Introduction: Convert a Electric Water Tank to a Outdoor Wood Heater

Picture of Convert a Electric Water Tank to a Outdoor Wood Heater

I recently developed an interest in welding and so began looking for a welding project. With winter around the corner I began scanning Instructables for outdoor wood heater inspiration. Lots of great ideas and creative approaches. Many use gas cylinders which are a perfect size but has an element of risk. By chance I came across a dumped electric hot water unit, and even though a bit on the larger size, I thought why not.

Materials & Tools
1x expired electric water heater of any size.
1x 2M length of 100mm round tubing or equivalent for the flue
Reinforcement steal rod
Steal RHS
Steal angle
Angle grinder with scourer pad and cut off discs
Multi Tool
Jig Saw
Welder (Mig)

Step 1: Heater Strip Down

Picture of Heater Strip Down

To be honest this step started out as a bit of fun but I was over it by the end. The dome top and bottom of the cylinder being the trickiest and therefore most time consuming. The body was relatively easy, just score a grid pattern around the circumference. The horizontal scores were about 30cm apart, the vertical score was the depth of my multi tool blade – about 5cm. Then basically shear the thing like a sheep. As you can see it came off pretty cleanly in rectangular blocks, created a huge mess in the shed, but cleaned up very well. Note that I actually left the bottom section on right up to Step 6, this allowed me to use a spirit level to mark out in the next step.

Step 2: Cut Out

Picture of Cut Out

The first thing here is to point out that the bottom of the tank is the top of the heater. This was not a deliberate decision but one that worked out very well when I got to the flue stage. Once clean I noticed several horizontal tooling marks on the body and decided to use these as reference. Using the spirit level I marked down a vertical reference line. Using two of the lines (approx 41cm apart) I marked out a 40cm wide door. Using two more of the tooling marks I nominated a section to remove, shortening the height of the unit. First the door and then the mid-section was cut out using an angle grinder with cut off disks (plural), and finishing the door cut with a jig saw. The inner plastic tubes and anode were then cut out.

Step 3: Fire Grill

Picture of Fire Grill

From the removed mid-section a 7.5cm ring was cut – diameter of the tank is 60cm. This ring was shortened to 125.66 cm and re-joined. This was the first weld to the inside of main tank and where I discovered that it is coated in glass. All prospective weld points required grinding down to bare metal. Closing the ring manually was a bit of a task that means the new ring is “circle-ish” in shape. New diameter is now 40cm. Two 40cm pieces of reinforcement rod were cut and used as bracing inside the ring. Using a thin piece of scrap timber as a guide each rod was marked, cut, and welded in place to complete the task. The fire grill was installed through the open top of the unit. The grill itself is too large to fit through the door area. It is very solid and easily takes my body weight so I do not see any need to be able to completely remove. The ring can be comfortable lifted through the doorway to access the bottom of the unit for things like cleaning.

Step 4: Ash Collection

Picture of Ash Collection

The original thought was easy enough – create a door of some kind to remove ash from the unit. I looked at the scrap pile and using an off cut of 9cm square tubing a solution (maybe not the solution, but a solution none the less) came together.
The ash collector uses two pieces of the tubing. The longer of the two – approx. 15cm makes the main chute. The second was cut into four sections - one retaining the corners for use as the bottom, another retaining a section of angle to use as a sliding door, and two thin sections to control the sliding bottom door.
The thin sections were clamped and welded to the main chute first. The bottom piece was next after being trimmed to allow clearance of the sliding door. A square hole was then cut into the bottom using the angle grinder, finished with the jig saw. The door slide itself has a bold welded to it for use as a small handle.

