To size a generator properly for a home, owners should determine the essential appliances and the wattage required to run them. They should multiply the sum by 1.5 to allow for start-up wattage of the appliances and purchase a generator able to provide the necessary power.
Generators are available in two different styles. Portable generators have wheels to roll them to a location outside the house for operation. Permanent generators remain in one location. Permanent generators are usually more expensive than portable units, but provide more power. In addition, they operate on natural gas, propane or diesel fuel while portable units often operate on gasoline.
Safely operating a portable generator often involves starting the unit manually, running a heavy-duty extension cord into the home, and plugging appliances into the outlet. Electricians often hard-wire permanent generators into the home's electrical system. These systems automatically disconnect the home from the power grid and start the generator when an outage occurs.
When sizing a generator, most homeowners ignore high-energy use appliances that they do not need during the emergency. Most people are able to live without an oven or air conditioner for several hours. Planning to operate these appliances on a generator requires a much larger unit, which adds to the installation cost.