How much does it cost to run an air conditioner in Montana?

Short answer

A 3-ton central air conditioner in Montana costs about $23.18 in July and $58.07 a year at 14.13¢/kWh; an 8,000 BTU window unit about $4.53 in July.

• Montana pays 14.13¢/kWh on average for Jan–Aug 2026 — 22% below the U.S. average of 18.19¢, the 41st most expensive of the 50 states and DC.
• Montana averages 248 cooling degree days a year against 1,216 nationally (NOAA), so we estimate 153 full-load cooling hours — 2 a day in July.
• A new 3-ton split system sold for Montana must reach at least SEER2 13.4 (DOE northern region); it draws about 2.69 kW on average and $0.38 an hour.
• Moving up to the ENERGY STAR average of about SEER2 17 would cut the yearly bill to $45.77 — $12.30 a year less.
• The average Montana home used 853 kWh a month in 2025; this system adds 164 kWh in July.