How to Calculate Generator Sizing
- 1). Make a list of start-up and running wattages needed for all the household lighting and electrical devices you will use during a power outage. Most tools, appliances and other electrical devices have the wattage requirements listed in the user manual or printed on a specification plate attached to the unit. Don't forget to add sound systems, computers and TV power requirements to your list.
- 2). Write down the start-up wattage and ignore running wattage on devices with a motor or compressor, such as refrigerators, vacuum cleaners and air conditioners. Motors require as much as three times more power during start-up.
- 3). Total all the wattages listed. Add 20 percent to this figure to avoid accidentally overloading your generator and to allow for any other small appliances you may add in the future.
- 4). Select a standby generator with a rated output as close to your final figure as possible.
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