I used one of the dual burner units that attaches to the top of a propane tank last winter for the first time. It heated my garage (about 625sq. ft.) quite well. I liked the duals because you could run one or both. If running propane CRACK THE GARAGE DOOR, propane is heavier than air and it has to vent or the fumes WILL make you sick, as I almost found out the hard way. But if you can afford it an electric heater fan forced or radiant would be ideal, just be prepared for the electric bill based on size of unit and amount of use.