Building my second OWB

[Jake Wise]

I started by tracking down the tanks I would need to put the boiler together. I had a 250 gallon anhydrous tank that would be the fire box but I needed a larger tank to be the water jacket. I determined that the cheapest route would be to buy a 500 or 1000 gallon anhydrous tanks, so I watched the agricultural auction sites until I found one two and a half hours away for $200.





I had built another one of these for our old house a few years back so I pretty well knew how I wanted to do it. I first considered using the entire 1000 gallon tank, but I decided that so much water wouldn't be practical, so I started by cutting the big tank in half. I then cut the end off the little one and took measurements for the end plate. I went to a local fab shop and had one cut out.









Getting the plate on was harder than I expected it to be because it turned out that the smaller tank was not exactly round. I got it tacked on and then flipped it over and welded it solid. The next step is welding the chimney pipe into the fire box before inserting it into the jacket.












On my last stove the flue went straight out the top and was only in the water jacket 3", on this one I wanted to run it out the back so it would be in the water jacket over three feet. I knew that I needed something that wouldn't be prone to failure so I used an old oxygen bottle that I cut the ends off of. One of the hardest parts was figuring out how to cut the hole the right size and in the right place. I needed to cut a circular hole in a ball in the rounded end of the tank and it took some trial and error. I put the burn chamber inside the jacket and centered it. I then inserted the flue through both and tacked it to the inner chamber. I then removed the inner chamber and welded it fully before setting the water jacket over the top of inner chamber. Me not being a fabricator by trade, and this being the real world, my end plate and my outer chamber were gaped open on one side. I used my crane to hold the tank where it would put pressure on the plate and close the gap. Luckily I'm a function over form guy.

 

[Ikeholt]

Wow! That looks great. I can't wait to see it finished.

 

[H-Ranch]

Good idea - portable on wheels!

Looks like you might be able to use the axle mount as the foot when you remove the tires.

 

[Jake Wise]

Good idea - portable on wheels!

Looks like you might be able to use the axle mount as the foot when you remove the tires.

It crossed my mind to leave it on wheels and just pull it over to the house in the winter, but the under carriage is going to become a log cart.

 

[Mike Van]

Jake - My Garn has 1000 gal of water around it, nothing wrong with it - It's the smallest one they make. I do like your open air shop -

 

[Jake Wise]

Jake - My Garn has 1000 gal of water around it, nothing wrong with it - It's the smallest one they make. I do like your open air shop -

I was worried for a couple of reasons. That 1000 gallon tank was so long that I was afraid I would have to add a circulator to keep it all heated evenly. Second, I was worried that if I messed up and let it go out I would have that much more water to heat to get it back up to where I wanted it. I like the fire all the time set up. I know some guys like to heat the water and let it go out, but I don't like starting fires that much. All that said, I have half a tank left over and I may play with storage later on.

 

[cantoo]

What is your estimate on actual water storage after you subtract the inside burner chamber? I think mine holds approx. 500 gallons of water and I've been considering adding a tank or two in the basement to allow extra storage when I heat my shop.

 

[Jake Wise]

What is your estimate on actual water storage after you subtract the inside burner chamber? I think mine holds approx. 500 gallons of water and I've been considering adding a tank or two in the basement to allow extra storage when I heat my shop.

I'm going to guess somewhere around 250 or so, it's hard to say.

 

[dave_dj1]

Looks great so far. It will be interesting to see how it performs with that much stack under water. I like the ones with the stack at the rear going way down close to the bottom of the firebox.
What is the plan for outlet and inlets?

 

[Jake Wise]

Looks great so far. It will be interesting to see how it performs with that much stack under water. I like the ones with the stack at the rear going way down close to the bottom of the firebox.
What is the plan for outlet and inlets?

I made sure that I used something thick for the stack so it could withstand creosote fires, and I am going to have a clean out. My last build had the stack set down in the box more and I had to keep and extra set of clothes I put on to feed the thing because I always got covered in smoke. The idea is to recover the heat in the part of the stack that is in the water so that I won't need to try as hard to keep the hot air from getting out so fast. As far as ports go, I had my Dad machine me some 1 1/4" weld in bungs. The return dumps on the top of the fire box and the outlet is in the back about half way up. I am planning on the pump running all the time so in theory temps should be close to equal throughout the tank.

