24 Volt Window Air Conditioner & Heater 9,000 BTU/h (0.75 ton)

Only takes 500 watts to run and operates directly off your 24 volt battery. The absolutely cheapest way to run this would be to wire it to two car batteries in series for 24 volt operation. You can also select a package with battery, solar, or charge controller to have a fully functional self-contained cooling and heating system for total off-grid operations.

9,000 BTU/h window unit heat pump that can operate as an air conditioner and as a heater. This heat pump is 5 times more efficient than using an electric heater. It is at least twice as efficient as a 110 volt window AC unit and effectively three times more efficient when using with an off grid 24 or 48 volt system, without requiring an inverter. All parts inside are DC-native. This is "how it's done", if you are serious about the most efficient and reliable heat pump.