Last Updated on August 28, 2026
If the only thing putting you off air conditioning is the fear of a horror electricity bill, the real numbers are far friendlier than most people assume. A modern wall-mounted unit can cool a bedroom for under 10p an hour at current electricity prices.
This guide breaks down air conditioning running costs using the July to September 2026 Ofgem price cap, with worked examples for different room sizes, full-summer costs, comparisons with portable units and fans, and what heating mode could mean for your winter bills.
Contents
The short answer
At the Ofgem price cap for 1 July to 30 September 2026, electricity on a standard direct debit tariff costs an average of 26.11p per kWh.
A 2.5 kW wall-mounted split system sized for a typical double bedroom draws far less than 2.5 kW of electricity because that figure describes its cooling output, not its electrical consumption.
Using a seasonal efficiency figure of SEER 7, the average electrical draw works out at around 0.36 kW, or roughly 9p per hour at the current price cap.
Run it for six hours a day across a ten-week summer and the electricity cost comes to around £39. A comparable portable air conditioner could cost closer to £110 over the same period, while a 60W pedestal fan would cost around £6.60.
How the maths works
The key figure is SEER: the seasonal energy efficiency ratio. It describes how much cooling a unit delivers for each unit of electricity consumed across a representative cooling season, including part-load operation.
Current wall-mounted systems can achieve strong figures. The source material lists the Daikin Sensira at SEER 6.5, Mitsubishi MSZ-AP at 7.4, Panasonic Etherea at 8.5 and Viessmann Vitoclima 232-S at 9.
Using a mid-range SEER of 7:
2.5 kW cooling ÷ SEER 7 = 0.36 kW average electrical consumption
0.36 kW × 26.11p = roughly 9p per hour
At SEER 6.5, the equivalent calculation comes to around 10p an hour. At SEER 9, it falls to roughly 7p.
On the hottest afternoons, the compressor can consume more than the seasonal average. A typical split system might draw around 0.5 to 1.2 kW while working hard, equivalent to approximately 13p to 31p an hour at the current rate.
For estimating use across an entire summer, however, the seasonal efficiency figure gives a more useful comparison.
You can compare current models and their efficiency ratings in our best air conditioning units UK guide.
Split vs portable vs fan: cost per hour
Portable and fixed air conditioners perform the same basic job but can use very different amounts of electricity to deliver it.
A typical portable unit has an EER of around 2.0 to 2.8, compared with roughly 3.5 to 5.0 for an equivalent wall-mounted split under rated conditions.
One reason is the exhaust hose. A single-hose portable air conditioner pushes hot air outside, which can create negative pressure and draw warmer air back into the room from elsewhere in the property.
| System | Typical draw | Cost per hour at 26.11p/kWh |
|---|---|---|
| 2.5 kW split, SEER 7 | 0.36 kW average | ~9p |
| 3.5 kW split, SEER 7 | 0.50 kW average | ~13p |
| 5.0 kW split, SEER 7 | 0.71 kW average | ~19p |
| Portable, 2.5 kW cooling | 0.9 to 1.25 kW | 23p to 33p |
| Pedestal fan, 60W | 0.06 kW | ~1.6p |
A fan wins easily on running cost, but it is doing a different job.
Fans move air across your skin and make you feel cooler. They do not actively remove heat from the room. An air conditioner lowers the actual indoor temperature and removes moisture from the air.
Worked examples by room size
Using SEER 7 and an electricity price of 26.11p per kWh gives a useful indication of what different systems could cost.
Double bedroom: 2.5 kW unit
Average electrical consumption works out at around 0.36 kW, equivalent to approximately 9p an hour.
Eight hours of operation would therefore cost roughly 75p using the simple seasonal-average calculation.
Actual overnight consumption can be lower once an inverter system reaches the target temperature and reduces its output.
Living room: 3.5 kW unit
Average consumption at SEER 7 works out at approximately 0.5 kW, or around 13p an hour.
Six hours through a hot afternoon and evening would cost roughly 78p.
Large open-plan space: 5.0 kW unit
Average consumption works out at around 0.71 kW, or approximately 19p an hour.
Six hours of operation would therefore cost around £1.12.
These are illustrative averages rather than guaranteed bills. A well-insulated room with blinds closed against direct sun can require considerably less cooling than a south-facing space with large areas of glazing.
What a full summer could cost
Assume six hours of use per day across ten weeks of summer. That gives 420 operating hours.
| Setup | Estimated electricity used | Estimated season cost |
|---|---|---|
| 2.5 kW split, SEER 7 | 150 kWh | ~£39 |
| 3.5 kW split, SEER 7 | 210 kWh | ~£55 |
| 5.0 kW split, SEER 7 | 300 kWh | ~£78 |
| Portable, 2.5 kW cooling, EER 2.5 | 420 kWh | ~£110 |
| Pedestal fan, 60W | 25 kWh | ~£6.60 |
That puts the running-cost difference between an efficient split system and a portable air conditioner at around £70 over this example summer for a single room.
The trade-off is upfront cost. A fixed split requires professional installation, while a portable can simply be bought from a retailer and plugged in.
Our air conditioning installation cost UK guide covers that side of the calculation in detail.
If you only want cooling for a few exceptionally hot days each year, a portable unit can still make financial sense. If you expect to use air conditioning regularly for years, the efficiency, lower noise and heating capability of a fixed split become much more valuable.
Heating mode: the figure most people miss
Nearly every modern fixed split air conditioner is reversible, which means it can operate as an air-to-air heat pump during winter.
