Need garage heating ideas that hopefully don't involve combustion. Or, if they do involve combustion, then the exhaust is easy to remove and not thru the roof. Space is about 20' X 30' i am using a combination of kerosene, electric, and leaving the door to rest of the house open and working in the garage for a few mins, going back inside the house to warm up, going back into the garage, repeat etc. This can work ok, if it's not too cold outside, but if it's sub 38-ish, then i am thinking there is a better way? Thanks.