I know the original question has been answered but it seems people are still debating the merits of various solutions so I'll throw in my opinion here too.
I had a 19x22 attached garage on my last house. Half had 9' ceilings and half was 11' with a bonus room overtop, only one wall connected to the house and it had a (poorly) insulated door. I installed 2x1500W ceramic radiant heaters on the ceiling. When I wanted to go work out there I'd just turn both heaters on and head right out, no waiting. Radiant heaters are mostly about heating you and not heating the entire space (although they will do it if given long enough), so in my case I put them on the high part of the ceiling and aimed them so that they covered a little more than that half of the garage. If you were working under them you could head out there with no jacket and work comfortably even when it was stupid cold outside. They were cheap to buy (~$50 each) and cost very little to run because for the most part they were only on when I was actively working out there, so maybe 30-90 minutes at a time. In my case I already had a subpanel in the garage so running the electrical was trivial.
The big downside to this solution is if you have to work under a car or something where you don't have line of sight to the heaters, then they basically do nothing for you. A couple times I ran them for 3-4 hours before going out to warm up the entire garage and they did an acceptable job of that but the slab was still stone cold and I suspect they'd take 24 hours to fully warm that up.
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Originally Posted by Yolobimmer
