My neighbor heats his garage with wood stove also, and it does a good job keeping it warm, but he has to fire it early, and then wait a few hours before going out to work. Then there's all the summer trips collecting wood so he has enough to keep his house and garage warm through the winter.
I'd rather be working on my car than gathering, splitting wood. Especially in the summer when I want to be driving the hotrods, and not driving a truck out to gather firewood! Not to mention wood cutting permits, and the price of gasoline to go cut it!