I have a 60x60 shop partially insulated that stays cold (unheated) 90% of the time. When I do go out there I have 3 propane torpedo heaters (adjustable from 30,000-60,000 BTU Each), when I crank all of them up to 60k BTU (180k BTU total) they heat my shop up to the point that I can go down to sweat pants and a t-shirt within 15 mins and start turning down their output. Only bad thing is little 20lb propane tanks only last 6-8 hours with these heaters.