I've got a 26x36 garage that is well insulated and I installed a natural gas unit heater rated at 45000 btu input.It's 80% efficient and will run you out of here if I turn the stat way up.I vented mine through the wall with b-vent pipe and a wall thimble.I just leave it on all winter with the stat set at 55.No matter what kind of heat you use,if you dont keep temp constant and heat only when you're in it your stuff is gonna rust.
Not only that, but like I used to tell a friend who tried being "very cheap"....... -- He would turn the heat OFF in his house, all day long, and only turn it on when he was freezing! And I would say dude, you waste more gas turning it on cold and making the damn heater work harder in spurts than you would if you just left it on at a constant temperature all the time. But anyway, in my garage I'd have to go with electric heat.. with the price of propane up here..... it's just cheaper.
