A 3-ton central air conditioner in New Hampshire costs about $60.64 in July and $136 a year at 26.91¢/kWh; an 8,000 BTU window unit about $11.86 in July.
At 26.91¢/kWh — New Hampshire average, Jan–Aug 2026 (EIA). That is 48% above the U.S. average of 18.19¢.
| Efficiency | Per year | vs yours |
|---|---|---|
| SEER2 13.4 (min · North) | $136 | — |
| SEER2 14.3 (min · South) | $127 | −$8.53 |
| SEER2 15.2 (ENERGY STAR) | $120 | −$16.05 |
| SEER2 17 (ES average) | $107 | −$28.71 |
| Month | Full-load hours | 3-ton central | 8,000 BTU window |
|---|---|---|---|
| May | 5 | $3.57 | $0.70 |
| June | 30 | $21.40 | $4.18 |
| July | 84 | $60.64 | $11.86 |
| August | 62 | $45.04 | $8.81 |
| September | 7 | $4.90 | $0.96 |
DOE's room-AC test assumes 750 full-load hours a year for a typical U.S. home. We scale it by New Hampshire's population-weighted cooling degree days (304 ÷ 1,216) and spread it over the months the same way: 188 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. × 188 h = 504 kWh × 26.91¢ = $136.
The full method, material data and tips are on the main air conditioner cost calculator page.