My garage is small, 24x24 and it is semi insulated, the ceiling, peak, overhead door, and two of the walls. Ihave one of those 50,000 BTU natural gas heaters mounted high on one end. I can warm it even on the coldest days into the 80's if I want. I usually keep it in the mid 40's all the time and turn it up when I'm out there. In the old days I used to use one of those Dual Mr Sun Radient heaters on a propane bottle with a box fan behind it to move air. And that would make it comforatable. The NG heater is the way to go if you can.