When purchasing a generator, the most important determination is the power requirements of your house and especially your large-draw electric appliances. Refrigerators, air conditioning, sump pumps, water heaters and space heaters will have some of the highest power draw in your house. Online wattage calculators will help you find what size generator is the best fit for powering your whole house.
You can also calculate this yourself by finding the wattage rating label on each of your electrical appliances. You should multiply the total watts of your appliances by at least 1.5 to create an adequate margin of safety. You can also check with your power company or on your electric bill to find your regular power needs.
In general a small to medium size U.S. house averages a minimum of 5,000 to 7,000 watts so many standby generators are sold with a minimum of 8,500 to 10,000 watt outputs. NOTE: Some generators are listed by watt (W) and some by kilowatt (kW). A kilowatt is 1000 watts. An air-cooled generator uses the surrounding air to cool the engine. This could be done passively by the surrounding air absorbing the heat and rising away from the generator, or this could be accomplished with “forced air cooling” which uses a fan to blow air across the generator’s engine.