Generac home backup generators are designed to run on one fuel source, either natural gas or liquid propane (LP) fuel. They are factory set to run on natural gas, but can be configured to run on LP at the time of installation. Generac generators are engineered to run for long periods of time required during a severe power outage or on a job site, utilizing the same type of pressurized oil lubrication used to give automobile engines long and trouble-free lives. The generators are installed outside, just like an air conditioning unit, and wait for the signal to kick into gear when the power goes out. Once the generator senses a power outage, it turns on automatically and delivers backup power to the home. The generator will run until utility power returns, whether thats two hours or two weeks.