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Short answer: a typical 5,000 to 8,000 BTU window air conditioner draws 450 to 750 watts running and surges to 1,500 to 2,500 watts when the compressor starts, so a 2,200-watt inverter generator can run a small unit by itself and a 3,500-watt generator runs an 8,000 BTU unit with the fridge and lights. Larger 10,000 to 15,000 BTU units need 4,000 watts or more. A 2kWh power station runs a 6,000 BTU unit for about 3 hours of continuous cooling, or 6 to 8 hours with the compressor cycling in a closed room overnight. A soft-start kit cuts the surge by 60 to 70 percent and lets smaller generators and batteries handle bigger AC units.
Window AC Power Draw by Size
| AC Size | Cooling Area | Running Watts | Starting Surge (no soft start) | Surge with Soft Start |
|---|---|---|---|---|
| 5,000 BTU | 150 sq ft | 400-500W | 1,200-1,800W | ~600W |
| 6,000 BTU | 250 sq ft | 500-600W | 1,500-2,000W | ~700W |
| 8,000 BTU | 350 sq ft | 650-750W | 1,800-2,500W | ~900W |
| 10,000 BTU | 450 sq ft | 850-1,000W | 2,200-3,000W | ~1,100W |
| 12,000 BTU | 550 sq ft | 1,000-1,200W | 2,800-3,600W | ~1,400W |
| 15,000 BTU | 700 sq ft | 1,300-1,500W | 3,500-4,500W | ~1,700W |
Newer inverter-compressor window units (increasingly common since 2022) ramp up gradually instead of surging and can draw 30 to 40 percent less power at partial load. If you are buying a window AC specifically for outage use, an inverter model is the one to get; it makes the whole generator or battery question easier.
What Size Generator You Need
| What You Want to Run | Minimum Generator (rated watts) | Comfortable |
|---|---|---|
| One 5,000-6,000 BTU AC alone | 1,800W inverter | 2,200W |
| 6,000 BTU AC + fridge + lights + fan | 2,500W | 3,500W |
| 8,000 BTU AC + fridge + lights + Wi-Fi | 3,000W | 3,500-4,500W |
| 10,000-12,000 BTU AC + essentials | 4,000W | 5,500W |
| Two window units + essentials | 5,500W | 7,500W |
| 15,000 BTU (often 240V) + essentials | 5,500W with 240V | 7,500W |
The surge is what trips people up. A generator’s peak rating covers a surge for a few seconds, which is enough for a compressor start, but only if nothing else is surging at the same time. Start the AC first, alone, then add the fridge and other loads. Our roundup of the best inverter generators for home backup lists surge ratings for each unit, and the generator size calculator will add an AC to the rest of your list.
The Soft-Start Kit: The Upgrade That Changes the Math
A soft-start kit is a small module wired into the AC’s compressor circuit that ramps the motor up over a fraction of a second instead of slamming it on. It cuts the starting surge by 60 to 70 percent. An 8,000 BTU unit that surged to 2,300 watts now surges to about 900, which means a 2,200-watt inverter generator or a 1,800-watt power station can start it. RV owners have used these for years; they work on window units too. Installation is a 20-minute job for anyone comfortable with a screwdriver and a wiring diagram, or a quick job for an HVAC tech. Some soft-start kits are plug-in style and need no wiring at all for smaller window units.
Check the current price of soft-start kits for air conditioners on Amazon
Running a Window AC on a Portable Power Station
Runtime = battery watt-hours × 0.85 ÷ average draw. The key word is average: in a closed, shaded room at night, the compressor cycles on about 40 to 60 percent of the time, so a 600-watt AC averages 300 to 360 watts.
| Power Station Size | 6,000 BTU, continuous (600W) | 6,000 BTU, cycling at night (~330W) | 8,000 BTU, cycling (~420W) |
|---|---|---|---|
| 1,000Wh | ~1.4 hours | ~2.6 hours | ~2 hours |
| 2,000Wh | ~2.8 hours | ~5.2 hours | ~4 hours |
| 4,000Wh | ~5.7 hours | ~10 hours | ~8 hours |
| 6,000Wh | ~8.5 hours | ~15 hours | ~12 hours |
The practical reading: a 2kWh unit gets one bedroom through a summer night with a 6,000 BTU unit and the door closed. A 4kWh unit does it comfortably and still runs the fridge. Confirm the station’s surge rating exceeds the AC’s start (or add a soft-start kit), and use the unit’s UPS mode so the AC does not restart abruptly if you switch sources. Our guide to the best portable power stations for home backup lists surge figures by model; the EcoFlow Delta 2 Max and Delta Pro 3 are two units that handle AC starts well.
