-- Last Updated: Feb-06-13 1:20 PM EST --
You will have no trouble finding a kerosene heater that can keep the place toasty warm, but not all models and styles will do the trick. I once had a blower model (the kind with a tubular shape that sounds like a tiny jet engine) which I think was rated for 150,000 or 175,000 BTU, and it would get a 4-car garage (no insulation and open attic space) up to 70 degrees in a very short time on a cold winter day. I'd end up running it for 15 to 20 minutes at a time, with the "off" periods being a lot longer than the "on" periods. You can get thermostats to regulate how they turn on an off, but I just did it manually. I could have used a much smaller unit and it would have done the trick, but while running a larger proportion of the time. In your situation, a blower-style heater of much smaller capacity (75,000 BTU?) would probably be plenty. I have never heard any positive comments about non-blower styles of kerosene heaters except when used in very small enclosures, but someone else may say otherwise.
The PROBLEM you may find with a kerosene heater that's big enough to keep the space warm, is that the exhaust is unpleasant over extended time periods, and anything in the garage that is cold becomes a condensation surface for all the water vapor that's in the exhaust (the windows will be constantly dripping, and all your metal tools in the building will be soaking wet until such time as they become about as warm as the heated air, and that takes a long time). You might also want to research whether any of your adhesives or resins cure improperly in the presence of combustion by-products. If the heater is small enough that the exhaust presents no problems at all, it probably won't produce enough heat to make the garage very warm.
I used that big kerosene heater for a few years but eventually got sick of dealing with combustion exhaust and installed a vented natural-gas heater. However, for short work periods I didn't mind kerosene fumes too much.
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