The running cost of an air conditioner depends on three things: how much electrical energy the system actually uses, how long it operates, and the price you pay per kilowatt-hour (kWh).

The simplest formula is:

Running cost = electricity consumed (kWh) × electricity unit rate.

For example, if an air conditioner averages 0.8kW of electrical input over an hour and your tariff is 26p/kWh, that hour would cost about 21p. If it averaged 1.2kW, the same hour would cost about 31p. These examples are illustrative; inverter systems continuously adjust their output, so actual consumption changes with room temperature, weather, set point and load.

A common mistake is to use cooling capacity as electrical consumption. A 3.5kW air conditioner can deliver around 3.5kW of cooling while drawing substantially less than 3.5kW of electrical power. This is why seasonal efficiency ratings matter.

In the UK, Ofgem’s energy price cap provides useful reference rates for households on default tariffs, but it is not everyone’s actual price. For 1 July to 30 September 2026, Ofgem publishes an average electricity unit rate of 26.11p/kWh for Direct Debit customers under the cap in England, Scotland and Wales. For 1 October to 31 December 2026, the average published rate is 26.32p/kWh. Fixed tariffs and regional rates can differ.

To estimate your own cost accurately, find the electricity unit rate on your bill. Then check the air conditioner’s rated input and seasonal performance data. A plug-in energy monitor can sometimes help with portable units, while fixed systems may need other monitoring arrangements.

Room conditions have a large effect. A correctly sized inverter system cooling a well-insulated bedroom to a sensible set point may reduce its power once the room reaches temperature. The same system in a sun-exposed loft room during a heatwave may work much harder.

You can reduce running cost by closing windows and doors while cooling, shading strong sunlight, cleaning filters, using sensible temperature settings and avoiding unnecessarily low set points. Pre-cooling a room moderately can also be more comfortable than waiting until it becomes extremely hot and then demanding maximum cooling.

When comparing products, look at SEER for seasonal cooling efficiency and the official energy label where applicable. For heating, compare SCOP as well. Higher seasonal efficiency can reduce energy consumption for the same useful output, although purchase price and usage patterns should also be considered.

Our product pages show capacity and efficiency information so you can compare suitable models. Use your actual electricity tariff in our running-cost calculator rather than relying on a national average.

Sources checked: Ofgem energy price cap unit rates and standing charges (ofgem.gov.uk). Rates are time-sensitive and should be updated regularly.