This is what I was thinking about originally. So what kind of single burn heater? I saw some in Home Depot but did not know what size? Any recommendations?
It's a 15,000btu tank-top model from Harbor Freight. Search it on their site.
Regarding carbon monoxide, I agree. I have a detector in the garage and only run it for a few minutes at a time. The electric space heater maintains the garage at a temperature that's comfortable in jeans and a long sleeve shirt.
My garage is insulated, including the door. I live in St. Louis so our winters are about the same.