When a heat wave knocks out the power, staying cool stops being about comfort, especially for older people, young kids and anyone with a medical condition. A portable power station can help, as long as you go in with realistic expectations.
Will it start the AC?
Window units have compressors, and compressors have a startup surge. You need enough continuous output and enough surge:
| Window AC size | Running watts | Starting watts | Minimum power station output |
|---|---|---|---|
| 5,000 BTU | 400–500 W | 1,000–1,500 W | 1,000 W / 1,500 W surge |
| 8,000 BTU | 650–750 W | 1,600–2,200 W | 1,500 W / 2,200 W surge |
| 10,000 BTU | 850–1,000 W | 2,000–2,800 W | 1,800 W / 3,000 W surge |
| 12,000 BTU | 1,000–1,200 W | 2,500–3,500 W | 2,400 W / 3,600 W surge |
Most power stations in the 1,800 W class can start an 8,000 BTU unit. Portable ACs with a hose usually use 10–20% more than a window unit with the same BTU rating.
How long will it run?
Once the room cools down, the compressor cycles, but during a heat wave it runs most of the time. Plan on it running 70–90% of the time.
Runtime ≈ battery Wh × 0.85 ÷ (AC running watts × share of time it runs)
For an 8,000 BTU unit (700 W) running 80% of the time:
| Power station | Approx. runtime |
|---|---|
| 1,000 Wh | ~1.5 hours |
| 2,000 Wh | ~3 hours |
| 3,600 Wh | ~5.5 hours |
| 6,000 Wh (expanded) | ~9 hours |
You can run your own numbers in the runtime calculator.
Ways to make the cooling last
- Cool one small room. A bedroom with the door shut needs far less run time than an open-plan living area.
- Cool the house down before a forecast outage, and keep the blinds closed on the sunny side.
- Run the AC in bursts to drop the temperature a few degrees, then switch to a fan (50–60 W) for a few hours.
- Set it to 78–80°F rather than 70°F. Every degree helps.
- If you’re buying an AC anyway, get an inverter model. Variable-speed units start gently and can idle at 200–400 W.
- Fit a soft-start device to a regular unit. It cuts the surge by 50–70%, so a smaller power station can start it.
- Add solar. The need for AC peaks exactly when the sun is strongest.
Fans first
For a lot of outages, a few box fans or USB fans and some cold water are enough, and they’ll run all day on a mid-size power station. Save the AC for the hottest hours, or for the people in the house who need it most.
If it climbs above the mid-80s °F indoors and you can’t cool down, head to a public cooling center. Heat illness can turn into an emergency quickly, especially for seniors and people with heart conditions.
Is it worth it?
A power station can run a window AC, but battery size limits you to a few hours unless you have 3,600 Wh or more, or solar. For cooling all night through a long outage, you’ll want an expandable home battery or a generator.