I have an Envirofire EF2 in my insulated pole barn shop that is approximately the same size as the shop you are planning. It will run me out of the shop on the coldest days if run on more than medium heat. I will burn a full bag of pellets on a cold day, run the stove on high for the first hour and then turn it down for the rest of the day. Turn it off at night, and the shop stays well above freezing in our coldest weather. Mine is a through wall installation done by a professional, 18 inches off the floor to comply with our local fire code for potential of gasoline fumes from a project drifting across the floor, done with a permit and inspected to comply with code and to satisfy my fire insurance carrier. I am near Silverton, Oregon, temperature drops to the 20's in the dead of winter, but most often in the 30's during the heating season. Insulation is 6 inch fiberglass in the walls, 2 inch drape under the steel roof, with 6 inch below that. Floor is 6 inch fiber reinforced slab, and the floor to wall union is sealed with closed cell fire resistant spray foam from Lowes.
I was going to burn wood, but my farm fire insurance carrier would not approve that installation.
Very happy with the installation. Had propane in my other shop and would blow through $50 a day worth of propane in a day, had the unit cycling on and off all day long and wavered from too cold to too hot with every cycle. The pellet stove burns a $3 bag of pellets a day, is quiet and does not cycle between hot and cold all day long. Also makes a hot spot for friends that drop by out of the cold rain, to sit and warm up, drink coffee, and shoot the breeze.
I have used the Canadian built Enviro stoves for 18 years, purchased one timing module in all that time, just use my shop vac and vacuum it out when it is stone cold once a year, and oil the motors once a year. The tray under the burn pot is emptied after a ton of pellets is burned, and the burn pot is scraped with the tool once a week. This stove was removed from the house after being used as a primary heat source for 18 years, and has the auto-start feature. A pellet stove must be run on high for 45 minutes every day to get the heat exchanger hot enough to blow the fines out the exhaust vent, and a vertical chimney has to be swept out after a season of heating. The horizontal direct vent clears itself and I have yet to have any soot build up in it.
I did install a ceiling fan 12 feet out from the stove, and at the bottom of one truss, hooked the power to my lighting circuit so it turns off with the lights. Run it on low and it forces the hot air down and circulates it throughout the entire shop. Without the fan the heat goes up and stays there.
