A 3-ton central air conditioner in Michigan costs about $73.09 in July and $205 a year at 21.73¢/kWh; an 8,000 BTU window unit about $14.29 in July.
At 21.73¢/kWh — Michigan average, Jan–Aug 2026 (EIA). That is 19% above the U.S. average of 18.19¢.
| Efficiency | Per year | vs yours |
|---|---|---|
| SEER2 13.4 (min · North) | $205 | — |
| SEER2 14.3 (min · South) | $192 | −$12.87 |
| SEER2 15.2 (ENERGY STAR) | $180 | −$24.22 |
| SEER2 17 (ES average) | $161 | −$43.31 |
| Month | Full-load hours | 3-ton central | 8,000 BTU window |
|---|---|---|---|
| May | 25 | $14.76 | $2.89 |
| June | 70 | $41.05 | $8.03 |
| July | 125 | $73.09 | $14.29 |
| August | 100 | $58.33 | $11.40 |
| September | 26 | $15.12 | $2.96 |
| October | 3 | $1.80 | $0.35 |
DOE's room-AC test assumes 750 full-load hours a year for a typical U.S. home. We scale it by Michigan's population-weighted cooling degree days (568 ÷ 1,216) and spread it over the months the same way: 350 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. × 350 h = 941 kWh × 21.73¢ = $205.
The full method, material data and tips are on the main air conditioner cost calculator page.