Heating the entire air space in a garage is incredibly inefficient. It takes forever to work out the coldsoak. Then you pick up a tool.... zikes! The damned thing is freezing.
For only a few $ you can buy a couple of 150-300W infra red lamp bulbs,(often called brooder lamps), used for keeping chicks warm.
Much like being outside on a cold but sunny day, your shop can be quite cool, but the radiant heat keeps everything it touches warm. Several of the outdoor hot spring pools out West use them to keep the walkways warm between change rooms & pool.
I use a couple to keep the granite floors warm between bathroom & sauna.
The best heat, though costing more) is an overhead radiant heater. They keep everything, including the concrete floor comfortable enough to work in shirtsleeves. The cost for natural gas to run them is a few dollars a month.
Free Shipping - Mr. Heater Garage/Shop Radiant Heaters with qualifying orders of $99. Shop Heaters, Non Automotive at Summit Racing.
Every ice rink here uses them to heat the stands, you can watch the game sans coat.