I have a bigmaxx natural gas heater it cost me around $120 annually to heat the garage at 70 degrees during northern Indiana winters. I purchased a 5000watt electric heater from rural king for a backup when the gas furnace sometimes doesn't work because of a plugged vacuum switch. I heat a 990 square foot garage with no problems. The detached garage is very well insulated R19 in walls and R30 in ceiling. The bigmaxx 50k btu cost under 400 and a case of beer to the son inlaw to run the gas line and the electric backup with a fan cost $78 at rural king.