I'm using a 30,000 btu blue flame walmounted propane heater. It heats up my area relatively fast and doesn't take much to maintain. My shop is 30 x 30. I have 8 1/2 ft ceilings & all walls & ceiling are R19 and drywall. I have 2 100 lb. tanks behind my garage to run them. pretty efficient and quite cheaper than electricity.