Usage and Safety 
generator size

Get the right-sized generator for your needs.
Selecting the proper wattage of an electric generator involves more than simply adding up the wattage of the lights and appliances you want to power. Electric motors require extra power to start up. A sump pump, for example, may need more than 1,200 watts of power to start up, but only 800 or so to run afterwards. A furnace fan may need over 2,000 watts to start running, then drop to half that level. Light bulbs, water heaters, radios and other motorless end uses have the same wattage requirements to start as to run.

Some generators provide a few hundred watts of power, which severely limits what you can operate with them. Planning to run just a few large appliances or tools and some lights may require from 4,000 to 12,000 watts' total power from your generator, or more. Smaller generators cost less to buy, but may not meet your needs.

Tip: Careful practice involves making sure that electrical devices are turned off before you connect them to a generator or generator-powered circuit. Once the generator is running, switch devices on one by one. Shut them down again before switching back to your utility service.

Always refer to manufacturer's technical information to ensure your generator performs safely and properly.