This changes the economics considerably because you are buying a heating system as well as a cooling system.
Our comparison of an air source heat pump vs an air conditioner explains how the technologies overlap.
For heating, the equivalent seasonal efficiency figure is SCOP.
Using the source draft’s illustrative SCOP range of 3.0 to 4.0, and comparing electricity at 26.11p per kWh with gas at 7.33p per kWh and a boiler operating at 90% efficiency:
| Heating method | Approx. cost per kWh of useful heat |
|---|---|
| Gas boiler at 90% efficiency | ~8.1p |
| Air-to-air system at SCOP 3.0 | ~8.7p |
| Air-to-air system at SCOP 3.5 | ~7.5p |
| Air-to-air system at SCOP 4.0 | ~6.5p |
On those assumptions, an efficient air-to-air system with a SCOP of around 3.5 or higher can compete with gas on the cost of useful heat.
That does not mean an air conditioner will automatically be cheaper than a gas boiler for every household. The comparison depends on the exact unit, outdoor temperatures, electricity tariff, boiler efficiency and which rooms you need to heat.
For the wider comparison, see our guide to heat pump running costs.
How to cut air conditioning running costs
Set a sensible temperature
Setting the room to 22°C to 24°C rather than trying to reach 18°C reduces how hard the compressor has to work.
The larger the difference between the indoor target and outdoor temperature, the more work the system has to do.
Keep windows and doors closed
An air conditioner is trying to remove heat from a defined space. Leaving windows or external doors open continuously introduces warm outside air and increases the cooling load.
Keep the filters clean
Dirty filters restrict airflow and can reduce system performance. Follow the manufacturer’s cleaning and servicing instructions rather than waiting until the unit visibly struggles.
Choose an inverter system
Modern inverter compressors vary their output rather than repeatedly operating at full power and switching off.
Once the room reaches the required temperature, the system can reduce its output and maintain the temperature more efficiently.
Stop heat entering the room
Close blinds or curtains before strong afternoon sun reaches the room, particularly on south- and west-facing windows.
Reducing the heat entering the property means the air conditioner has less work to do.
Pair air conditioning with solar
Solar panels and air conditioning can be a particularly useful combination because cooling demand often peaks during bright summer weather when solar generation is also high.
We’ve covered how many solar panels you need to run an air conditioner and whether a solar battery can run an air conditioner separately.
Does a multi-split cost more to run?
A multi-split system connects several indoor units to a single outdoor condenser.
Naturally, cooling three rooms generally consumes more electricity than cooling one. But you do not necessarily have to run every indoor unit simultaneously or at the same temperature.
A multi-split can therefore be useful if you want targeted cooling in several parts of the property without installing a separate outdoor unit for every room.
Our split vs multi-split air conditioning guide covers the installation and performance differences.
FAQs
How much does air conditioning cost per month in the UK?
Using the July to September 2026 electricity price cap and a seasonal efficiency of SEER 7, a 2.5 kW bedroom unit running for six hours a day works out at around £17 per 30-day month.
A 3.5 kW unit on the same usage pattern comes to roughly £24.
Actual consumption depends on weather, insulation, system efficiency and temperature settings.
Is a portable air conditioner cheaper to run than a split system?
Generally, no.
A portable unit is much cheaper to buy, but its lower efficiency means it can consume substantially more electricity to deliver a similar amount of cooling.
That can still be an acceptable trade-off if you only use it for a handful of days each year.
Is it expensive to leave air conditioning on all day?
Not necessarily.
Using the seasonal-average calculation above, a 2.5 kW split at around 9p per hour would cost roughly £1.08 across 12 hours.
Real consumption varies throughout the day because an inverter system reduces its output after the room reaches the target temperature.
Does heating with air conditioning cost more than gas?
It depends on the unit’s seasonal heating efficiency.
Using the current price-cap figures in this article, an air-to-air system achieving a SCOP of 3.5 works out at approximately 7.5p per kWh of useful heat, compared with around 8.1p from a 90% efficient gas boiler.
That comparison can change as electricity and gas prices move.
Our Verdict
Air conditioning running costs are considerably lower than many households expect.
At the July to September 2026 electricity price cap, a properly sized wall-mounted split can cost around 7p to 13p an hour for a typical bedroom or living-room installation when estimated using seasonal efficiency.
Over a ten-week summer, our examples put a single-room split at roughly £39 to £55 in electricity when used for six hours a day.
Portable units are cheaper to buy but substantially less efficient, while fans cost very little to run but cannot actually lower the room temperature.
The bigger financial decision is therefore usually the upfront installation cost rather than the summer electricity bill. If you expect to use the system regularly, the ability of a modern split to provide efficient heating during colder months strengthens the case further.
Sources
- Ofgem – Changes to the Energy Price Cap Between 1 July and 30 September 2026 (accessed 27 August 2026)
- GOV.UK – VAT on Energy-Saving Materials and Heating Equipment (accessed 27 August 2026)
- Heatable – Best Wall-Mounted Air Conditioning Units (accessed 27 August 2026)
- Heatable – Air Conditioning Running Costs (accessed 27 August 2026)
- WarmZilla – Split System vs Portable Air Conditioning (accessed 27 August 2026)
- Micro-Climate – Portable Air Conditioner Pros and Cons (accessed 27 August 2026)
- UK Energy Management – Heat Pump Running Costs (accessed 27 August 2026)
- Small Living Solutions – Fan Running Cost UK (accessed 27 August 2026)
