Hi Brad;
I have the Combustion Research Company's Omega II natural gas fired infra-red tube heater in my 2.5 car attached garage with 2.5 exposed walls.
I set the T'stat at 55F, the unit has kept the garage worm enough to work in a sweat shirt here in SE Michigan without trouble. I have not insulated the exposed walls or ceiling, if I used the garage more I might think about it.
I have insulated my OH garage door with rigid foam and that helps.
The reflective heat shields rattle, but I fiddle with clamps to dampen that out.
Here's some pictures.
Mike