rcmodel
Member in memoriam
What he said.If you have forced air, is there any chance your furnace or its ductwork is in or near the garage? Could be a simple solution
A HVAC guy can probably put a furnace vent and cold air return in your garage way cheaper then an industrial strength propane or kerosene heater and fuel will cost you in the long run.
And it won't fill your house with fumes and carbon monoxide and kill you if you forget to turn it off when you go to bed.
rc