How to calculate AC running cost
An air conditioner's cost depends on how much power it draws, how long it's on, how often the compressor actually runs, and your electricity rate.
- Find the power draw. Divide cooling capacity by efficiency: 8,000 BTU ÷ EER 11 ≈ 727 W.
- Apply the duty cycle. At 60%, the average draw is about 436 W.
- Multiply by hours and your rate. 436 W for one hour is 0.44 kWh — about $0.076 at 17.5¢/kWh.
Cost = (BTU ÷ EER) × Duty cycle × Hours ÷ 1,000 × Price per kWh
What different air conditioners cost to run
Typical costs for 8 hours a day with the compressor running 60% of the time, at 17.5¢/kWh — the U.S. average residential rate (EIA, 2025). Season = 4 months.
| Air conditioner | Power | Per month | Per season |
|---|---|---|---|
| Window AC · 5,000 BTU | 455 W · EER 11 | $11.61 | $46.45 |
| Window AC · 8,000 BTU | 727 W · EER 11 | $18.58 | $74.33 |
| Window AC · 12,000 BTU | 1,111 W · EER 10.8 | $28.39 | $113.56 |
| Portable AC · 10,000 BTU | 1,176 W · EER 8.5 | $30.06 | $120.24 |
| Ductless mini-split · 12,000 BTU | 960 W · EER 12.5 | $24.53 | $98.11 |
| Central AC · 3 ton (36,000 BTU) | 3,000 W · EER 12 | $76.65 | $306.60 |
Tips to cut cooling costs
- Raise the thermostat when you're home and more when you're away — a smart thermostat does it for you.
- Clean or replace filters regularly; a clogged filter makes the compressor run longer.
- Block afternoon sun with blinds or curtains and seal gaps around window units.
- Size the unit to the room: an oversized AC short-cycles, an undersized one never stops.
Frequently asked questions
How much does it cost to run an air conditioner per hour?
It depends on size and efficiency. An 8,000 BTU window unit with an EER of 11 draws about 727 W while cooling. With the compressor running 60% of the time at 17.5¢/kWh, that is roughly $0.076 per hour.
How much does it cost to run central air per month?
A typical 3-ton central AC (EER 12) running 8 hours a day with a 60% duty cycle costs about $76.65 per month at 17.5¢/kWh. Hot climates, long run times and higher rates push this up quickly.
How do I convert BTU to watts for an air conditioner?
Divide the cooling capacity in BTU per hour by the unit's EER (Energy Efficiency Ratio). A 12,000 BTU unit with an EER of 12 draws about 1,000 W while the compressor runs.
What is the compressor duty cycle?
An air conditioner doesn't run at full power the whole time it's switched on. Once the room reaches the thermostat setting, the compressor cycles off and on. The duty cycle is the share of time it actually runs — often around half, more on very hot days.
How can I lower my AC costs?
Set the thermostat a few degrees higher, use a programmable or smart thermostat, keep filters clean, close blinds on sunny windows and seal air leaks. Choosing a unit with a higher EER or SEER2 rating lowers the cost of every hour it runs.
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