Abstract: A backup power supply includes a housing with a central compartment holding an electrical generator preferably an alternator and a hydrocarbon powered motor. The housing further includes first and second side compartments. The first side compartment stores the electronic components of the generator. A top covers all three compartments and has two side overhangs and a forward overhang. The side overhangs provide air inlets to the two side compartments which in turn permit passage of air into the central compartment. The forward overhang includes an air outlet which allows air to be directed from the central compartment to outside the housing. The alternator itself includes a fan which pulls air from one side compartment into the central compartment. The motor has a second fan that pulls air into the central compartment from the second side compartment. Further the exhaust from the motor is encased in a shroud which leads directly to a passage through the top to the forward outside opening.