Air conditioning running costs
An air conditioner’s running cost comes down to three things: how much electricity it actually draws (far less than its kW rating, thanks to the heat-pump effect), how many hours you run it, and your electricity unit price. The headline is that AC is usually cheaper to run than people fear — and for heating, it can be genuinely good value.
The key idea
- The kW rating is output, not consumption — see kW and BTU.
- Electricity drawn ≈ output ÷ efficiency.
- Running cost = electricity drawn (kW) × hours × your unit price (p/kWh).
- In heating mode, a heat pump delivers more heat than the electricity it uses, so it can undercut direct electric heating.
Working out your running cost — the method
- Take the unit’s output for the mode you’re using — say 3.5 kW of cooling.
- Divide by its efficiency to get the electricity it actually draws. With a cooling efficiency (SEER/EER) of around 3.5, a 3.5 kW unit draws roughly 1 kW.
- Multiply by the hours you run it. One kilowatt for one hour is one kWh, so 1 kW × 4 hours = 4 kWh.
- Multiply by your unit price. Say that’s 25p per kWh (broadly in line with 2026 average rates), then 4 kWh × 25p ≈ £1 for the day.
So that example room costs roughly £1 a day to cool for four hours. Your own figures will differ with the unit’s efficiency, how hard it works, and your tariff.
Tip
The 25p/kWh above is an illustrative rate to show the method — always check your own tariff, since rates change and vary by region.
Why heating can be a bargain
In heating mode the heat-pump effect works in your favour: a unit with a seasonal heating efficiency (SCOP) of 4 delivers about 4 kW of heat for every 1 kW of electricity. That can make it cheaper to run than a plain electric heater, and competitive with other forms of heating, because you pay for one unit of electricity and get several units of heat back. (This is not the same as an air-to-water heat pump for central heating — see grants and incentives for why that distinction matters.)
What pushes running costs up or down
Up: running it harder (very hot or cold days), poor insulation, large glazed or sunny rooms, an oversized or low-efficiency unit, and leaving it on when rooms are empty.
Down: a high-efficiency inverter unit, the right size for the room, good insulation, sensible thermostat settings, and using timers or zoning so you only condition the rooms in use.
Practical tips: set a sensible target temperature rather than an extreme one, use timers and any “eco” or sleep modes, keep the filters clean, and only run the rooms you’re using. Small habits add up over a season.