A standby generator is for use during a power outage…whether the outage lasts two hours, two days or two weeks. Standby means that it is basically sitting there, waiting until it’s needed. It senses the power outage and turns on automatically, whether you’re there or not. The size generator you need depends on what you want to power during the outage. You can power just a few things, like the furnace, some lights and the refrigerator (basically the essentials) or you can have a larger size that will power the entire house. Of course there are also sizes in-between.