I've only had to deal with temps in the low 30's but I can tell you that walmart sells a little heater with a built in fan for $15 that can get a small room really toasty. One of the few times something cheap and imported actually works better than I expected. I bet two or three would give you nice heat all around the garage. They are only about 12"x 5" x 5" and sit nicely just about anywhere. It's a cheap way to go and if you dont use it often and just want instant heat wherever you are it might be a good option. You can point them wherever you are working and they really crank out heat for how small and cheap they are. ive had mine in my garage for about 4 years now and still works like a champ. I also use it as my heat gun quite often lol.
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