To size a home generator, begin by adding the wattage of all the appliances that are likely to be running at the same time, including the start-up loads. The generator's output needs to be at least slightly larger than this number.
Many generator manufacturers have online sizing calculators to help simplify the sizing process. Consumers can put the size of their house in, and then choose their appliances from a list. The calculator uses this information to estimate wattage needs based on typical requirements. This also factors in the start-up loads that occur when a new appliance turns on, which can be three to five times larger than the typical running rate. Start-up loads can overload generators if not taken into account.
People with special power needs or who are buying for a large home may also want to speak to a generator expert. Most generator manufacturers have experienced sales representatives who can help match the right generator with the right person. While some people think bigger is better, large generators also have their drawbacks.
Larger generators are more expensive and may create more noise while they are running. This can be annoying even with emergency generators because they have to be turned on regularly between power outages to ensure they are working properly. The smallest generator that is powerful enough to handle the load is the best choice for most situations.