Can a generator run central AC?

A generator may run your central AC, but the answer is not hiding in the AC tonnage or the largest watt number printed on the generator. You need the AC’s running and starting demand, the generator’s continuous and surge ratings, and a list of everything else that will be on when the compressor starts.

Get the four numbers that matter

Photograph the data plates on the outdoor AC unit, indoor air handler, and generator. Then find:

AC running watts or the manufacturer’s running-load data;
AC starting or locked-rotor demand;
generator continuous output on the fuel you will use;
generator surge or motor-start output.

The indoor blower counts too. So do condensate pumps, heat strips, and any other accessory that runs with the system. Tonnage measures cooling capacity; it does not tell you the electrical starting load.

A 7,500-watt generator is not an automatic yes

Suppose a generator is rated for 7,500 continuous watts and 9,500 surge watts. An AC that uses 3,500 watts once running might appear to fit. But if it needs 10,500 watts for a moment at startup, the generator can still stall or trip. If the refrigerator, lights, and a pump are already using 1,500 watts, the running margin is smaller too.

Use the generator and AC calculator to compare documented numbers. If the starting data is missing, the calculator cannot manufacture an honest answer.

Decide what stays on with the AC

Write down the loads that matter during an outage: refrigerator, lights, medical equipment, internet, pumps, and cooking equipment. Ready.gov recommends prioritizing essential loads because backup power may not carry everything at once (Ready.gov).

This is often where a workable plan appears. Cooling one room with a window unit may leave plenty of capacity for food, lights, and medical needs. Central AC may require automatic load shedding or a larger generator.

The connection is part of the answer

A portable generator cannot power central AC through an extension cord. A house connection needs properly selected inlet and transfer equipment that prevents generator power from feeding back onto utility lines. OSHA warns against connecting a portable generator to a building without a properly installed transfer switch (OSHA).

Ask the electrician to put the included loads, excluded loads, transfer equipment, and startup test in writing. A soft starter may reduce starting demand on compatible equipment, but it is not a substitute for the load calculation or the connection design.

Keep the storm plan simple enough to use tired

Portable generators belong outdoors, at least 20 feet from the house, with exhaust pointed away. CPSC also recommends battery-backed carbon-monoxide alarms on every level and outside sleeping areas (CPSC). Never run a generator in a garage, under a house, or near an open door or window.

Do not approach electrical equipment in standing water. Permanent equipment also needs a site plan that accounts for flooding and service access; FEMA recommends locating generators and transfer equipment above the applicable flood-protection elevation where required (FEMA).

The useful final answer is specific: this generator can start this AC, on this fuel, while these other loads are running, through this transfer setup. Anything vaguer is still a guess.

Sources

Ready.gov — Power outage hazard information sheet, accessed 8/12/2026
CPSC — Carbon monoxide information center, accessed 8/12/2026
OSHA — Grounding requirements for portable generators, accessed 8/12/2026
FEMA — Protecting building utility systems from flood damage, accessed 8/12/2026