Guide
Estimate pounds per day before treating air conditioning as a whole-bill mystery.
UK air conditioning is often seasonal, but heatwaves, bedrooms, home offices, and portable units can make cooling visible on the bill. The estimate should use p/kWh, runtime, and efficiency rather than assuming the cooling capacity is the electricity draw.
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Electricity rates
Ofgem
Use your supplier tariff first; price-cap rates are only a benchmark.
Appliance efficiency
Energy Saving Trust
Cooling cost depends on unit type, efficiency, room size, insulation, and thermostat setting.
Climate context
Met Office
Heatwave frequency and local summer temperature affect AC runtime.
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If the label or manual lists input watts, use that to cross-check the estimate. If you only know cooling capacity, divide capacity by COP to estimate input power. Portable units can be less efficient than fixed split systems, especially when exhaust heat leaks back into the room.
A 2.5 kW cooling unit at COP 3.0 uses about 0.83 kW while running. At 25p/kWh, five running hours costs about £1.04 per day. Over 30 hot days, that is roughly £31.
Annual averages can hide cooling cost because the load is concentrated into hot spells. Bedrooms, loft rooms, conservatories, and home offices may run for long periods during heatwaves even if annual AC use is low.
Cooling often overlaps daylight, so rooftop solar can offset part of the load. But the UK case still depends on roof output, SEG export value, and whether the AC runs into the evening.
Check shading, night ventilation, insulation, curtains, fan use, and room sealing first. A portable unit can be useful, but it should be costed using actual runtime and tariff.
Open the AC Running Cost Calculator