Window AC
How much electricity does a window AC use?
500–1,500 W by BTU · $20–$60 per month · inverter units save 30–50%
Window air conditioners are rated in BTU, and watts track BTU closely: roughly 100 W per 1,000 BTU for a standard unit.
Watts by BTU
- 5,000 BTU (small bedroom) — 450–550 W
- 8,000 BTU (bedroom) — 700–800 W
- 10,000 BTU (large bedroom) — 900–1,000 W
- 12,000 BTU (living room) — 1,100–1,300 W
- 15,000 BTU (large room) — 1,400–1,600 W
Inverter units change the maths
Traditional units run the compressor flat out until the thermostat trips, then stop entirely. Inverter units ramp down and hold a steady output. In real use that is a 30–50% saving on the same room, and it eliminates the start-up surge of 2–3× rated wattage that plain units produce every cycle.
Sizing beats efficiency
Too small and it never catches up, running constantly. Too big and it cools the air before removing humidity, leaving the room cold and clammy, then shutting off and starting again. Size to the room, then buy the most efficient inverter model you can afford in that size.
Frequently asked questions
How many watts does a window ac use?
500–1,500 W by BTU. The figure on the rating label is the maximum draw; actual use varies with settings, age and usage pattern.
How much does it cost to run a window ac per month?
With the defaults above it comes to the monthly figure shown in the calculator. At 16.5¢/kWh — the US residential average — that is a realistic middle estimate. Your own bill may be 30% lower or higher depending on state.
Is it cheaper to run a window ac at night?
Only if your utility offers a time-of-use plan and you avoid the 4pm–9pm peak window. On a flat-rate plan, the time of day makes no difference to the total.
Does the calculator account for real-world duty cycles?
Not automatically — you enter the effective hours yourself. For compressing appliances like refrigerators and AC units, enter the running watts and roughly the proportion of time the compressor is on, which is usually 30–50%.
Will a newer window ac actually save money?
Compare the kWh figure in the calculator against an Energy Star model's stated annual use. If the difference is a few hundred kWh a year, the payback on a replacement is usually long; if it is over 500 kWh, it is worth pricing out.