Step 5: Air Intake

Picture of Air Intake

The idea for air under the fire was to help promote a good draft and so a cleaner burn. Unfortunately I found out after that wood fires work best with air at the same level as the flame. So this was one of those learning exercises that I did this time and will change in the next.
Anyway what I did was take a 15cm x 5cm off-cut, which was 30cm in length, and cut a square hole in it for my ash collector. I then cut out a 15cm square from the bottom of the tank. To have this tube sit flush I needed to cut an arc in the front of the hole. This arc is horizontal across the curve of the bottom dome. Having access to a laser level would have make this very easy. No laser meant I simply gave it my best guess. As it turned out it was not perfect but reasonably close. Once happy with the cut I placed the tube in, used two magnets to hold it horizontal while I marked the arc on the tube from the inside. I didn't cut this arc exactly, I wanted to retain a small lip that I could weld to from the inside of the tank.
From here I welded the ash collector and a back piece to the tube and, after confirming the fit on the main unit, welded it in place. The outside weld was very straight forward, the inside weld was a bit awkward. A bit of grinding was required to expose the bare metal before I was set to continue. The depth of the unit made getting the mig hand piece close enough quite tricky. In the end though I did succeed in completing the joint.

Step 6: Top Section

Picture of Top Section

As I mentioned earlier I did not clean off the insulation from the bottom of the heater until now. When I did I discovered an access port that I was not aware of. The fortuitous part of the discovery is that with the access door removed the hole is a perfect fit for my flue tubing.
The door I put back to use as a damper. For this I welded 3 bolts to the dome, after grinding off enough glass, and simply bolted the door down. Using the bolts means the damper can be adjusted or removed any time.
Hint: The flue was not installed at this time. At about this stage in the project I started thinking about evolving this concept into something more.….

Step 7: Base

Picture of Base

Another ring was cut from the removed mid-section. To get an even cut I marked around the ring using two off-cuts of timber, ensuring that the line at least was parallel with the floor. Again the angle grinder with a cut-off disc(s) made the cut. Steel RHS was cut and joined to make a cross. The ring was placed over the top, positioned/centered, and marked for cutting. Welding this back in completed the metal work of the base.
Before continuing to the legs I used the ring to mark out a round cut on a sheet of MDF. At this point I am uncertain of whether I will use or not. My preference is to use some cement sheeting in which case I will use the MDF as a template.

Step 8: On Its Feet

Picture of On Its Feet

Four 75cm legs were cut in 5x5cm angle iron, and once squared up were welded to the base ring.
With the unit upside down I cleaned up the welding areas, positioned four wooden sections, and sat them on timber wedges around the unit. The base/legs were rested on the blocks and using the wedges adjusted until level. Once I was happy the levels I gave each leg a small tack weld and confirmed levels again. After completing the tack welds all-round, the unit was laid horizontal and the leg welds completed.

Step 9: Securing the Top

Picture of Securing the Top

The body of the tube is cylindrical but not perfectly round. The lid will sit on the top, it does closely line up, but not exactly. Plus I was also considering the evolution of this project and so was not keen to just weld it back the best I could. What I decided was to clamp the top on.
Another ring was cut from the mid-section and cut on the original joining weld. Two pieces of angle iron were prepared and tacked to the ends. To get the ring to sit in place while the top is positioned I drilled a couple of small holes and slipped in a nail. This is enough to hold the ring in the correct position while the lid was positioned and then tightened. In hindsight I should have used this method to create the fire grill.

Step 10: Test Drive

Picture of Test Drive

Take one sunset, a bucket timber, and some paper – light it up. The first test fire worked very well. There was a little bit of cross wind that seemed to draw smoke through the door but when that died back the flame/smoke was straight up. The little ash that was left was basically just a powder. The second fire was a good bit more intense. A larger fire running for several hours that at one stage started to appear through the open top of the unit. I am very happy with the heat retention and operation of the unit. The large doorway does however let out more smoke that I would prefer. I am going to lower the damper before the next test to compare.

Step 11: Final Tidy … Before Phase 2!

Picture of Final Tidy … Before Phase 2!

The body of this unit has five water input/output ports that will need to be trimmed and sealed. There are also the two element ports, one of which I have already done. Final task for this phase will be to remove the remaining paint from the exterior and cover with Pot Belly Black paint.

