My garage is 30 x 32 or 960 sq ft. I put in a 50k btu BiggMaxx propane hanging propane heater. Garage has 2x4 insulated walls and R30 in the ceiling. I only turn heat on when I’m out there and only to 50 degrees. If your working with a sweatshirt on, it’s plenty warm. The heater really doesn’t run much. I’m in NE PA, gets pretty cold in the dead of winter.