I had one of the kerosene jet engine looking heaters and it worked OK, it requires a special thermostat and you can buy a liquid product that will eliminate the smell. I wouldn't recommend it but it worked OK.
Be careful with portable kerosene heaters. If they are not vented, they will be putting CO (carbon monoxide) into the room. That's a problem, because it combines more readily with your red blood cells than O2 (oxygen). Meaning that even if you have O2 in the room, you can easily get CO poisoning.
They also have a propane jet engine looking heater my friend had one and it was pretty loud but did a good job.
An unvented propane heater is a step up in safety from a Kerosene heater. The byproducts of a properly functioning propane heater are CO2 (Carbon Dioxide) and water vapor. CO2 is not great, but is less hazardous than CO. In addition, most heaters designed for indoor use have an oxygen depletion sensor, which will shut the heater down if the CO2 concentration rises to near unsafe levels.
I have both a "torpedo" type propane heater (which as you noted is rather loud), and a "Big Buddy" propane heater. I prefer the Big Buddy, since it's quiet, and will run even if the power is out, so useful for freeze protection in a power outage. I run it with an adapter off of a 20# propane tank, rather than the little canisters that fit in its internal compartments.
The drawbacks of an unvented propane heater:
- Even with an oxygen depletion sensor, you need to be aware of CO2 issues (I crack two windows in my shop when running it for ventilation.)
- Since one of the byproducts of propane combustion is water vapor, you can build up a lot of moisture in the room when running the heater hard. I got to the point where my walls were dripping on a couple of occasions.
You can also buy a 120VAC 11,000 BTU window AC unit with a reverse heat pump, I had another friend who had one in a detached shop about the same size shop as yours.
If I was going to buy something today I would buy the AC unit with the heat pump. It is quiet works pretty quick and is an all season unit. If WIFI you can remote start a short time before going to the shop.
I did not realize they made portable window units that were heat pumps that worked for heating as well as AC. I may have to look in to one of those. I looked at permanently installed mini-split heat pumps, but never made the jump for two reasons:
- I was concerned about how frequently sawdust from various woodworking projects would clog it up
- I have yet to find one with a setting that will turn down low enough in heat mode. I'd like to be able to set for 45˚F when the space is not in use just to protect from freezing. Most won't go below 55˚.
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Our shop is 24'x26' with 10' high ceilings. It is VERY well sealed and insulated. We had 6" of insulating foam sprayed in the walls, and at least that much in the ceiling before putting up the sheet rock.
We currently heat it with two electric space heaters. One is the
oil filled radiator style with three heat settings (600, 900, and 1500 Watt) with a thermostat control. The thermostat is not calibrated, but after a while I figured out where to put it so it will come on at 45˚F as a "freeze-protect" mode. Works well, since sawdust accumulation from various wood working projects don't phase it. If it does get a coating of sawdust, a quick blast from the air compressor takes care of it. Once the room is up to temperature, we can generally get by with just this one to maintain a comfortable level unless it is really cold out. (that might be a stretch for most workshops of this size, but this one is tight and well insulated enough that it does OK enough till the outside temperature really drops.)
The other heater is one of those old "
milkhouse heaters" with electric resistance heating coils. We use this as a booster to warm the room up more quickly, and as extra heat when it gets really cold out. It also has an uncalibrated thermostat. When the shop is not in use, I usually set it to come on at a bit lower temperature than our oil-filled heater as a back up.
