Recommended size: 5,000–7,500W
A 5,000–7,500W generator runs most window air conditioners reliably. A 5,000 BTU unit draws about 500W running and 1,500W starting, while a 12,000 BTU unit draws up to 1,500W running and 3,000W starting. A medium-tier generator handles the AC plus your fridge, lights, and electronics.
Affordable dual fuel option with CO Alert safety shutoff and MX2 power boost technology. Runs on gas or propane for flexible fuel options during outages.
Window air conditioners are one of the most power-hungry appliances people want to run during an outage, and their wattage varies dramatically by size. A small 5,000 BTU bedroom unit is manageable on a large portable inverter, but a 12,000 BTU unit that cools a living room pulls 1,500W running and up to 3,000W on startup. The safe approach is pairing your window AC with a 5,000–7,500W generator so you have headroom for other essentials running simultaneously. Dual fuel models are ideal here because air conditioning burns through fuel quickly at sustained load, and propane gives you a backup fuel source when gas is scarce. Always plug the AC in first and let the compressor start before adding other loads.
The BTU rating of your window AC directly determines its wattage draw. A 5,000 BTU unit (small bedroom) draws 450–550W running and 1,200–1,500W starting. An 8,000 BTU unit (large bedroom) draws 700–900W running and 2,000–2,500W starting. A 10,000–12,000 BTU unit (living room) draws 1,200–1,500W running and 2,500–3,000W starting. A 15,000 BTU unit (large room) draws 1,500–1,800W running and 3,000–3,600W starting. Check your AC's nameplate for exact amp draw and multiply by 120V for running watts. Starting watts are typically 2–3 times the running watts for AC compressors.
During a summer outage, you likely want the AC, refrigerator, some lights, and phone chargers all running at once. A 10,000 BTU window AC at 1,200W running plus a fridge at 150W plus lights at 200W plus electronics at 100W totals about 1,650W running. The AC startup surge pushes the peak to around 3,800W. A 5,000W generator covers this with margin. If you have a larger AC unit or want to run a microwave occasionally, step up to 7,500W. The key is never starting two motor-driven appliances simultaneously — stagger them 30 seconds apart so their startup surges do not stack.
For a 5,000 BTU window AC, a 3,500W generator works if the AC is your primary load. For 8,000–10,000 BTU, a 5,000W generator gives you safe headroom. For 12,000–15,000 BTU, go with 7,500W to handle the startup surge plus other loads. If you need to run two window AC units (upstairs and downstairs), you need at least 7,500W and should stagger their startups by turning one on, waiting a minute, then turning on the second. Central AC is a different category entirely and requires a 10,000W+ generator or a standby unit.
It depends on the AC's BTU rating. A 5,000 BTU unit needs at least a 2,000W generator (dedicated) or 3,500W (with other loads). An 8,000–12,000 BTU unit needs 5,000–7,500W. Check the nameplate on your AC for exact wattage and size your generator to handle 2–3 times the running watts for startup surge.
Only a very small 5,000 BTU window AC, and only if it is the sole load on the generator. The startup surge of even a small AC (1,200–1,500W) leaves almost no headroom on a 2,000W unit. For reliable operation with other appliances, you need at least 3,500W for a small AC or 5,000W+ for a standard unit.
Running a window AC puts a generator at roughly 50–75% load. At that level, a 5,000W generator burns about 0.4–0.6 gallons per hour, giving you 6–10 hours on a full tank. A 7,500W generator at 50% load uses around 0.6 gallons per hour. Dual fuel models can switch to propane for longer runtime from a 20 lb tank.
An inverter generator produces cleaner power that is better for the AC's electronics, but most window AC units run fine on a conventional generator. The bigger consideration is wattage capacity. Inverter generators in the 5,000W+ range are significantly more expensive than conventional models with the same output. For a window AC, a conventional dual fuel generator is the practical choice.
DuroMax
Affordable dual fuel option with CO Alert safety shutoff and MX2 power boost technology. Runs on gas or propane for flexible fuel options during outages.
Westinghouse
Dual fuel flexibility with CO sensor safety shutoff. Transfer-switch ready with remote electric start and 6.6-gallon tank.
Generac
Powers most essential home circuits during an outage. Electric start and dual fuel flexibility from a trusted brand.
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