I'd put it outside in a metal box and duct the heat from the box back inside. Leave the open end for feeding it outside the box, you'll love it. No smoke inside the shop. Put a blower fan inside the shop blowing to the heated box and duct it back in. If It's on a Thermostat, you can add a damper solenoid to the fire box so when it doesn't call for heat it chokes the fire down.