How much does it cost to run air conditioning for 8 hours?

For a 2.5kW split unit at the Yorkshire cap rate of 25.60p per kWh, 8 hours costs between about 25p and £1.15. The low end is the unit ticking over in a shaded room. The high end is full output in a heatwave. Most bedroom nights in Leeds fall nearer the middle, around 50p to 60p.

How many kWh does an air conditioner use a day?

It depends on the hours and how hard it works. A 2.5kW unit drawing 0.28kW for 8 hours uses 2.24kWh. Running flat out for 10 hours on a very hot day, the same model would use 5.6kWh. Multiply your kWh by the pence per kWh on your bill for the cost.

Is it cheaper to leave air conditioning on all day?

Often, yes, at a moderate setting. An inverter unit is far more efficient when it is ticking over than at full output, so holding a room at 24°C can use less than cooling it from 29°C in the evening. Close the blinds as well, so the unit has less heat to remove.

Does the January 2027 price cap change these figures?

Yes, if you are on a standard variable tariff. Ofgem sets new rates every three months, and the cost per hour moves in step with the unit rate. Keep the kWh figures from this page and multiply them by the new Yorkshire rate. On a fixed tariff, your contract rate applies until it ends.

Why is my bill higher than the label says?

The label assumes a fixed number of full-load hours and a standard building. A loft room in a terrace, a low set point, a dirty filter or an undersized unit can all push use above it. Check the filter first, then raise the set point a degree and compare a week of meter readings.

Air Conditioning Running Costs UK 2026

The short answer

At the Yorkshire price cap rate of 25.60p per kWh, a certified 2.5kW wall-mounted split unit costs 14.3p an hour at full output and 3p to 7p an hour once the room is close to temperature. That is the range for most bedrooms and home offices in Leeds. In our worked example, a whole summer of use in one Leeds bedroom comes to £16.36.

The sum is always the same. Power drawn in kW, multiplied by hours, multiplied by your unit rate in pence. Everything else on this page is about getting those three numbers right for your home, and every figure is either linked to its source or marked as an assumption you can swap for your own.

Why a 2.5kW air conditioner does not use 2.5kW

The kW on the sales sheet is cooling output. It is not the electricity the unit uses.

A split air conditioner moves heat out of the room. It doesn't make cold, so it can shift several kW of heat for each kW of electricity. The Eurovent certificate for the Daikin FTXM25R / RXM25R9, a common 2.5kW bedroom unit, shows a cooling output of 2.50kW for an electrical input of 0.56kW at full load. That ratio, 2.50 / 0.56, is the EER of 4.50 printed on the same certificate.

We use that unit as the reference model on this page because its certified figures are public and independently tested. It isn't a recommendation. Other brands publish the same figures, and the method works for any of them.

The figures you need from a data sheet

Ask your installer for the data sheet or the Eurovent listing of the exact model they quote. Five lines on it do most of the work. For the reference unit they read as follows.

The certificate also lists part-load figures, called conditions B, C and D. These are the ones most guides leave out, and they are the reason real running costs are lower than the headline number.

2.50kW rated cooling capacity, the heat it can remove at full output.
0.56kW rated cooling power input, what it draws at full output with 35°C outdoors.
A SEER of 8.65, its seasonal efficiency in cooling.
101kWh a year of cooling energy on the label.
1W on standby and 6W with the thermostat off.

How much power it really draws on a Leeds summer day

An inverter unit slows its compressor once the room is near the set temperature. The certified part-load tests show how far. At condition B (30°C outdoors) the reference unit delivers 1.85kW of cooling at an EER of 6.54. At condition C (25°C outdoors) it delivers 1.19kW at an EER of 10.14.

Divide output by EER and you get the electricity drawn. Condition B is 1.85 / 6.54 = 0.28kW. Condition C is 1.19 / 10.14 = 0.12kW. So on a 25°C afternoon the unit may draw about a fifth of its full-load input, and on a 30°C day about half.

Those test points assume a standard building load, so a hot loft room will sit nearer the top of the range than a shaded ground floor room. They are still a far better guide to a normal Leeds day than the full-load figure, which is measured at 35°C outdoors.

