How Much Does It Cost to Run an Air Conditioner?

Power depends mainly on cooling capacity and efficiency. A 10,000–12,000 BTU room unit (about 1 ton, or 3–3.5 kW of cooling) typically draws 900–1,200 W with the compressor running. Once the room is cool, the compressor switches off and on, or slows down, to hold the thermostat setting, so averaged over an hour a typical unit uses about 60% of its full power: around 0.6 kWh.

At 8 hours a day that's about 4.8 kWh: roughly $0.87 a day in the US, £1.26 in the UK and €1.20 in Spain. Over a month it comes to about 146 kWh, or $26.50 in the US and €45.85 in Italy.

Bigger systems cost more. A 1.5-ton split AC, common in South Asia and the Middle East, can draw 1,500 W or more at full speed, and central air for a whole house often draws 2,500–4,000 W. In a heatwave or a poorly insulated room the compressor may run almost non-stop, so plan with the full-power figure for the hottest days.

Window units sit in a window opening with their hot side outdoors. Portable units stand inside the room and push hot air out through a hose. For the same cooling, portables generally use more electricity, because some heat leaks back into the room, and single-hose models pull warm outside air in through gaps.

Ductless mini-splits, or split ACs, have an indoor unit on the wall and a compressor outside. They are the most common type in much of Asia, Europe and the Middle East, and many are inverter models. Central air conditioning cools a whole house through ducts and draws the most power overall.

In the US and Canada, most small window units plug into a standard 120 V outlet, while larger units often need a dedicated 240 V circuit. In 230 V countries every size runs on the normal supply. Voltage doesn't change the cost; the watts and hours do.

EER (energy efficiency ratio) is cooling output in BTU per hour divided by power in watts, measured at one hot test condition. It lets you estimate power draw: a 12,000 BTU unit with an EER of 12 draws about 1,000 W. US room units carry a CEER rating, which works the same way but also counts standby power. SEER2 is the US seasonal rating for central and split systems; it averages efficiency over a range of outdoor temperatures, and the 2 marks the updated test procedure in use since 2023.

Other countries use their own seasonal ratings, such as SEER on EU energy labels and ISEER star ratings in India. Higher is better in every system, but the numbers aren't comparable between systems.

A non-inverter (fixed-speed) AC runs its compressor at full power until the room is cool, then switches off and back on. An inverter AC varies the compressor's speed, so once the room is cool it keeps running at low power instead. With long daily use, inverter models typically use noticeably less electricity and hold a steadier temperature.

The hotter it is outside and the cooler you set the thermostat, the longer the compressor runs. Sun on windows, poor insulation, an oversized or undersized unit and a dirty filter all push the cost up; shade, closed curtains and a sensible set point bring it down.

AC season runs roughly from May to September in the Northern Hemisphere and from November to March in the Southern Hemisphere. In the tropics and the Gulf, air conditioners may run for many hours a day all year, so a more efficient unit pays off faster there.

Figures are for the compressor and fans in cooling mode. To estimate a unit's power, divide its BTU/h rating by its EER, or use the input watts on its label.

• Set the thermostat to about 24–26°C (75–78°F). Each degree cooler makes the unit work harder.
• Run a fan alongside the AC: moving air feels cooler, so you can set the thermostat a couple of degrees higher.
• Clean or replace the filter regularly, about monthly in heavy use, and keep the outdoor unit clear of leaves and clutter.
• Close curtains or blinds on sunny windows, and keep doors shut so you only cool the room you're using.
• Use the timer or a smart thermostat instead of cooling an empty home all day.
• When buying, choose the right size and the best efficiency rating you can afford, and favour inverter models.

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