I’m currently using a Mr Heat dual burner on propane. The garage is insulated and the door is insulated as well I crack the side door and garage doors about an inch. I can get it to about 65-70’F. I’m mostly doing engine work or milling and turning metals. Befor doing engine assembly work in my environment I need to do a floor scrub and walls vacuumed to keep the Craptonite out of a new engine. The heater makes it nice so the tools don’t stick to your fingers.