Air-conditioner electricity consumption cannot be determined from the model’s cooling capacity alone. A system advertised as 2.5kW or 3.5kW is describing how much cooling it can deliver under specified conditions, not necessarily how much electrical power it draws.

To estimate consumption, look for the manufacturer’s rated input power, seasonal efficiency and energy-label information. Inverter systems vary their compressor speed, so power draw changes as the room approaches the set temperature.

Suppose a system averaged 0.7kW of electrical input for four hours. It would use approximately 2.8kWh of electricity. At 26p/kWh, that would cost roughly 73p. If another system averaged 1.0kW for four hours, it would use 4kWh and cost about £1.04 at the same rate. These are examples only.

Ofgem’s average capped electricity unit rate for Direct Debit customers in England, Scotland and Wales is 26.11p/kWh for 1 July to 30 September 2026. The published average for 1 October to 31 December 2026 is 26.32p/kWh. Your own tariff, region and payment method may produce a different figure.

Usage varies dramatically with weather. During a mild day, an inverter system may reduce output after reaching the desired room temperature. During a severe heatwave in a sunny top-floor room, it may operate at a much higher load.

Temperature setting matters. Setting the thermostat extremely low does not make the room cool instantly; it can simply make the system work harder and longer. A comfortable, moderate set point generally uses less energy than demanding a very low temperature.

Building factors matter too. Closing windows, reducing direct solar gain with blinds or shading, improving insulation and keeping filters clean can all reduce the cooling demand.

When comparing products, SEER is useful because it represents seasonal cooling efficiency rather than one instant operating point. For systems used for heating, SCOP provides the corresponding seasonal heating measure.

Our running-cost calculator lets you enter your own electricity tariff and expected daily hours. That produces a more meaningful estimate than a generic national cost.

Sources checked: Ofgem energy price cap unit rates and standing charges (ofgem.gov.uk). Always use your current electricity bill for the most accurate calculation.