May 31, 2022 · And finally, there are car heaters that are plugged into a lighter socket like the RoadPro and can be used as a defroster. 1. Mr. Heater F232000 MH9BX Portable Heater. The heater offers 4,000-9000 BTUs of heat output and warms up to 225 sq ft. It needs to be connected to a propane tank.