Price per hour at the October 2026 cap

Ofgem's price cap for 1 October to 31 December 2026 sets an average electricity unit rate of 26.32p per kWh for Direct Debit customers in Great Britain. The rate for the Yorkshire region, which covers Leeds (LS), Bradford (BD), Wakefield (WF) and Huddersfield (HD) postcodes, is lower at 25.60p per kWh. Ofgem's postcode lookup puts Harrogate (HG1) in North Eastern England, where the rate is 25.46p.

Using the Yorkshire rate and the reference unit:

Electricity on these rates carries no VAT. HMRC's VAT Notice 701/19 sets a temporary zero rate on domestic electricity in Great Britain from 1 October 2026, and says the government has extended it to 30 June 2027. Ofgem resets the cap every three months, so the January to March 2027 rate will be different. Re-run the sums with the new figure when it is published.

At full load the sum is 0.56 x 25.60p = 14.3p an hour.
At condition B it is 0.28 x 25.60p = 7.2p an hour.
At condition C it is 0.12 x 25.60p = 3.1p an hour.
On the Great Britain average of 26.32p, full load is 0.56 x 26.32p = 14.7p an hour.

A calculator you can do on your phone

Step one: find the power input. Use the full-load figure from the data sheet for a heatwave, or the condition B or C figure (output divided by EER) for a typical warm day. If you only have the full-load figure, use it and treat the answer as a ceiling.

Step two: decide the hours. Count only the hours the unit is actually running, not the hours you are in the house.

Step three: find your unit rate. It is on your bill in pence per kWh. On a standard variable tariff in Leeds, it is the Yorkshire cap rate above. On a fixed or time-of-use tariff, use your own figure.

Step four: multiply kW x hours x pence, then divide by 100 for pounds. Leave the standing charge out, because you pay it whether the air conditioner runs or not. In Yorkshire it is 61.67p a day under the October 2026 cap.

Worked examples for four Leeds rooms

Each example uses the reference unit, the Yorkshire rate of 25.60p and a power level picked from the certified figures. The hours are assumptions. Change them to match how you live.

Attic bedroom in a back-to-back. Leeds City Council's housing strategy counts about 19,500 pre-1919 back-to-back houses still in use. The top room has one outside wall and a slate roof above it, so it stays warm long after sunset. Say the unit runs at condition B for 8 hours overnight: 0.28 x 8 = 2.24kWh, and 2.24 x 25.60p = 57.3p a night. If the room is so hot that the unit runs flat out all night, the ceiling is 0.56 x 8 x 25.60p = £1.15.

Home office in a 1930s semi. A back bedroom used as an office warms up through the afternoon. Say 4 morning hours at condition C and 4 afternoon hours at condition B: (0.12 x 4) + (0.28 x 4) = 0.48 + 1.12 = 1.60kWh. At 25.60p that is 41.0p for the working day.

City-centre flat living room. Upper-floor flats with large south or west glazing can hit full load on a hot evening, as our city-centre flat guide explains. Six hours at 0.56kW is 3.36kWh, which costs 86.0p.

Through-terrace bedroom in Headingley. The same dormer and loft heat problem as a back-to-back, covered in our terraced house guide, but with a window at each end of the house. With the blinds shut in the day, condition C for 6 evening hours might be enough: 0.12 x 6 = 0.72kWh, or 18.4p.

Working out a whole summer with the heatwave-days method

Monthly averages hide what drives the bill. The Met Office's historic station data for Bradford, the West Yorkshire station in its long-running historic data series, gives a July mean daily maximum of 20.4°C over 1991 to 2020. A unit barely needs to run on an average day like that. The cost comes from a handful of warm spells.

The Met Office defines a heatwave as at least three days in a row at or above a threshold set for each county, so a single hot afternoon doesn't count. For running costs, count days in three kinds and give each kind its own power level and hours. Here is one example for a single bedroom. The day counts are our assumption, so change them.

Total: 9.0 + 26.9 + 28.0 = 63.9kWh. At 25.60p that is £16.36 for the summer. At the Great Britain average of 26.32p it would be £16.82. The five heatwave days use 28.0kWh, close to the 35.9kWh of the other 37 days combined. That is why the number of very hot days matters more than the average temperature.

Summer 2026 shows why the count moves. The same Bradford record gives a provisional July 2026 mean daily maximum of 23.1°C, 2.7°C above the 1991 to 2020 July average, with only 4.6mm of rain all month. In a summer like that, add more hot and heatwave days to your count. Since 1991 only July 2006 (24.8°C) and July 2018 (24.3°C) have been warmer at that station.

