A 3-ton central air conditioner in Maine costs about $53.60 in July and $114 a year at 30.23¢/kWh; an 8,000 BTU window unit about $10.48 in July.
At 30.23¢/kWh — Maine average, Jan–Aug 2026 (EIA). That is 66% above the U.S. average of 18.19¢.
| Efficiency | Per year | vs yours |
|---|---|---|
| SEER2 13.4 (min · North) | $114 | — |
| SEER2 14.3 (min · South) | $107 | −$7.19 |
| SEER2 15.2 (ENERGY STAR) | $101 | −$13.52 |
| SEER2 17 (ES average) | $90.02 | −$24.19 |
| Month | Full-load hours | 3-ton central | 8,000 BTU window |
|---|---|---|---|
| May | 1 | $1.00 | $0.20 |
| June | 17 | $13.52 | $2.64 |
| July | 66 | $53.60 | $10.48 |
| August | 52 | $42.08 | $8.23 |
| September | 5 | $4.01 | $0.78 |
DOE's room-AC test assumes 750 full-load hours a year for a typical U.S. home. We scale it by Maine's population-weighted cooling degree days (228 ÷ 1,216) and spread it over the months the same way: 141 hours a year. Your thermostat setting and insulation move this a lot — switch the calculator to your own hours if you know them.
3 tons = 36,000 BTU/h ÷ SEER2 13.4 = 2,687 W. × 141 h = 378 kWh × 30.23¢ = $114.
The full method, material data and tips are on the main air conditioner cost calculator page.