I have a 24 by 24 garage and got a 220 electric heater from menards last winter for about 270 bucks. I insulated and sheetrocked the walls and with that little heater it warms up nice and stays warm. It has a built in thermostat that helps to keep it a whatever temp you want. Only drawback is you need 220 in the garage- I wired it in when i was putting insulation in. I felt much safer having that on then a gas one.