How much does air conditioning cost to run in the UK?
A typical 2.5kW bedroom unit costs roughly 20p to 25p per hour while actively cooling at current electricity prices, and less once the room reaches temperature. A full night's sleep cooling costs 50p to £1; a heatwave month of daily use lands between £15 and £30 per room.
The maths is simple once you know one number: the unit's power draw. A 2.5kW-output split draws roughly 0.6 to 0.8kW of electricity while cooling hard, because heat pumps move heat rather than generate it. Multiply by your unit rate (around 27p to 29p per kWh as we write this) and an hour of full-effort cooling costs about a quarter.
Real use costs less than that, because modern inverter units do not run at full effort for long. They pull the room down to temperature, then modulate to a trickle to hold it. An evening in a cooled living room might meter at 1 to 2kWh total. This is also why leaving the unit to hold a temperature often beats blasting it from scratch each time.
For comparison: the portable units people buy in desperation draw similar power for roughly half the cooling effect, because their hot exhaust hose leaks heat back into the room. Per degree of comfort, a properly installed split is the cheapest cooling you can run in a UK home.
In winter the same unit heats at the same efficiency advantage: roughly three kilowatts of heat per kilowatt of electricity. Run the numbers against a plug-in electric heater and the split wins by two-thirds; the comparison with mains gas is closer and depends on your tariffs.
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