I'm debating putting some sort of heater in my garage.  It's 28x30x12 with north facing garage doors.  There is living space above the garage which makes it impossible to vent through the roof.  It doesn't need to stay toasty warm.  38-40 would be fine which usually isn't a problem but these cold spells cause issues.  I have propane close by or could go electric.  Suggestions?