So i came up with a very good idea, and very cost effective idea to heat a 40x80x 16 tall shop. Do you have propane or natural gas on site? If so, so get a grain bin dryer system. Cost is about 4500 bucks, for a 2.8 million BTU unit. Moves a TON of air and uses less wattage than a traditional shop unit and less propane than a traditional shop unit. The catch is.... it is VERY LOUD. Granted it mounts outside the building but it will annoy the **** out of your neighbors if you have any close.