A 3-ton central air conditioner in North Dakota costs about $34.07 in July and $93.32 a year at 12.46¢/kWh; an 8,000 BTU window unit about $6.66 in July.
At 12.46¢/kWh — North Dakota average, Jan–Aug 2026 (EIA). That is 32% below the U.S. average of 18.19¢.
| Efficiency | Per year | vs yours |
|---|---|---|
| SEER2 13.4 (min · North) | $93.32 | — |
| SEER2 14.3 (min · South) | $87.45 | −$5.87 |
| SEER2 15.2 (ENERGY STAR) | $82.27 | −$11.05 |
| SEER2 17 (ES average) | $73.56 | −$19.76 |
| Month | Full-load hours | 3-ton central | 8,000 BTU window |
|---|---|---|---|
| April | 1 | $0.41 | $0.08 |
| May | 18 | $5.99 | $1.17 |
| June | 57 | $19.20 | $3.75 |
| July | 102 | $34.07 | $6.66 |
| August | 86 | $28.70 | $5.61 |
| September | 15 | $4.96 | $0.97 |
DOE's room-AC test assumes 750 full-load hours a year for a typical U.S. home. We scale it by North Dakota's population-weighted cooling degree days (452 ÷ 1,216) and spread it over the months the same way: 279 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. × 279 h = 749 kWh × 12.46¢ = $93.32.
The full method, material data and tips are on the main air conditioner cost calculator page.