[hughc]

When I built my free standing 28 X 30 garage 15 odd years ago I installed in floor heating using a 45 gal hot water heater as the heat source. There are small hot water heaters now available that are probably more efficient and certainly less bulky than my set up.
I turn my system ON in the fall and keep in ON until spring.
The inside of the garage stays at 16 to 18* C all winter long.
It is just as comfortable as the inside of my house and is perfect to do whatever guys want to do in the middle of winter, (that you aren't allowed to do in the house)
There are frugal people out there that think it's ridiculous to keep my garage that comfy all winter long but my argument is that at my age, the extra $125/ month for electricity isn't going to make any difference. Once you're gone, you're gone.