The PH51W water heater is available in 12volt and 24volt and designed to be used as auxiliary engine heaters for trucks, RVs, boats, construction and farm equipment. In extreme cold temperatures, the heaters will keep the engine warm and also eliminate cold engine starting problems without the necessity of engines idling or frequent startups. In addition, the heater will provide heat to keep the operator cabin or sleeper berth warm and comfortable for a fraction of the cost in comparison to engine idling. The PH51W has a internal water pump compared to the PH53W which has a external water pump and is available in 12v.