Personally I use a kero "Reddy Heater" to occasionally heat my garage. We
have nat. gas heating in the house, but the piping is not convenient to the
garage, and it would be a major install/expense to run a line. For the few
times I use it, it just isn't worth it.

You can get propane Reddy Heaters as well. They are a bit noisy, but it
doesn't bother me in the garage. I built a little thermostat that cycles it
on and off (you can also buy them, but I didn't want to spend $50). I
usually keep it about 60 degrees when I'm working out there, which is fine
for me. Here in MN we can see temps sub-zero and my 60,000 BTU unit can
heat up the garage in about 15-20 min.

-Tim