]

Looking forward to updates on this..
Nice work.

 

[rowerwet]

is it going to be inside, if not you will loose a ton oh heat without insullation. cool build

 

[Lapeer20m]

is it going to be inside, if not you will loose a ton oh heat without insullation. cool build

While an indoor boiler would be most efficient, I have neither the space or the desire to deal with the mess of firewood inside the house.

It will be super insulated when finished, and it is going to be inside of a shed. The shed should have storage for about a face cord of firewood. I won't have to stand in the snow to load the boiler and my firewood will be nice and warm. I believe that you waste energy throwing frozen wood into the firebox.

As far as costs: I did spend $475 for the propane tank delivered to my house. But it did come with enough left over to build a second boiler. I spent another $400 on o2 barrier pex, heat exchanger, and fancy 2 stage thermostat. $75 for the plastic culvert, I also have massive quantities of welding rod into the project. All the small plumbing and insulation materials add up, and I bought a new Milwaukee grinder, and the non-contact thermometer etc etc.

 

[georgia hillbilly]

Good score on the free foam!

 

[Lapeer20m]

I can't upload any photos for a few more days, but I made serious progress.

Ran all the plumbing, made all the connections, installed the heat exchanger, set the boiler in its final resting place. I was disappointed when I finished last night that the house was already 69 degrees, too warm to test the owb.

I woke up before sunrise today and started a big fire. Water temp is up to about 100 degrees now. As soon as it hits 120 ill begin heating the house.

Still a few items left to finish, including electrical, logic, and insulation.

Temps tonight are predicted in the upper 30's.

 

[harttj]

Looks good. I would run higher water temps. Below 140 the flue gases condense and causes corrosion.

 

[Lapeer20m]

Looks good. I would run higher water temps. Below 140 the flue gases condense and causes corrosion.

I let her run until she was just below 200 degrees, then I shut the manual damper. My heating/cooling buddy said that 120 degree water is the minimum that'll heat the house.

I have yet to install the automatic damper because I am waiting for the aquastat to come in the mail. I would prefer to not add a draft fan as long as I can make enough heat without it. However, I have two different fans laying around that I could use.

I'm really excited that it works as well as it does. I'm also impressed with the heat exchanger. I'm seeing about 30 degree f temperature difference between input/output for the owb side and the house radiator side.