25 warm evenings at condition C, 3 hours each: 25 x 3 x 0.12 = 9.0kWh.
12 hot days and nights at condition B, 8 hours each: 12 x 8 x 0.28 = 26.9kWh.
5 heatwave days at full load, 10 hours each: 5 x 10 x 0.56 = 28.0kWh.

Checking your answer against the energy label

The label figure is a useful cross-check. Under the energy labelling rules for air conditioners in Regulation 626/2011, Annex VII, annual cooling energy is based on 350 equivalent hours at full design load. The sum is capacity x 350 / SEER, so 2.5 x 350 / 8.65 = 101kWh, matching the 101kWh on the certificate.

At 25.60p, 101kWh costs £25.86 a year. The 350 hours is a European reference figure, not a Leeds measurement, so it is a sensible upper estimate for one room in a normal West Yorkshire summer. Our heatwave-days example came out at about two thirds of it. If your own sum comes out far above the label figure, check your hours.

Standby, thermostat-off and leaving it on

The reference unit draws 1W on standby and 6W when it is on but the thermostat has stopped the compressor. Left on standby all year, 1W is 0.001 x 24 x 365 = 8.76kWh, about £2.24. The thermostat-off figure only applies while the unit is switched on, so it adds pennies over a summer.

Leaving the unit running at a moderate set point through a hot afternoon can cost less than letting the room overheat and then running it flat out for an hour to catch up. The part-load figures above explain why. At condition C the unit gets roughly twice as much cooling from each kWh as at full load (EER 10.14 against 4.50).

Is air conditioning expensive to run compared with a portable?

A portable unit keeps the compressor in the room and pushes heat out through a hose, and warm air leaks back in around the window gap. Single-duct portables are tested and labelled differently from splits, so compare the input power on the data sheet. If a portable draws 1.0kW (an assumption, check your model) for 6 hours, that is 6kWh, or £1.54 at 25.60p. The split reference unit at full load for the same 6 hours costs 86.0p. Our fixed versus portable guide covers noise and comfort too.

Heating mode, briefly

Almost every split unit sold for UK homes is a reversible air-to-air heat pump. The reference unit has a SCOP of 5.10, so each kWh of electricity gives about 5.1kWh of heat on average over a season. At 25.60p that is 25.60 / 5.10 = 5.0p per kWh of heat. Yorkshire gas under the same cap is 7.90p per kWh, or 7.90 / 0.90 = 8.8p per kWh of heat through a boiler at an assumed 90% efficiency. A plug-in electric heater costs the full 25.60p.

Heating costs, grants and a full winter comparison are in our air-to-air heat pump guide. The Energy Saving Trust says there is little UK data on how these systems perform and suggests asking your installer to estimate running costs from their design.

What changes the figure for your home

Heat getting into the room is the biggest factor. Blinds on south and west windows during the day cut the work before the unit even starts. The Energy Saving Trust also advises trying shading and ventilation first.

Set temperature is next. Each degree lower means more heat to remove, and 23°C or 24°C usually feels comfortable once the air is drier.

Size matters as well. An undersized unit runs at full load most of the time, which is the most expensive way to run it. An oversized one cycles on and off. Our guide to sizing an air conditioner covers the heat-gain check a surveyor should do.

Last, efficiency. Compare the SEER of the models you are quoted. A unit with a SEER of 6 instead of 8.65 would use 2.5 x 350 / 6 = 146kWh on the label sum, 45kWh more a year, or about £11.52 at 25.60p.

Before you get a quote

Ask each installer for the exact indoor and outdoor model numbers, then look up the Eurovent certificate or data sheet. Note the full-load input, the condition B and C output and EER, and the SEER. With those and the Yorkshire rate, you can run every sum on this page yourself in five minutes.

Our partner installers are MCS certified and zero-rate VAT on domestic installs. For what the installation itself costs, see our Leeds installation cost guide. When you are ready, send us your room details and we will pass them to an installer covering Leeds, Bradford, Wakefield, Harrogate or Huddersfield.

Sources

Guidance is general and indicative. Always confirm details with a qualified F-Gas registered installer. Get a free quote.

How much does air conditioning cost to run in the UK?