How to work out what an air conditioner costs
Every efficiency rating on an air conditioner is BTUs of cooling per watt-hour of electricity, so the running power is simply capacity ÷ efficiency. Window units use CEER, central systems SEER2 (seasonal average) and EER2 (a 95°F afternoon). Multiply the watts by the hours the compressor actually runs and by your price per kWh.
Worked example — a 3-ton central AC at SEER2 14.3: 3 tons is 36,000 BTU/h. 36,000 ÷ 14.3 = 2,517 W, or 2.52 kW. At the U.S. average of 18.19¢/kWh that's $0.46 for every hour it runs. Over DOE's 750-hour cooling year: 1,888 kWh, about $343.
Window AC wattage and cost by size
| Size | ENERGY STAR avg CEER | Watts | Per hour | Per 750 h year |
|---|---|---|---|---|
| 5,000 BTU | 14.07 | 355 | $0.06 | $48.48 |
| 6,000 BTU | 14.21 | 422 | $0.08 | $57.60 |
| 8,000 BTU | 15.23 | 525 | $0.10 | $71.66 |
| 10,000 BTU | 15.35 | 651 | $0.12 | $88.88 |
| 12,000 BTU | 15.2 | 789 | $0.14 | $108 |
| 14,000 BTU | 15.47 | 905 | $0.16 | $123 |
| 18,000 BTU | 15.23 | 1,182 | $0.21 | $161 |
| 24,000 BTU | 13.35 | 1,798 | $0.33 | $245 |
Averages are from ENERGY STAR's certified window units. A federal standard for units made from May 26, 2026 raises the minimum to CEER 16.0 for 8,000–19,900 BTU — higher than today's ENERGY STAR average at those sizes, which still includes older models.
Central air by tonnage
| Size | SEER2 13.4 | SEER2 14.3 | SEER2 17 |
|---|---|---|---|
| 2 ton | $244 / yr | $229 / yr | $193 / yr |
| 3 ton | $367 / yr | $343 / yr | $289 / yr |
| 4 ton | $489 / yr | $458 / yr | $385 / yr |
| 5 ton | $611 / yr | $572 / yr | $482 / yr |
Yearly cost over 750 full-load hours at 18.19¢/kWh. New split systems must reach SEER2 13.4 in the North and 14.3 in the Southeast and Southwest (13.8 for systems of 45,000 BTU/h and up there). ENERGY STAR's certified 3-ton systems average SEER2 17.06.
How many hours will it run where you live?
Run time is the biggest unknown. The calculator starts from DOE's 750 full-load hours a year — the basis of every room-AC energy label — and scales it by your state's cooling degree days from NOAA. Florida has 2.8 times the U.S. average, Texas 2.2, Arizona 2.4, while Washington has 0.16. The result is spread over the months in proportion to each month's degree days, so you can see what July costs as well as the year. If you know your own habits, switch to custom hours: count the hours the compressor runs, not the hours the system is set to "cool."
Ways to cut the cooling bill
- Raise the setpoint and use ceiling fans; an ENERGY STAR fan averages 35 W on high, about 1/70 of a 3-ton system.
- Change filters on schedule and keep the outdoor coil clear so the system delivers its rated efficiency.
- Shade sun-facing windows in the afternoon, when the cooling load and many time-of-use peak prices both land.
- When replacing, compare the yearly cost at SEER2 14.3 and 17+ for your state — the difference repeats every summer.
- For one or two rooms, a correctly sized window unit or mini-split costs far less than cooling the whole house.
Common mistakes
- Using EER2 for the whole season. EER2 is measured at 95°F. Over a season the average draw is closer to capacity ÷ SEER2.
- Counting hours the system is "on." A thermostat cycles the compressor; only running hours cost money.
- Old SEER ratings. Minimums like "13 SEER" or "14 SEER" predate the 2023 SEER2 test; use SEER2 numbers with SEER2 minimums.
Also see the dehumidifier cost calculator for damp summers, your state's electricity rate, and the solar calculators if a big cooling bill has you thinking about panels.