I have three separate garages/shops I heat occasionally in the winter here in northeast Ohio. In each one I use a direct vent gas furnace made by Williams. They are about 7' tall and 14" wide. Easy to mount, combustion chamber draws air from outside and is completely sealed off from inside air, so no worry about blowing up when your cars' gas tank leaks. They are very quiet, have a two speed blower, and the hot air comes out of the lower part of the unit. In the dead of winter, they will heat up a three car garage that is insulated, in about fifteen to twenty minutes. Very quick and economical to run. 62000 btu input and around 83% efficiency.