What Size Generator to Run a Window AC Unit?
Last updated:
Fact-checked by Marcus Hayes, Master Electrician (License #CA-EL-89241), 15 years generator installation experience.
Window air conditioners have high starting watt surges because their compressors use induction motors. A 5,000 BTU unit needs 1,500 starting watts, while a 15,000 BTU unit needs 4,500. This guide helps you match the right generator to your window AC size.
Key Takeaways
- A 5,000 BTU window AC needs 500 running watts and 1,500 starting watts — a 2,000W generator is sufficient.
- A 10,000 BTU window AC needs 1,000 running watts and 3,000 starting watts — a 3,500W generator.
- A 15,000 BTU window AC needs 1,500 running watts and 4,500 starting watts — a 5,000W generator.
- AC compressors have 3x starting watt surges — always size for starting watts, not running watts.
- A solar generator can run a window AC but runtime is limited (4-8 hours per 4,000Wh).
Window AC wattage by BTU
A 5,000 BTU window AC uses 500 running watts and 1,500 starting watts. A 10,000 BTU unit uses 1,000
running watts and 3,000 starting watts. A 15,000 BTU unit uses 1,500 running watts and 4,500 starting
watts. Starting watts are 3x running watts because AC compressors use induction motors that need a
large burst of power to start.
| AC Size | Running Watts | Starting Watts | Min. Generator Size |
|---|---|---|---|
| 5,000 BTU | 500W | 1,500W | 2,000W |
| 8,000 BTU | 800W | 2,400W | 3,000W |
| 10,000 BTU | 1,000W | 3,000W | 3,500W |
| 12,000 BTU | 1,200W | 3,600W | 4,000W |
| 15,000 BTU | 1,500W | 4,500W | 5,000W |
Best generators for window AC backup
For a 5,000-8,000 BTU window AC, the Honda EU2200i (2,200W starting) or Westinghouse iGen4500 (4,500W
starting) are the best gas options. For a 10,000-15,000 BTU unit, the Westinghouse iGen5000DFc (5,000W
starting) or DuroMax XP12000EH (12,000W starting) are needed. For indoor-safe battery backup, the
EcoFlow Delta Pro 3 (4,000W, 8,000W surge) handles most window AC units.
Frequently Asked Questions
What size generator do I need to run a window AC unit?
A 5,000 BTU window AC needs 500 running watts and 1,500 starting watts — a 2,000W generator is sufficient. A 10,000 BTU unit needs 1,000 running watts and 3,000 starting watts — a 3,500W generator. A 15,000 BTU unit needs 1,500 running watts and 4,500 starting watts — a 5,000W generator. Always check the nameplate on your AC for exact wattage.
Can a 2000W generator run a window AC?
A 2,000W generator (2,200W starting) can run a 5,000-6,000 BTU window AC (1,500W starting). It cannot run a 10,000+ BTU unit (3,000W+ starting). The Honda EU2200i (2,200W starting) is the minimum for a small window AC. For larger units, use a 3,500W+ generator.
Can a solar generator run a window AC?
Yes, but runtime is limited. A 5,000 BTU window AC draws 500W, so a 2,000Wh solar generator runs it for 4 hours. A 4,000Wh unit runs it for 8 hours. For a 10,000 BTU unit (1,000W), a 4,000Wh unit runs for 4 hours. Window AC is energy-intensive — a solar generator is best for short-term cooling, not all-day AC.
How many watts does a window AC use?
A 5,000 BTU window AC uses 500 running watts and 1,500 starting watts. A 10,000 BTU unit uses 1,000 running watts and 3,000 starting watts. A 15,000 BTU unit uses 1,500 running watts and 4,500 starting watts. Starting watts are 3x running watts because AC compressors use induction motors.
Can I run a window AC and a refrigerator on the same generator?
A 5,000 BTU window AC (500W) and a refrigerator (800W) together need 1,300 running watts. The challenge is starting watts: the AC needs 1,500W and the fridge needs 2,200W. If both start at the same time, you need 3,700W starting. A 5,000W generator like the Westinghouse iGen5000DFc can handle both with headroom.