What is a standby generator?
A standby generator is one that is always connected to your home. It looks and acts a bit like a central air conditioner. The standby generator runs on an engine that can be powered by gasoline, natural gas or propane. There is an automatic transfer switch that switches power from your normal household electricity to the generator during a power loss and switches back when power is restored.
How much propane?
The amount of propane used depends on the amount of electricity used, or the load that is put on the generator. The cost also depends on the efficiency of the generator and its limits. For a moderate house, on some generators you might expect to use a gallon or more for an hour of propane use. There are a lot of variables, and to get a realistic estimate you'll need an installer to quote you an estimate based on what you will have installed and your specific needs.