Central AC Generator Sizing: What You Need

Running watts and starting watts for central AC

Central air conditioners have two power figures that matter when you compare generators: running watts and starting watts. Running watts, sometimes called rated watts, are the power the AC needs to keep running after it is on. Starting watts, also called surge watts, are the extra power the compressor needs for a moment when it starts. A generator listing states both figures, and the starting figure is usually the larger one.

The U.S. Energy Information Administration explains that electricity is measured in watts, a unit of power. A watt is a small amount of power; some devices need only a few watts, while others need thousands. For a central AC, the running watts are what the unit draws during normal operation, and the starting watts cover the initial surge.

When you read a generator title, the first watt figure is often the starting watts, and the second is the running watts. For example, a title that says "7,500 starting watts, 6,000 running watts" means the generator can briefly supply 7,500 watts to start a motor and then 6,000 watts continuously. The same logic applies to power stations, but they state continuous output and peak output instead.

• Running watts: the power needed to keep the AC operating.
• Starting watts: the extra power needed to start the compressor.
• Generator titles list both figures; the starting figure is usually first.
• Power stations list continuous output and peak output.

Read the AC label for the electrical ratings

To find the running and starting watts for your central AC, look at the nameplate on the outdoor condensing unit. The label lists electrical ratings such as volts, amps, and sometimes watts. The running watts can be estimated by multiplying volts by amps, but the label may state the wattage directly. The starting watts are not always on the label; they are often higher than the running watts and may be listed in the manufacturer's specifications.

This site does not size a home or tell you which generator will run your AC. The appliance label and the manufacturer's documentation are the only sources for your AC's exact figures. If the label is hard to read or missing, contact the manufacturer or a licensed electrician.

The Florida Division of Emergency Management advises checking and testing your generator before a storm and reading the manual. That guidance applies to the generator, not to the AC. For the AC, the label and the manufacturer's page are the starting point.

Compare the figures with generator listings

Once you have the running and starting watts for your AC, compare them with the generator's stated figures. The generator's running watts must be at least the AC's running watts, and the starting watts must be at least the AC's starting watts. If either figure is lower, the generator may not start or run the AC.

The same comparison applies to power stations. A power station lists continuous output and peak output. The continuous output is like running watts, and the peak output is like starting watts. However, power stations have a limited capacity measured in watt-hours, which is a different figure from output. The capacity determines how long the station can supply power, not whether it can start the AC.

The site's buying guides compare generators and power stations on stated details, not on measured performance. Use the guides to narrow your options, then read the maker's page for the exact figures.

Why this site does not size a home

This site does not provide a wattage worksheet or an appliance table that sizes a home. Sizing a generator for central AC depends on the specific AC model, the age of the unit, and other loads in the home. Only the appliance label and the manufacturer's specifications can give you the correct figures.

A licensed electrician can help you determine the total load for your home and whether a generator or a transfer switch is appropriate. The local permit office and the maker's manual also decide how a generator connects to your home's wiring. This site does not give wiring or connection advice.

For storm preparation, the Florida Division of Emergency Management recommends checking your generator before the season and reading the manual. The National Weather Service suggests checking emergency equipment such as generators and storm shutters before hurricane season begins. Those steps are about readiness, not about sizing.

What to pick for your situation

If you want to power central AC during an outage, you need a generator with enough running and starting watts. The site's generator guides list models by wattage class, and the power station guides list stations by capacity. Use the figures from your AC label to narrow the options.

For a Florida home with central AC, a larger portable generator or a standby generator may be necessary. The best large portable generators for hurricanes guide covers high-wattage models. If you prefer a standby unit, the best standby generators for Florida homes guide is the starting point.

If you live in an apartment or condo, a power station may be a better fit, but it likely cannot run central AC. The best power station for apartments guide explains the capacity bands. For a house, compare the best backup power for Florida guide to see the full range.

What to pick for your situation

Questions

What are running watts for a central AC?

Running watts are the power the AC needs to keep operating after it starts. The appliance label or the manufacturer's specifications list this figure.

What are starting watts for a central AC?

Starting watts are the extra power the compressor needs for a moment when it starts. They are usually higher than running watts and may not be on the label.

How do I find the watts for my AC?

Read the nameplate on the outdoor condensing unit. It lists volts and amps, and sometimes watts. Multiply volts by amps to estimate running watts, but check the manufacturer's page for exact figures.

Can a power station run central AC?

A power station lists continuous output and peak output, similar to running and starting watts. However, capacity in watt-hours limits how long it can supply power. Compare the figures with your AC's label.

Does this site tell me which generator to buy?

The site compares generators on stated details, not measured performance. Use the guides to narrow options, then read the maker's page for exact figures.