 

[cantoo]

Make sure you weld in a few extra bungs and maybe even a coil for an antifreeze only line? Mine has 4 bungs, I heat 2 houses and getting ready to hook up my shop. Would have been nice to run the shop with an anti freeze line so I could turn it off when I want to.

 

[ChoppyChoppy]

There isn't any issue with cutting, welding, etc on an old tank that had anhydrous ammonia in it?

I'd never heard of it before so I looked it up. Sounds like it's some really nasty and dangerous stuff!

"it’s loathed for being one of the nastiest treatments on the farm. Chemically, it’s the same ammonia used in cleaners around the house, minus the water (thus, it is “anhydrous”). The vapor is corrosive to human skin and aggressively seeks out water wherever it can find it, which means that anhydrous leaks can result in horrific injuries to the eyes, throat, sinuses, and lungs."


I welded some mounting tabs on a 120 gal diesel tank this past spring. Needed tabs to bolt it down on a flatbed of a newly bought truck.

Tank hadn't been used in a while and was empty.

I thought about filling it with water, but it didn't have a drain on the bottom and would have been near impossible to get all the water out.

I kept the heat low and short welds, but still the thing caught on fire.

I was in the middle of the last weld and heard a "whooshing" noise. I thought someone had pulled up behind me in a truck as first. I lifted up my shield to see who it was and I realized that the tank was on fire inside of it!

It had a fill cap that could 2 way vent, I had pulled the cap off but set it back ontop of the fill neck. Not sure if someone screwed it back on or when it caught fire it was sucked back on. I got lucky as it was still able to vent. It likely would have exploded if it had fully sealed.

Even with that cap venting the tank puffed out and it was whistling like a tea kettle as well as doing a "woof", "woof" and the tank sucking in a bit and blowing back out out, almost looked it it was breathing

My heart was pumping for sure. The truck was right near the back of the shop and the tank was already bolted down on the one side. Open the cap and stick a fire extinguisher in? Run away? Save the truck/shop/my welder/car, etc?

It ended up burning itself out after a minute or so. Got hot enough to burn the paint off part of the tank and melt the guts of the 12v fuel pump (was a junk pump anyhow though).

 

[Jake Wise]

Anhydrous is very nasty and very dangerous, but at least not flammable. I vented it before I cut it and I didn't have any problem. The last one I built was out of a propane tank and I filled it completely full of water before cutting it. I work in the Ag sector and grew up on a farm so I had been around anhydrous quite a bit before.

 

[cantoo]

Anhydrous is the 3 breath fertilizer, you only get 3 and that's it. My wife did 1000's of acres of it years ago. I've cut lots of types of tanks before, I usually hook a pipe onto the truck muffler and let it run for awhile. Galvanized hot water tanks can be interesting too.

 

[Jake Wise]

It has been awhile since I updated this, but to tell the truth I got busy at work and haven't worked on it since last December. But, with cold weather here and a bill from the propane company I am back at it.

Another reason that I stopped was because I didn't have a good idea for the door. I wanted a full size door, but wasn't sure how to seal it. On my last build the door worked pretty well but it leaked and kept me from being able to successfully idle the stove. My problem was my shaky hands. When I cut the cap off of my inner tank I didn't get the cut anywhere near uniform. I decided to overcome this by using a piece of filler metal wrapped around the lid and welded. I ended up using 1/2" rebar because it was cheap and available, though it welded like crap. I wrapped two wraps around the door and one wrap around the metal where the door seats. My plan is to high-temp silicone a piece of 1" fire rope there to seal the door. Next thing to do is build a latch. My hinges are front lower torque rods from a Rogator sprayer that I got from work. They swing like a dream.

 

[rancher2]

Jake
Good to see your back at it. Good luck on getting the build finished up. I better go fire the Garn back up and warm the water up. Sounds like the weather is going to warm up a little later in the week.