Step 12: Post Mortem

All in all a great project, and one I have thoroughly enjoyed. My gasless Mig welder has had a really good workout and I must say that I am much more comfortable with it now. Not that you can see my welds very closely but I describe them as functional, certainly not pretty.
About half way through the project I realized that this thing was going to be huge. Perhaps too big really for what I had originally intended. Rather that cut it down further I chose to press on. The original plan was simply to create a wood heater from an electric hot water service, which has been achieved. Now I want to evolve this into an outdoor wood pizza oven. Fix a door to the unit, work on a better air flow system, fit a shelf with fire bricks in the top section, create a second “oven” door, properly flue the top, and permanently secure the top section.
Defiantly another Instructable in the Pizza Oven conversion!


mtbike2 (author)2017-01-03

for anyone doing this now it is much easier to use a flat pry bar and simply scrape down the side using the long end to chisel the foam off. Then use a dry wall spatula to scrape anything that remains off. It's super fast that way.

SabinaCowan (author)2015-11-12

Wow, first dibs on pizza :o)

CorreyS1 (author)2015-09-17

Oh wow, that's pretty cool that you can create a water tanker into a wood heater. It would seem like a good idea to do something like that. Mainly because I myself have been looking into buying a new wood heater and have been looking into other companies to see if they sell those.

terry.worsham.73 (author)2014-12-25

Great job, but as you had said pretty big burner indeed, but all in all nice job. If you do change it up for the pizza oven please post would love to see what you do to it... Thanks for sharing buddy.

tooday11 (author)2014-12-20


radamquigley (author)2013-09-16

I like the ash box idea. I may have to that on my next build. I have made something similar but it was for a person to dry there pottery. Used the inside of a smaller tank to make the shelf that held the pottery and was able to fire it from three sides and used an air hose to redirect heat back down which also helped keep the fire burning hotter. Great project you have done here.

dugthegreat53 (author)2013-09-09

can you use an old gas water heater in place of an electric one?

Dave2340 (author)dugthegreat532013-09-09

If the heater is based on a metal cylinder then certainly. On the issue of the glass lining, it is starting to flake off. Currently I am looking for some “found steel” (Thanks Phil) suitable to make a box as my Pizza oven. Weather here in Australia is rapidly warming up so won’t be using “Ned” for a while. Hopefully the steel required will cross my path in the summer months and can be cooking Pizza’s by Autumn. Thanks for all feedback, really appreciated. Cheers Dave.

SIRJAMES09 (author)2013-07-27

AWESOME IBLE!! TY for sharing Sir.

about the glass lining.
with a hot enough fire(400 - 500 degrees) it(the glass) should crack & break away...or tap on it while it's hot & that too should cause it to break away.

Either way, I think it to be a smart idea to remove the glass lining B4 cooking any food.

old_alex (author)2013-04-03

I would assume this is "glass lined" as are most (looks kind of shiny in the pictures).
How thick is the glass layer and can it be removed?
While it looks like a candidate for a smoker or a pizza oven as you suggest at the end, I would advise against is due to the glass flaking off.

Dave2340 (author)old_alex2013-04-04

The glass is about 1mm or so in thickness. It is very tough and takes quite a bit of grinding to clean the surface for welding. With a fire in it I would expect there will be a lot more expansion than normal. The question now is will this crack the surface and will It break free. I'm not jumping in to the next stage too quickly. I feel it would be best to use as a heater for now and inspect the lining later to see how it has coped. Since posting I have cut off and sealed the input/output ports (5) on the body.
If it looks even slightly off then at best I will need to seal off the oven area. Worst case is I will just have to accept it as a oversized outdoor wood heater - no problem there!
I will update though and let you all know if it is feasible.

spylock (author)2013-03-28

I would think one would make a good forge also.

