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Workshop Heating


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In the last bout of cold weather (Dec 2007), there was a day where I could not get the workshop above 2 degrees C - which was a bit chilly! I decided to do something about it.

At the same time, Paul Wightman was re-building his woodburning stove for the forge and had installed a back boiler in order to run a few radiators in the further away parts of his workshop - and it seemed to work rather well!

Based on his experience, I thought it would be worth a shot!

My design is based on a pair of scrap 13kg Butane cylinders - although it would scale to the bigger Propane cylinders.


Cut the top and bottom off both cylinders, then cut top 200mm off one. The lower half of this cylinder can be used to make a door for the stove. Cut a rectangular opening in the side of the first cylinder to act as a door.


You will need two bits of pipe - one which will fit iside the other. Weld the smaller diameter pipe to the top of the whole cylinder. This will be the flue. Weld the bigger pipe to the half cylinder. This forms the flue water jacket.

At this stage, it's worth welding some pipe fittings to the water jacket. I used a pair of steel 1/2 BSP connectors which you can get from a plumbing supplier. You can then use a compression plumbing fitting which screws straight into the steel fitting to connect your 15mm copper pipe.

Weld the half cylinder to the top of the whole cylinder. The cylinders are zinc plated as well as painted - so you need to give the weld area a good grinding!

I made a butterfly throttle (like on a carb) using a steel disk inside a piece of steel pipe. the disk was screwed to a bit of round bar which passes through two holes in the tube. The end of the bar just has a handle which you can use to throttle the fire.

I used copper pipe for a meter or so where it comes out of the boiler - then plumbed the rest in push-fit which is ever so easy.


I encapsulated the whole thing inside a 205l chemical drum. I gould have just lagged the boiler with rock-wool or similar, but the outer drum serves two purposes. Firstly it insulates. Air inside the drum, heated by the boiler is then drawn into the inlet to the fire. Thus, some of the energy which would otherwise be radiated goes through the fire again. This makes a decent difference to the exhaust gas temperature and hence the heating efficiency.

Also, I wanted to try Turbo-charging the boiler with a fan on the inlet. Because ash exits through the throttle butterfly, it would be difficult to connect a blower. However, by blowing air into the drum, much of it ends up going into the fire.


I put the whole thing outdoors so that I wouldn't be poisoned by carbon monoxide, it wouldn't set fire to all the rubbish I've collected and it wouldn't take up too much space.

To save myself going out into the freezing cold to adjust the throttle, I fitted a pneumatic remote:


This rotary actuator connects to another similar one indoors (closed loop). When I turn the one inside, the one outside moves in sympathy. Seems to work well!

Why do I need a throttle? Sometimes when the fire is well stoked up, it can get hot enough to boil the water. You need to have a way of turning it down before the contents of the header tank leap out!

Water is circulated using a central heating pump (from a scrap yard):


The pump needs to be placed somewhere it is not going to get trapped air - in a vertical pipe run works well. If you get an air bubble in the pump, it stops pumping and the water boils!

At the moment I'm running a pair of ceiling mounted radiators. One of these was donated by Paul (Thanks Paul) and the other was from Screwfix for £30.


You might think ceiling mounted radiators is a daft idea? However, I have an office upstairs and they heat both the office and the workshop in one hit. I've painted the rads black to radiate better.

The easiest way to drain and fill the system is with the setup shown below:


I have a pair of drain valves on either side of an isolating valve. I can drain by opening one or the other drain valve and fill by closing the isolating valve then connecting one of the drains to the garden hose. the water is forced through the system until it comes out of the other drain valve. It seems to flush most of the air bubbles through as well. I closed the drain which forced water up into the header tank before shutting the inlet then opening the isolating valve to complete the circuit.

The outside temperature at the moment is 3 dec C. Inside however it is:


Not bad me thinks!

OK, it looks a bit Heath Robinson - and it may not be the kind of thing your wife would appreciate installed in your kitchen - but I think it has a certain charm about it. It's Carbon Neutral too!


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My planned workshop woodburner was going to be a lot more simple - like this - but with some sort of back boiler. I'm going to have to pimp my idea like yours now!

That's a nice design for the fire box.

One design detail I forgot was the top of the flue needs a cap or, as in this case, a bend. When it rains, I found the fire almost impossible to get going. Addrd this to fix.


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  • 3 weeks later...
That's a nice design for the fire box.

One design detail I forgot was the top of the flue needs a cap or, as in this case, a bend. When it rains, I found the fire almost impossible to get going. Addrd this to fix.



i thought you would have gone for my chimny top



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Si thats sound.

In our last house we had three log burners, one heated the water and the other two heated various radiaters throughout the house.

The one log burner did not have a pump but simply relied on hot water rising then cooling which then sunk and therby made the water flow through the system. Took a little bit to get started in a morning but once hot it worked fine without a pump!.

What are you burning, wood or coal.

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Brilliant idea :)


Cut the top and bottom off both cylinders, then cut top 200mm off one.

in the interests of safety, what is a safe way to do this? Presumably grinder or gas are a bad idea for cutting up old gas bottles :huh: I have even been a bit nervous using a cold chisel to cut tops out of old 45gal petrol drums in case of a spark!

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Steve, I have used a grinder to cut gas bottles with no problem. You need to ensure they are properly purged first though - leave them open to atmosphere (in my case for about 3 months before I got round to doing anything with the bottle) and then for good measure I filled it with water.

Cutting was no problem, apart form the noise - they ring pretty well!!!

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The principle is to replace the flammable gas with an inert substance.

In practical terms the method and the substance can vary.

When repairing or modifying motorcycle fuel tanks the accepted method is to place the tank filler opening on a van exhaust, preferably diesel, and run the van engine at tickover for 15 minutes.

For a large tank, as used here, this could be combined with the fact that the propane / butane is heavier than air, so the tank would be best upended, having first removed the valve, and the exhaust gas piped into the tank.

Personally I'd remove the valve and wash water through the tank, then I'd leave water in the tank to a level just below where I wanted to cut, and use the angle grinder.

Once the top is removed I'd lower the water 200mm, and cut again.

An advantage here is that the weight of water stabilises the work piece.


PS, I see Mark used the same method, in less words!!

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I'm game but buyer collects could add to the cost considerably :D

By the way, I have approx 250 tonnes of firewood if anyone is interested. £10 a tonne buyer collects.

I love the thinking my workshop has an electric oil radiator but i might try this

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  • 1 month later...

We are working in Burnham on Sea this week (28th - 4th) if anyone wants any firewood FOC.

I can deliver local or anywhere near to the M5 on the way back to Wolves or you can collect.

It will be cut small enough to pick up manually but will need splitting/cutting.

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