Cost to Run an Air Conditioner: Hourly, Daily and Monthly Calculator

The formula

An efficiency rating is cooling delivered per watt-hour. Divide the unit's capacity by its rating and you get the average power it draws while running; multiply by hours and your rate for the cost.

Average power (kW) = Capacity (BTU/h) ÷ (SEER2 × 1,000)
kWh per day = Average power × Compressor hours per day
Cost = kWh × Rate ($/kWh)

SEER2 is a seasonal average, so this gives a realistic figure across a typical summer. On a 100 °F afternoon the unit will draw more; for that peak figure, use the EER2 rating in the efficiency field instead. Window and through-wall units are rated in CEER, which you can enter directly. Portable units carry a SACC capacity and CEER on their label; enter both.

Worked example

Using the calculator defaults: a 2-ton (24,000 BTU/h) central air conditioner rated 14.3 SEER2, running 8 hours a day, at $0.17/kWh.

1. Average power: 24,000 ÷ (14.3 × 1,000) = 1.68 kW
2. Daily energy: 1.68 × 8 = 13.4 kWh
3. Daily cost: 13.4 × $0.17 = $2.28
4. Monthly (30 days): 403 kWh, about $68.48
5. Per hour of running: 1.68 × $0.17 ≈ $0.29

Swap in your own rate from your bill. Rates vary from under $0.12/kWh in some states to over $0.35/kWh in others, which alone can triple the answer.

Monthly cost by AC size

Assumes 8 compressor hours a day for 30 days at $0.17/kWh. Central systems at the 14.3 SEER2 southern minimum; room units at typical label ratings.

Upgrading efficiency scales cost down in proportion: the same 3-ton unit at 18 SEER2 would cost about $82 a month. The SEER2 savings calculator compares two systems over a full season.

How many hours does an AC actually run?

Compressor run time depends on weather, house and equipment size. A system sized to Manual J runs close to continuously only on the hottest design days. On a typical summer day it might run 40–70% of the time during the afternoon and much less overnight. Across a season, US homes see somewhere between a few hundred full-load hours in the far North and 2,500–3,500 in south Florida, Texas and Arizona.

An oversized system runs fewer hours but cycles more often and removes less humidity; its running cost isn't much lower and comfort is worse. If your unit turns on and off every few minutes, see AC short cycling, and check its size with the AC tonnage calculator.

Central AC vs mini-split vs window unit

Which type is cheapest to run depends on how much of the home you need to cool:

• Ductless mini-splits often rate 18–30 SEER2 and lose nothing to ducts, so cooling one or two zones with them can cost much less than running a central system for the whole house. Size each head with the mini-split sizing calculator.
• Central systems are usually the most economical way to cool a whole house, provided the ducts are tight and inside the conditioned space or well insulated.
• Window units are inexpensive to buy and fine for a single room, but most have lower efficiency than a modern central system or mini-split.
• Portable units are the least efficient per BTU because their hose and casing leak heat back into the room and they pull in warm outside air to replace what they exhaust.

If you are choosing between them, compare the cost per hour of delivering the same cooling using each unit's SEER2 or CEER in the calculator above.

Ways to cut the cost

• Raise the setpoint. Each degree warmer cuts the heat the system has to remove. DOE's guidance is that setting the thermostat back 7–10 °F for 8 hours a day can save up to about 10% a year on heating and cooling. See ideal AC temperature.
• Use a ceiling fan to feel 3–4 °F cooler at about 50 W. Turn it off when the room is empty; fans cool people, not rooms.
• Change the filter and keep the outdoor coil clean. Both restore airflow, which the rating assumes.
• Block afternoon sun on west and south windows with exterior shades or blinds.
• Seal and insulate attic ducts. Losses there are paid for twice: once to cool the air and again to cool the house it never reached.
• Run the AC before peak hours on time-of-use rates and let the house coast through the most expensive period.

Frequently asked questions