Thanks for the reply. The walls and celiing are insulated to code...what exactly that is Im not sure but I will find out. The double door and single stall door I have insulated personally with foil backed styrofoam which has helped to the tune of maintaining 35-40 degrees even when the temps dip...
I have a 3 stall garage in southeastern Minnesota so it goes without saying that it can get very cold and stay there for weeks at a time. I have a trusted professional who will be installing the gas line due to come in the next week. Throughout our conversation on which size heater to buy in his...