Before buying any generator, you should determine the power requirements of your home and your most essential large electric appliances. Refrigerators, air conditioning, sump or well pumps, medical devices, electric water heaters and portable space heaters will likely have the highest power draw and be most essential during power outages. Many generator manufacturers have online wattage calculators to help you determine what size generator is the best fit for your home.
You can also calculate this number yourself by finding the wattage rating label on each of your essential appliances. Many appliances will be labeled with “Starting Watts” and “Running Watts”, the former is the power-draw when the appliance first turns on, while the latter is the draw once it’s running.
If the Starting Watts are not listed you can usually multiply the Running Watts by three. Add up the Starting Watts for each appliance and multiply the total by 1.5 to create a margin of safety. A small to medium size U.S. household averages a minimum of 5,000 to 7,500 watts, so many generators are sold with 7,500 to 10,000 watt outputs. Note: Some generators are listed by watt (W) and some by kilowatt (kW). A kilowatt is 1000 watts.