Generac generators are designed to run on one fuel source, which is natural gas. However, they can also run on liquid propane (LP) . Generac home backup generators are designed to automatically sense a power outage and turn on, delivering backup power to your home. They will run until utility power returns, whether thats two hours or two weeks. 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.