I use a Propane heater in the garage in the winter.
To burn propane I need 2.5 sq.ft. of open area to the outside air which is having 1 garage door open less than
3". I usually have a fan blozing at the open garage door also. This vents smoke out and turns my garage into a confection oven (it moves the hot air around the 2 car garage to evenly distribute the heat. It works very well).
In a 1 car garage I would think this would work also.
perhaps a smaller fan.
If you need any help let me know.
Plus it keeps his brain warm........:tu