Turning a gas bottle into a log burner

With the nights drawing in, sitting in the garden without some form of heater in the evening is starting to become less appealing. Combined with an abundance of wood as a result of the several trees I felled this summer, building a log burner seemed like an excellent idea. I decided to base it on an old 7kg gas bottle that was lying around; it’s a nice size and shape, and made of thick, good quality steel that won’t burn through easily.

Before taking power tools to a gas bottle it is vital to ensure that there is no gas left in the bottle. Simply releasing the pressure wont do; you must remove the valve then fill the bottle with water to displace the remaining gas. The bottle should remain filled with water until all the gas has dispersed and then emptied and left to stand to allow any remaining traces to dissipate. After all of this, the bottle will still smell of ‘gas’; this is to be expected, the smell is caused by an additive that leeches into the steel.

Once the bottle was safe to work on, I removed the handle/valve protector ring using an angle grinder.
Mike cutting off the top ring with an angle grinder

Next I made the fuel/air opening on the front; I marked out a D shape and started the cut with the angle grinder, then completed it with a jigsaw.
A D shaped hole cut into the top of the bottle

I had a rummage around for something to make legs out of and came across 3 mini fence post spikes.
One of the mini post spikes
The bottom part of the spike is constructed from 2 tapered pieces of angle steel welded corner to corner. I cut these off just below the join with the box section, and ground most of the welds away. I could then then split the spikes into their separate parts with a hammer and masonry chisel.

In order to make the burner more portable, I opted for removable legs. This was achieved by cutting some tabs from a piece of the box section of a spike, into which I drilled and tapped M8 holes. I marked up positions on the bottle to weld the tabs on, and stripped the paint ready for welding. A leg tab being held in position by a magnet against the gas bottle

Using my MOT welder (which I’ve made a few improvements to, detailed in an upcoming post), I welded the tabs on.
Me mid-weld, attaching a leg tab

To fit the legs, I trimmed the tops and drilled bolt holes; seeing as the gas bottle now had legs, I removed the bottom stand ring (again, using the angle grinder). The box section pieces of the spikes looked perfect for a chimney, so I cut a suitable square hole by dropping the angle grinder directly down into the bottle.
The gas bottle with the bottom ring removed and a hole cut for the chimney

The only thing missing now was the chimney; I took the box section parts from the 2 spikes that I had used for legs, clamped them end to end with some pieces of wood and welded them together.
The two pieces of box section clamped ready for welding

At this point, I had something that looked like a log burner; to make removing the paint easier, and see how well it worked, I fired it up. It lit nice and easily, using a bit of newspaper and some split pallet wood.
The burner being fired up for the first time

While it did burn well, the chimney didn’t draw as well as I’d hoped. The first thing I did to improve this was to simply extend the chimney; I welded the box section of the third spike on the top for something like a 60% increase in length.
The chimney with a third piece of box section welded on

I also improved the mounting of the chimney onto the main body. Previously it had simply been pushed in, and held in place by friction; this was both a bit precarious and the extension into the body interfered with airflow, which reduced the draw. I welded on a couple of small plates with holes in, and used an old tent peg to pin the chimney in place. It still extends into the body to ensure a secure fit, but much less than it used to.
The chimney pinned into place with an old tent peg and a bracket made from 2 pieces of steel plate

Another issue I discovered was that, while the legs provided excellent stability side to side, the burner was able to fall backwards too easily to be safe. I solved this by adjusting the legs and tabs such that the legs extended out backwards; in order to maintain the height I simply bent the tabs inward, using the leverage of the attached legs.
The burner with the rear legs adjusted to provide more support to prevent backwards toppling

I also built a cowl to prevent rainwater filling the stove when left outside; I cut a piece from the handle ring and crushed it in the vice to increase its curvature, then bent some coat-hanger wire into a couple of supports. Welding the wire was a somewhat dubious affair; my welder is much too powerful for this type of job, resulting in welds that only just hold and are very inaccurate. It does work, but I plan to revisit this and do a better job once I’ve sorted current limiting on my welder.
The removable cowl inserted into the top of the chimney

All that remained to do this point was to apply a coat of paint. I used wire brush attachments for the angle grinder and power drill to remove the original paint; this took a long time as both gas bottles and post spikes are designed to withstand rough treatment outdoors.
The burner, stripped of paint, about to be painted

I then applied a couple of coats of stove & BBQ paint, left it to dry then fired it up to cure the paint. I did have an issue with a bit of the paint around the fuel/air hole and chimney flaking off, but I suspect this is where flames were licking it due to building the fire far to hot (with the help of a little bit of engine oil). I cleaned these areas with a wire brush and reapplied paint and have not had any more problems. The paint on the legs won’t have got hot enough to cure, but this does not seem to cause any problems; it looks and behaves just like standard black paint.
The completed stove, with cowl, fired up

The new chimney draws much better, and there is no longer any risk of the burner falling over backwards. Once a decent bed of embers is built up, it works very well; the wood burns pretty cleanly, and what smoke there is gets drawn up well. It currently makes a very nice patio accessary, with the potential to make a good shed heater in the future.

10 thoughts on “Turning a gas bottle into a log burner

  1. Anonymous

    This nearly answered the question of how to get the gas out. How do you remove the valve to put the water in.

    Reply
    1. Mike Post author

      If the bottle is like mine it will just unscrew; I used a big adjustable spanner combined with brute force and ignorance.

      Reply
  2. Steve

    How do you remove the valve. Basic question, I know, but as this is such a big safety matter it’s best to ask.

    Has anyone tried using the lighter gas bottles used for inflating party baloons? How would you get the valve off those too?

    Reply
  3. Don

    Valves are very difficult to remove. So don’t. Just fill with water with valve open – takes a while, but will fill. I cut the bottle with water still in it. It started leaking out as the hole went right through, nowhere near angle grinder. Just don’t have your lead plugged into extension too close by…

    Reply
  4. Tom Heald

    I was given a half full 15kg bottle the other day, I took it to a vacant block and turned the valve on then turned the bottle upside down to empty it fast, I left the valve open for about 30min and blew into it a few times, after another 10 or so minutes I lit a rag on a long stick and put it to the open valve ….. Nothing, so I ground the brass valve at the thread off as brass doesn’t spark as much and I’m still here’, trying to get the valve off these bottles is almost impossible and filling with water would take a week, just be extremely careful, I’ve actually done this to two bottles now.

    Reply
  5. Anonymous

    Be persistent…. the valves do eventually unscrew. Mole grips or similar and a hammer (or a long bar) do the job.

    Reply
  6. Jake Farish

    To everyone asking about the valves, I recently removed a few in a row and found the easiest way way to lay the cylinder down on its side, place a drift against the outside edge of the valve (make sure you’re hitting it the right way, left loosey, righty tighty) and apply gentle persuasion with a lump hammer. Make sure the drift is against the brass to ensure you don’t get any stray sparks. All of my valves were unscrewed in a few minutes max bar one, which shattered. I just finished shattering it so that I could get the water in easily.

    Reply
  7. Steve

    Sounds good, but I’m not familiar with the word ‘drift’ in this context. I can only emagine you mean a spanner.

    I would be interested to know if anyone has made a wood burner using the party balloon gas bottles too. And if so, how they handled the valve issue.

    Reply

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