Heating a workshop/garage

It has to get air from *somewhere* and unless your workshop is of infinite size it will be drawing that air from outside, either via a dedicated properly sized vent or (more dangerously from a Carbon Monoxide point of view) from around cracks in the door/windows/framework. That air, being continually replaced as combustion occurs, is usually very moisture laden (at least in the UK) and will, when the stove is shut down, cool and eventually deposit all the moisture held in that 'fresh air' over everything.

Of course if you can source external air, direct to the stove, and exhaust air direct to outside, and only use the hot surfaces of the stove to heat the workshop then you might, with unlimited supplies of fuel, have a cheap source of heat. Think of it as similar to a room sealed boiler hanging on the wall of the kitchen. It keeps the room warm(ish) with the heat lost to the boiler casing but despite burning lots of gas or oil it doesn't fundamentally alter the humidity levels in the room.

Such an approach will IMHO never compare to the comfort and luxury of background underfloor heating fed off the main central heating circuit of the main property, nor will it compare to solar air heaters in simplicity and zero carbon emissions.

It's not the combustion products, it's the fresh air draw especially when you have intermittent use that is common in the amateur workshop. Maybe with JS the extended length of burn with long days and the mass of the machines helps to some extent but the humidity levels will almost certainly go all over the place. A few years ago I measured them over an extended period in a commercial joinery workshop that occasionally had serious condensation problems unless they left the workshop doors open. I rejected wood burning for my own workshop for precisely that reason. I have access to huge amounts of free well seasoned scrap wood but I'd *never* use it in any conventional workshop stove.

A water output of roughly one for one is pretty significant in my view.

it's the fresh air draw especially

It is certainly the case that, especially during winter, the air inside a house contains vastly more moisture than outside air, although it is usually at a lower RH.

Is it your conjecture that this is not the case in a workshop (assuming a similar 'room' temperature)? Maybe because there are few if any moisture generators in the workshop such as people, dogs cooking etc.?

If not then any air drawn in to the workshop to feed the fire would acually reduce the water content not increase it since incomming air contains very little water even though the RH is high outside.

Richard

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It most certainly IS the combustion products that are the major problem, though I daresay you are correct that the indrawn air will contribute a little to the overall level of moisture. Simple school chemistry shows that combustion of any fuel containing hydrogen will produce water, (2H2 + O2 =

2H2O). Unless that moisture-laden exhaust is vented outside the building, it will enormously increase the water content of the air.

As Don and others pointed out, the question of whether condensation occurs is then a matter of relative humidity against dew point, and the degree of cycling caused by intermittent operation.

Cliff Coggin.

It would be worth doing the numbers on this, but my guess is that the moisture brought in from the outside is a minor problem compared with the moisture exhaled and perspired by the engineer(s) in the workshop.

You could fix that by wearing a fully seald CBW suit & breathing kit I guess ;-)

Regards, Tony

Charles Lamont explained on 14/01/2010 :

Nor I, apart from the fact that it will be drawing its combustion air in from outside, through what ever ventilation it can find. Perhaps better to organise a more direct method of air entry, close to the burner?

Dirk explained :

I found the US plans to make one from an old steel HW tank, but nothing for reusing old 12Kg gas bottles - which was what I was planning to have a go at - have you a URL?

Het is zò dat Harry Bloomfield formuleerde :

Hi Harry, correct. I used whatever was at hand, so bottles. Mine looks much like Roger Sanders' heater, type MEN(ew). The original is the ME type. MEN is linked on that page, also some forced-air ones.

Dirk submitted this idea :

What did you do, weld one 12kg on top of another? You can get much larger (taller) red propane bottles. I was thinking of a single 12kg bottle, I just need a small heater to take the chill off.

Are UK garages likely to give the old oil away, like in the US?

Not if you vent the combustion products outside it isn't!

That's what I said, didn't I?

Cliff.

Harry Bloomfield schreef op 15-1-2010 :

Yes Harry, I cut off both tops to get rid of the valve sections. Did not weld them together yet to get inside for changes, etc. Made a flew and an intake of 100mm both. Contacted Roger Sanders to get data on diameters, relations. I assumed a ratio between flew/intake and circomference of container. Roger says they seem more or less absulute. I am located in the Netherlands. Best regards, Dirk

Thanks..

This is a link to the waste oil burner i'm in the process of putting together, it may be of interest.

I found the US plans to make one from an old steel HW tank, but nothing

for reusing old 12Kg gas bottles - which was what I was planning to have a go at - have you a URL?

I'd be surprised if they did - they're probably committing an offence if they give it to anyone other than a registered waste carrier.

Russell

Na rijp beraad schreef alspeed :

No url, sorry, used some data of Sanders'MEN(ew) heater, rest was dictated by the bottles. Dirk

My local garage gives you as much as you want. I keep a gallon on hamd for oil blacking, but apparently a lot of the even-older generation take plenty of it every year for painting their fences in place of creosote.

peter

My wood burning stove runs intermittently, when it's cold it goes on and often stays on but goes out every evening. The shop is actually uninsulated, brick outer, block inner, no cavity and a concrete floor, no barrier as the floor was already there.

It's in two sections, the oldest part, an old stable, is 9" brick with tiled roof, no insulation. The newer part is brick and block with a sloped felt roof, again no insulation as I was strapped for cash when I built it and as usual it's one of those jobs that every winter you are going to do next summer.

God knows how much steel and cast iron there is in here as regards machines and stock, at least 7 tonnes of steel on the racks. Total must be over 25 tonnes ?

I never oil any of the machines other than the general run of using them, they get switched off, lights out and that's it. I get no rust full stop.

In this weather I'm running the shop at about 20 to 30 degrees and all the wood is free although some has to be collected from 5 miles away which I usually do over a weekend and fetch a full van load, this also runs a stove in the house.

Non use doesn't seem to have any effect although longest time unattended is usually only a week and maybe any time of the year, Last Christmas it was shut for 10 day with no heat at all whilst I was in China, again no rust or weather damage.

John S.

Here are a few URL's I have come across...

and the only one I could find with regards to the burning of waste oil...