If I want to work in the upper garage on one of my cars or tractors in the winter, I have a 45000 btu propane heater I run for about 15 minutes at a time to bring the temp. up to 65-70 degrees. The garage is well insulated, and even today with the temp at -20 and the wind chill at -50 it stays at about 45 degrees without heat. Garage is 36 x 24 with 9' head height. My lower shop is under the garage with drive in axis from the rear. Being completly under ground level it stays about 55 degrees in the coldest weather. I can also open doors on both ends to get heat from the lower level of the house. I have a 2 speed two level propane heater, 45000/65000 btu, that I use when I come down to the shop on the cold days
Takes about 30 minutes to bring the temp of this 1200 square foot space up to 65 degrees. I keep a carbon monoxide detector above my work bench, but it has never gone off. I also have a natural gas heater in my paint and assembly room to bring temps up to 65-75 degrees for finishing larger projects. A 15# tank of propane will last me most of the Winter.I find propane to be almost oderless when burning, however you can smell a leak if your fittings are not tight. I have used these heaters for many years with no problems. They are nice to have around if the furnace or power goes out and you want to keep your pipes from freezing. Jim S