I vent outside. Temperatures in Southern Indiana are usually 20 degrees in the winter, but can get down to single digits or below zero. I built my shop, 30' X 50' with gable vents the full length of the sides and to the peak, no roof vent. I insulated the roof rafters and the walls. I also installed a 12' drop ceiling with a 3" gap at one end and various openings for equipment hanging from the ceiling. I installed in floor hot water heat. My hot water heater is gas, with combustion air from outside. So my makeup air is drawn through the gable mixed with the air above my drop ceiling and then into the shop. I can run my DC for hours and maybe get a 2 degree temperature drop. I attribute this to the in floor heat where everything contains heat and the fact that my makeup air is mixed with outside air and air above my drop ceiling that contains heat that has risen. My previous shop had propane heat with a roof vent and could not afford to heat it full time. Other things were putting the electric outlets in conduit on outside of the walls. I could feel cold air coming from the outlets in my previous shop where the electric was run behind the walls. I also used about 15 cans of instant foam and sealed every opening below 12'. The one unexpected thing is when it is sunny out I get about a 5 degree or more temperature increase above my heat set point. So my heater doesn't really run during the day.
When working I had more money than time. In retirement I have more time than money. Love the time, miss the money.