I plan on tossing an overhead 220v electric unit in my garage at some point. With a simple oil electric space heater I can maintain the temp decently in there.
Biggest improvement for mine, insulate the crap out of the walls, and ceiling, then seal it up well with sheet rock. That in itself cut down the wind chill immensely, and also stabilizes the temps.
That being said, my garage can be toasty, but the concrete slab is always frozen. If you can swing the in ground heat, do it.