EricHi (author)2013-03-24

You really did a great job - nice looking too!

rncbme (author)2013-03-22

Great Job Dave! Not so much since the price of metals has soared but I used to pick up angle-iron bed frames at the local dump site for free. They are generally a high carbon steel that is hard to cut and drill, but hey, free is free. I've made all kinds of frames and mounts from them.

actionjksn (author)2013-03-22

Its actually spelled "steel"

foreverdisturbed (author)2013-03-21

Cool Recycling Project. Nice Work.

jsolterbeck (author)2013-03-21

Ha ha! First thing I thought of when I saw the pics at the top was "PIZZA!" Funny, all roads lead to Rome sometimes. I'm gearing up to make a wood fired as well, I just liberated two 36" stones from a commercial pizzeria-style steel oven, and I'm getting the brick from this place in Monterey. Mine's a little more traditional, albeit small. Good luck, can't wait to see what you come up with!

Phil B (author)2013-03-18

Very nice. Isn't it fun to take scrap and make something useful because you can weld?

Dave2340 (author)Phil B2013-03-18

Phil by day I'm an IT consultant servicing computers for small business clients. Great job really but not at all physical. Which i why the welding and tinkering is so rewarding to me. i hope my first Instructable is well received, i have plans for a couple more developing in my head. Thanks for the first comment on this project.

Phil B (author)Dave23402013-03-18


I lived in Chattanooga for a few years. Someone there told me about a local cardiologist who talks with stressed executives. For their own good he sends them to a welding course because it is relaxing. I just retired from 40 years as a Lutheran pastor, which involved dealing with people. I always enjoyed my tools because in an hour or two, I could see the results of my work. It was seldom that way when dealing with people.

I first got a welder about 15 years ago. I learned by reading books and posts on the Internet, and then trying what I had learned. Now there are good videos on YouTube and elsewhere. I always thought welding was like alchemy. You could take scrap and make something valuable from it. My welds could be legitimately criticized on a number of fronts, but none have broken so far, either.

Congratulations on your first Instructable. It seems people with welders are always looking for project ideas. Yet, it is difficult for one person to suggest something for another because needs and interests are so different. I have done some Instructables that make decent welding projects for those whose interests are along those lines.

When I began posting Instructables, I thought I might have ideas for a dozen or so. But, after a while there were considerably more than that. I continue to think I have published the last idea I will ever have, but a new problem arises and needs to be solved, so I document it with an Instructable.

I look forward to more Instructables from you.

Jackn7 (author)Phil B2013-03-21

I like all kinds of projects like this, as I have this inherent desire to re-purpose things instead of filling up a land fill.

De-soldering parts from old computer boards and power supplies, then building something from those components. A recent instructable that went about salvaging a Microwave Oven Transformer and converting it to a Spot Welder gave me an idea for converting an old transformer that originally came from a Shrink Wrap machine for the same purpose. :)

All this stuff is great!

I also love to work with wood.

Making use of what you have available is always a great brain exercise! ...and you are right, much more relaxing than dealing with people... hah hah!

wisconsinjimmy (author)2013-03-18

Not to put a cloud on your project but you should know that welding galvanized metal is extremely hazourdous and the effects would make you cringe. Please scrap the galvanized stuff it is not worth your health. I would suggest looking around for an pld 100# propane tank, remove the valve after you make sure there is no propane in it and fill with water then empty and you are good and safe.

Dave2340 (author)wisconsinjimmy2013-03-18

In the research for the project the issues with gal came up quite a few times. I used a grinding disc to clean the area well before starting. when actually welding i was in the open garage doorway with a fan blowing across the work to minimize the fumes. Also welding is short bursts also helps. Thanks for the concern, definitely needed to be clarified.

streetrod5 (author)2013-03-18

Dave, great job, good, clear pictures and a fun build! I've always wondered what a water heater looked like inside, but was afraid to ask. Very useful project. I bet you could run water pipes through to provide a little extra hot water (say for an outdoor shower, or to wash the car).

Phil B (author)streetrod52013-03-18

We replaced an electric water heater a couple of years ago. I did not think much about using the tank like Dave did; but, the water heater was in the basement and the tank weighed a lot, so I cut it up and got some money for it at the scrap yard. I did save the outer skin of the water heater and have made several useful things from it. Things like this are "found steel."

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