I have a propane unit hanging in one corner of my shop. With the acoustical ceiling, and 6" of insulation I put overhead the propane unit will heat it up pretty dang fast. At least to where its comfortable. I used just over a 100 bucks of propane last year but I don't work all day everyday in the shop either. I also have a round kero heater to use in the house if we lose all power. In the dead of winter I sometime light it once the shop is heated up just to keep it toasted and not run the propane. The unit is pretty efficient and clean burning.
