Understanding the Power Requirements
Window air conditioners are one of the most generator-challenging appliances because of the large gap between running and starting watts. A 10,000 BTU window AC runs on about 1,200 watts but needs 3,600 watts to start the compressor motor. If your generator can't handle that startup surge, the AC won't start — or worse, it will trip the generator's overload protection repeatedly.
Window AC wattage scales with BTU rating. A 5,000 BTU unit uses roughly 450W running and 1,350W surge. A 10,000 BTU unit uses 900–1,200W running and 2,700–3,600W surge. A 15,000 BTU unit uses 1,400–1,700W running and 4,200–5,100W surge. Always check your specific unit's nameplate — EER (Energy Efficiency Ratio) varies significantly between models and affects actual wattage.
Choosing the Right Generator Size
For a single 10,000 BTU window AC unit, a 4,000-watt generator is the minimum and a 5,000-watt unit is recommended to leave headroom for the refrigerator, lights, and other essentials. A soft-start kit (MicroAir EasyStart, ~$200) reduces the AC startup surge by 50–70%, potentially allowing a 3,000-watt generator to run a 10,000 BTU unit.
This appliance surges to 3.6 kW (3× running watts) at startup. Your generator's starting watts — not rated watts — must exceed this. Always verify the generator's peak/surge rating before purchasing.
Wattage Summary
| Specification | Value |
|---|---|
| Running Watts | 1.2 kW |
| Surge Watts | 3.6 kW |
| Minimum Generator | 4 kW |
| Recommended Generator | 5 kW |
Buying Tips
Look at your AC nameplate for 'Running Amps' and multiply by 120 (or 240 for 240V units) to get running watts.
EER rating matters: a 12 EER unit uses 17% less power than a 10 EER unit at the same BTU. Higher EER = smaller generator needed.
Soft-start kits ($150–$250) dramatically reduce surge requirements and are well worth the cost if you have a smaller generator.
Modern inverter-type window ACs (Midea U-shaped, LG Dual Inverter) have much lower starting surges — easier on generators.
What Else Can Run With It?
Common appliances paired with this load. Combined running load: 1.6 kW. Recommended generator for this combo: 5 kW.
| Appliance | Running Watts |
|---|---|
| Window Air Conditioner ← this page | 1200W |
| Refrigerator | 150W |
| LED Lights (10) | 100W |
| TV | 120W |
| Phone Chargers | 50W |
| Combined Running Total | 1.6 kW |
* Recommended generator for this combination: 5 kW (includes 20% safety margin and surge headroom)