Costs and running · 7 min read
How Much Does Air Conditioning Cost to Run Per Hour?
The number on the box is output, not consumption. Once you understand the difference, running costs stop looking frightening.
Published 2026-07-20 · Updated 2026-07-20 · WDI Group (Surrey) Ltd
Output kilowatts are not consumption kilowatts
A 3.5kW air conditioning unit does not use 3.5kW of electricity. That figure is the heating or cooling it delivers into the room. Because a heat pump moves heat rather than creating it, it typically delivers three to five units of heating or cooling for every unit of electricity it draws.
So the same 3.5kW unit might be drawing somewhere around 0.7kW to 1.1kW at steady state, and considerably less once the room has reached temperature.
A worked example
Take a bedroom unit drawing an average of 0.6kW over an evening, at a unit rate of 25p per kWh. That is roughly 15p an hour. Run it for four hours before bed on a hot night and you are at around 60p.
Use your own tariff rate to redo the sum — unit rates move, and the point of the method is that it stays valid when prices change.
- Cost per hour = average power drawn (kW) × your unit rate (p/kWh)
- Average draw is well below the rated output on an inverter system
- A whole-house figure is the sum of the units actually running
Duty cycle is what really decides the bill
An inverter system ramps hard to pull a room down to temperature, then throttles back to a low modulating output to hold it there. Most of the running time is spent in that low state, which is why measured costs are usually far lower than a back-of-envelope calculation based on full output.
Well-insulated rooms, closed doors, drawn blinds during the day and a sensible set point all shorten the hard-work phase.
In heating mode the sums are even better
Running in heating, an air-to-air heat pump typically produces three to four kilowatts of heat per kilowatt of electricity in British conditions. Compared with a direct electric heater at one for one, it is a fraction of the cost for the same warmth.
For heating one or two rooms in shoulder season, it is often cheaper to run the air conditioning than to fire the whole gas system for the house.
Frequently asked questions
- How can I measure it exactly in my own home?
- Read your smart meter or in-home display with everything else off, run the unit for an hour, and read again. That gives you the real figure for your property and your tariff.
- Does leaving it on all day cost more than switching it on and off?
- Usually a steady low set point costs less than repeatedly letting a room heat up and dragging it back down, because the compressor spends less time at full output.