Check the current price of 2,000Wh power stations with 2,400W output on Amazon
Solar panels extend this in a real way. A 400-watt panel array in summer sun produces about 2kWh a day, which nearly covers the overnight AC use of a 2kWh station. See best solar panels for portable power stations.
Making the Cold Go Further
- Cool one room, not the house. Close the door and blinds. A 6,000 BTU unit that struggles with an open floor plan holds a closed bedroom in the low 70s.
- Run it in the evening and overnight. Outdoor temperatures drop, the compressor cycles less, and sleeping in a cool room matters more than a cool afternoon.
- Set it to 76 to 78°F. Every degree colder adds roughly 3 to 5 percent to the run time.
- Use the fan-only mode during the day on a battery. A fan draws 50 watts; the compressor draws 600.
- Block the sun. Foil or a reflective shade on a sun-facing window cuts heat gain dramatically.
- Clean the filter. A clogged filter raises draw and lowers cooling.
Worked Example: One Bedroom Through a Summer Night
A family in Houston loses power at 6 pm in August with an outdoor temperature of 94°F. They have a 6,000 BTU window unit in the main bedroom, a 2,048Wh power station rated for 2,400 watts continuous and 4,800 watts surge, and a 3,500-watt inverter generator.
- 6 to 9 pm: generator runs outside, feeding the AC (600W), the refrigerator (150W average), a fan, and phone chargers through 12-gauge cords. The power station charges from the generator at the same time. Fuel used: about 0.7 gallons.
- 9 pm: generator shut off for the neighbors. The AC, now in a closed bedroom with blinds drawn, moves to the power station. Room is already at 74°F, so the compressor cycles about half the time, averaging 330 watts.
- 9 pm to 3 am: the power station delivers roughly 2,048 × 0.85 ÷ 330 = 5.3 hours. Around 2:30 am it hits 10 percent and the AC stops. The room drifts from 74 to about 79°F by 6 am with the door closed, which is uncomfortable but safe.
- 6 am: generator restarts, AC and fridge back on generator power, battery recharges for the next night.
With a 4kWh station, the AC runs until morning. With a soft-start kit and an inverter-compressor AC, the same 2kWh battery would likely make it to sunrise. This is the kind of arithmetic worth doing in July, not during the outage.
Safety and Setup Notes
- The generator sits outside, 20 feet from the house, exhaust away from the AC’s outdoor side (which pulls in outdoor air). Read generator carbon monoxide safety.
- Use a 12-gauge outdoor extension cord for the AC. A thin cord drops voltage under the compressor’s load and can cause the unit to trip or overheat.
- Plug the AC directly into the cord, never through a power strip or a light-duty surge protector.
- Older window units and conventional generators together can cause a buzzing compressor from dirty power. An inverter generator solves it; see inverter vs conventional generators.
- If the AC will not start and the generator is big enough on paper, the surge is the issue. Start the AC before anything else, or add a soft-start kit.
Heat is dangerous for infants, older adults, and anyone with heart or lung conditions. If someone in the house is in that group, cooling one room during a summer outage is not a comfort item; our checklist for a power outage with a baby or elderly parent at home treats it as the priority it is.
Frequently Asked Questions
Will a 2,000-watt generator run a window air conditioner?
A 5,000 to 6,000 BTU unit, yes, started first and alone. An 8,000 BTU unit usually needs a soft-start kit or a 3,000-watt-plus generator because of the starting surge.
How long will a power station run a window AC?
A 2kWh unit runs a 6,000 BTU AC for about 3 hours continuously or 5 to 6 hours with the compressor cycling overnight in a closed room. A 4kWh unit roughly doubles that.
Can I run an AC and a refrigerator on the same generator?
Yes, on 3,500 watts or more. Start the AC first, wait for it to settle, then plug in the fridge so the two compressors do not surge at once.
What is a soft-start kit and do I need one?
A module that ramps up the compressor gradually, cutting starting surge by 60 to 70 percent. If your generator or battery is marginal for your AC’s size, it is the cheapest fix.
Is a portable AC easier to run on a generator than a window unit?
No. Portable (rolling) AC units are less efficient and draw more watts for the same cooling, and single-hose designs pull hot air into the room. A window unit is the better outage choice.