How to calculate AC running cost
An air conditioner's electricity use depends on its cooling capacity and its efficiency. The EER (Energy Efficiency Ratio) printed on the EnergyGuide label tells you how many BTU of cooling the unit delivers per watt. Divide the capacity by EER to get the power draw while the compressor runs, then multiply by the hours it actually runs and your electricity price.
Watts = BTU/h ÷ EER · Cost = watts ÷ 1000 × running hours × price per kWh
Typical running costs at $0.17/kWh
| Unit | Power when running | Cost per running hour | 8 h/day for a month* |
|---|
| 6,000 BTU window (EER 11) | ≈ 545 W | ≈ $0.09 | ≈ $16 |
| 10,000 BTU window (EER 11) | ≈ 910 W | ≈ $0.15 | ≈ $26 |
| 10,000 BTU portable (EER 7.5) | ≈ 1,330 W | ≈ $0.23 | ≈ $38 |
| 12,000 BTU mini-split (EER 13) | ≈ 920 W | ≈ $0.16 | ≈ $26 |
| 3-ton central AC (EER 11.5) | ≈ 3,130 W | ≈ $0.53 | ≈ $89 |
*With the compressor running about 70 % of the time.
EER, CEER and SEER2
- EER measures efficiency at one hot condition (95 °F outdoors) – the best figure for estimating peak cost.
- CEER (Combined EER) on window units also includes standby power.
- SEER2 on central systems and mini-splits averages efficiency over a season; seasonal costs are usually lower than an EER-based estimate.
- Portable ACs are labeled with SACC (seasonally adjusted cooling capacity), which is lower than their nominal BTU.
Ways to cut the bill
- Choose the right size – an oversized unit cycles on and off and wastes energy.
- Set the thermostat to 78 °F (26 °C) when home and higher when away.
- Use ceiling or table fans to feel cooler at a higher setpoint.
- Close curtains on sun-facing windows and seal gaps around window units.
- Clean filters monthly and keep outdoor coils clear of leaves and dirt.
- Replace old units: an AC from before 2010 may use 20 – 40 % more electricity than a new ENERGY STAR model.
Frequently asked questions
How much does it cost to run an AC for an hour?
About $0.09 – $0.25 for a typical window or portable unit and $0.40 – $0.70 for a central system at $0.17/kWh.
How many watts does a 10,000 BTU air conditioner use?
Roughly 800 – 1,000 W for a window unit and 1,200 – 1,400 W for a portable unit while the compressor runs.
Is a portable AC more expensive to run than a window AC?
Usually yes – portable units are typically 25 – 40 % less efficient than window units of the same capacity.
Does running the AC all day cost more than turning it off?
For most homes, raising the thermostat while you're out saves energy compared with keeping it cool all day.
What is EER on an air conditioner?
Energy Efficiency Ratio – BTU of cooling per watt of electricity at standard conditions. Higher EER means lower running cost.
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CoolBill is an independent, free calculator for estimating air conditioner electricity use and cost. Efficiencies are typical values for each type; your unit's label (EER, CEER or SEER2) gives a more precise result. We are not affiliated with any appliance brand or utility.
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