I've got the same issues. My garage is has no insulation to the attic, and I'm not sure about the outside wall. Right now I have a 5kw electric heater in the upper front corner. It knocks the edge off but takes forever to warm up. When it is 20 out I can get to about 45 maybe 50. I'm going to add a LP torpedo heater to get up to temp in about 15 minute and then the electric will hold temp long enough. Eventually I want to put it natural gas up by the ceiling or maybe one of those radiant bar heaters on the ceiling if I can find one I can afford.
I need to insulate the attic, but I have so many car parts up there it would take me a week to clear it out so that may wait till the car is back together
