Using a window unit for outage cooling

A window AC can cool one room during an outage when the generator covers its startup load and the cord is rated for the unit. Run the generator outdoors at least 20 feet from openings; never feed it through a wall outlet.

Why a window unit works for outage cooling

A single-zone window air conditioner draws far less power than central air conditioning, which makes it realistic to run on a portable generator or battery backup during an outage. The Building America Solution Center notes that plug-in window units for whole-room cooling typically draw in the range of about 50 to 500 watts, though startup amperage is what actually limits which generator can run it — small generators can only handle so much startup load. Creating one cooled “zone” rather than trying to cool the whole house is also the strategy the guide recommends, since it reduces both the cooling load and the size of backup power you need.

Matching the unit to your generator

Before you buy or plan around a specific window unit, check its nameplate for running watts and starting (surge) watts, then compare that to your generator’s rated output. The Solution Center emphasizes that an emergency cooling system must be sized within the capacity limits of the backup power system, since undersized generators can stall or trip when a compressor starts up. This is a homeowner-level check you can do yourself by reading labels — no electrical work is required to compare numbers on two spec sheets.

What to check

Where the work moves from observation to hands-on risk is generator placement and wiring. Federal guidance is consistent and specific on this point:

• Run the generator outdoors only, at least 20 feet from windows, doors, and attached garages, never in a garage, basement, or crawlspace even with the door open, according to FEMA and Ready.gov.
• Connect the window unit to the generator with a heavy-duty extension cord rated for outdoor use, not by plugging the generator into a wall outlet, per the same FEMA guidance.
• Keep the generator dry; a wet generator or wet cords can shock anyone who touches them, as FEMA notes.
• Let the generator cool before refueling, since spilled fuel on hot engine parts can ignite, per Ready.gov.

If you ever want the window unit’s circuit — or any other circuit — to draw power through your home’s wiring rather than an extension cord, that requires a transfer switch installed by a qualified electrician. FEMA warns that backfeeding a generator into household wiring without a transfer switch can send power out to utility lines and injure or kill a lineman working to restore service, in addition to bypassing your home’s circuit protection.

Protecting people and food during the outage

While the window unit runs, install battery-powered carbon monoxide alarms on every level of the home, since generator exhaust is colorless and odorless and can be fatal even outdoors near windows, according to Ready.gov. Keep refrigerator and freezer doors closed — a full freezer holds temperature for about 48 hours and a refrigerator for about four hours — and discard food exposed to 40°F or higher for two hours or more, per Ready.gov’s food safety guidance. If the outage coincides with extreme heat and your setup can’t keep the room safely cool, Ready.gov recommends moving to a community cooling location rather than waiting it out.

For a broader look at sizing and running a whole backup power plan, see the generators section.

Sources

1. Power Outages | Ready.gov, accessed 8/12/2026
2. Use Generators Safely at Home | FEMA.gov, accessed 8/12/2026
3. Emergency Air Conditioning and Food Refrigeration | Building America Solution Center, accessed 8/12/2026

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