Emergency diesel generators in outdoor enclosures use large amounts of electric resistance heat to keep the engines warm all year. The heat is delivered to the jacket water of the engine by means of an electric resistance cartridge heater. For mid sized generators (150 KW – 1,000 KW) the annual electric use to deliver 130 degree F water can be 10,000 to 30,000 kwhr in a climate zone with 4,000 heating degree days (65 F base). An alternative to electric heating of the jacket water, is to solar heat the enclosure with 110 F air. This reduces the heat loss from the engine and therefore reduces the demand on the electric resistance heater. The paper describes the opportunity for solar air heating of emergency generators and the design and construction of two ground mounted systems and one solar heating building at the US Geological Survey in Reston, VA.