I am working in a 36' X 36' garage that is insulated but has more than its share of air leaks in it. This year I got a good buy on a 75.000BTU free standing gas furnace with blower in it. It will heat the garage, but if the temperature is under 25 the cost of gas to get it warm and keep it warm is astronomical. And if there is any appreciable wind, forget it. But since I love to build and tinker around so much, I am going to drape an area large enough to enclose my stuff in, and see how that works. Maybe the back 15 feet or so all the way across (15 X 36). That will also eliminate the leaks around both overhead doors.