What Size Backup Generator—Standby Generators Sizing Guide
Look at the main breaker in your service panel. The majority of modern homes have a main breaker rated at 100, 150, or 200 amperes. In most cases, the main breaker represents more than double what the home actually uses.
Consider an air-cooled 22-kilowatt generator capable of supplying 86 amperes of power while running on natural gas. With the management capability of your automatic transfer switch, it’s very likely this is all the power you will ever need. A pair of three-ton air conditioners will total about 38 amps of current if both run at once, leaving you another 48 for the rest of the house.
That is enough to power a refrigerator, freezer, sump pump, half a dozen incandescent lights, and your television with power to spare. You can still surf the internet on your computer, charge your cell phones and other electronics, and keep the alarm system powered.
Use the following sizing calculator for a ballpark estimate of your power needs. Actual appliances have differing power requirements and may need more or less. This sizing calculator helps estimate the general size required to give you a good starting point on your research.
Tip: If you have two A/C units of the same size, check the requirements of one first, then double the power required and add it to the total.
Sizing Guide Calculator Here
Tip: Don’t buy just enough or too much. The right generator has enough power to handle the things you want it to power with some margin, but isn’t so large that it uses more fuel than necessary. Determine what it should power during an outage, then add about 30 percent to the total kilowatts and buy a generator in that range.
Air-Cooled Home Standby Generators
Air-cooled Backup Generators can power everything or just the essentials. Manufacturers often bundle 8 to 12 kilowatt models with an automatic transfer switch load center. These have room for a limited number of circuits and don’t include any power management features. When the power goes out, only the circuits connected to the load center will have electrical power from the standby generator.
Models with 12 to 22 kilowatts of power can provide more power for more appliances. Look for automatic transfer switches that control power to the entire home. They include sophisticated power management capabilities that allow you to power multiple 240-volt appliances such as central air conditioners.
Liquid-Cooled Home Standby Generators
As homes get larger and use more power, the standby generator capacity required also increases. Homes with 300 or 400 ampere service are going to struggle with an air-cooled generator. Liquid-cooled natural gas models can supply even the largest luxury homes. The basic principles remain the same however. Add up all the power requirements and choose a generator that can supply at least 30 percent more power.