What does air conditioning cost to run?
Real figures from published efficiency data and the current price cap, with the arithmetic shown so you can check it against any unit you are quoted.
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The short answer
Cooling a bedroom with a 2.5kW wall mounted unit costs roughly 9p an hour to run, and a 5.0kW living room unit roughly 18p an hour, at the Ofgem price cap of 26.32p per kWh. Run eight hours a day through a hot spell, that bedroom unit is about £0.73 a day, or roughly £22 over a month of constant use. Those are estimates rather than quotes. The figure depends on the unit's seasonal efficiency, your tariff, the room, and how you set it.
The calculation
An air conditioner is rated by how much cooling it delivers, in kilowatts, not by how much electricity it draws. The number that connects the two is SEER, the seasonal energy efficiency ratio, which every manufacturer has to publish under the ecodesign rules. It is the cooling delivered across a whole season divided by the electricity consumed to deliver it.
That makes the sum straightforward. Capacity divided by SEER gives the average electrical draw in kilowatts. Multiply by the unit rate and you have pence per hour.
A 2.5kW unit with a SEER of 7.2 draws about 0.35kW on average. At 26.32p per kWh that is 9p an hour. The same arithmetic works for any unit you are quoted, and SEER is the figure to ask for, because it is measured to one standard and is therefore comparable between makes.
What each size costs to run
Using the seasonal efficiency published for the size, at the current price cap. The room descriptions are what each size is normally specified for.
| Size | Typical room | Published SEER | Cost per hour |
|---|---|---|---|
| 2.5kW | A bedroom or a study | 7.20 | 9p |
| 3.5kW | A larger bedroom | 7.20 | 13p |
| 5.0kW | A living room | 7.30 | 18p |
| 7.1kW | An open plan ground floor | 6.20 | 30p |
Estimates, not quotes. Based on the manufacturer's published seasonal efficiency for each size at the Ofgem price cap of 26.32p per kWh for 1 October to 31 December 2026, direct debit, England, Scotland and Wales.
Why the unit you choose changes the bill
The same 2.5kW of cooling, from five ranges we install. The capacity is identical. The electricity used to produce it is not.
| Range | Published SEER | Cost per hour |
|---|---|---|
| Daikin Comfora | 7.20 | 9p |
| Samsung Cebu S2 | 7.40 | 9p |
| Samsung WindFree Comfort S2 | 7.90 | 8p |
| Daikin Stylish | 8.74 | 8p |
| Daikin Perfera | 9.47 | 7p |
Seasonal efficiency figures as published by Daikin and Samsung for each unit at 2.5kW.
The gap is smaller than it looks, and bigger than it looks
Across a single hour, the difference between the least and most efficient 2.5kW unit we fit is a couple of pence. That is not a reason to spend hundreds more upfront, and anyone telling you the efficient unit pays for itself over a summer is not doing the arithmetic.
Over a decade of use it adds up to real money, and it matters much more if the unit is doing the heating too, because heating runs for far more hours of the year than cooling does in this country. If you expect to lean on it in winter, efficiency is worth paying for. If it is a fortnight of August relief, it is not.
What actually moves your bill
The published figure is an average across a season. These are the things that push your real cost above or below it.
How you set the thermostat
Setting 18 degrees when you want 23 does not cool the room faster, it just runs the compressor harder for longer and overshoots. Set the temperature you actually want and leave it there. An inverter unit is at its most efficient holding a temperature, not chasing one.
Whether the unit is the right size
An oversized unit cools the room quickly, switches off, and cycles. Cycling is the least efficient way to run a heat pump, so an oversized unit can cost more to run than a correctly sized one in the same room. This is the main reason we size from the room rather than from a price list.
Your tariff, not the price cap
The price cap is a cap on the unit rate, not a fixed national price, and plenty of tariffs sit below it. Every figure here uses 26.32p per kWh so the comparison is consistent; if you are on a cheaper rate, scale the numbers down proportionally.
The room itself
A south facing room with large windows and no shading takes more work to hold at temperature than a north facing one with the same floor area. Insulation, glazing and solar gain move the real figure more than the choice between two similar units does.
The standing charge, which is not the unit's fault
Your electricity bill carries a daily standing charge whether the air conditioning runs or not. It is not part of the running cost of the unit and none of the figures here include it.
Running it as a heater
The same unit heats, and heating is where the efficiency figure earns its keep. The heating equivalent of SEER is SCOP, and the ranges we fit publish seasonal figures between roughly 4.0 and 5.2 depending on the unit and the size.
A SCOP of 5.0 means five units of heat for every unit of electricity. That is the mechanism that makes a heat pump cheap to run in a way a fan heater or an electric radiator can never be, because those are capped at one to one.
The ranges this applies to
Every price is fully installed and includes the unit, the installation, the electrical work and VAT.
Instant estimate
Want the figure for your room?
The instant estimate sizes the room first, which is what decides the running cost. It takes about a minute and gives you a starting price with it.