The average UK air conditioning unit costs between 15p and 45p per hour to run, depending on the unit’s power rating and your electricity tariff, according to the Energy Saving Trust (Energy Saving Trust, 2026). A typical 2.5kW portable unit costs around 30p per hour at the current average electricity rate of 29p per kWh in the UK.
The exact running cost per hour is determined by the unit’s cooling capacity in kilowatts (kW) and your electricity rate. Portable air conditioning units generally consume 1kW to 3kW per hour of use, while fixed split systems are more efficient, often using 0.8kW to 2kW per hour. The figure also varies by the Energy Efficiency Ratio (EER), which measures cooling output per watt of electricity. For example, a unit with a higher EER rating uses less power to produce the same cooling effect, lowering your hourly cost.
Portable units cost 20p to 45p per hour
A standard portable air conditioning unit with a 2.5kW cooling capacity typically draws around 1.2kW of electrical power. At the UK average electricity rate of 29p per kWh, this works out at roughly 35p per hour. Larger portable units with 3.5kW capacity can cost up to 45p per hour, while smaller 1.5kW models cost around 20p per hour (GOV.UK, 2026). These costs assume the unit runs continuously at full power, which is rare in practice as thermostats reduce usage once the room reaches the set temperature.
Split system units cost 15p to 30p per hour
Fixed split-system air conditioners are more energy-efficient than portable models. A 2.5kW split unit with an EER of 3.5 uses roughly 0.7kW of electricity per hour, costing around 20p at the standard rate. High-efficiency models with an EER of 4.0 or above can reduce this to 15p per hour (Energy Saving Trust, 2026). These units also benefit from inverter technology, which adjusts compressor speed to maintain temperature without cycling on and off, further lowering average running costs.
Electricity tariff and usage patterns affect cost
Your actual cost per hour depends on your specific electricity tariff. At the current UK average of 29p per kWh, a 1.2kW portable unit costs 35p per hour, but on a cheaper fixed tariff of 24p per kWh, that drops to 29p per hour. Economy 7 tariffs can reduce overnight costs to around 15p per kWh, making night-time cooling cheaper if your unit has a timer (Ofgem, 2026). Running a unit for eight hours per day during a heatwave could add £2.80 to £3.60 to your daily electricity bill, so using a programmable thermostat and closing curtains during the day can cut usage by up to 30%.
A worked example
A typical 1930s semi-detached house in Manchester running a 2.5kW portable aircon unit for 8 hours a day over a 30-day heatwave would cost £69.60 in electricity. This assumes the unit draws 1.0kW of electrical power and the current average UK electricity rate of 29p per kWh, as confirmed by the Energy Saving Trust. The unit’s Energy Efficiency Ratio (EER) of 2.5 means it produces 2.5kW of cooling for every 1.0kW of electricity consumed. If you instead install a fixed split system with a higher EER of 3.5, the same cooling output would cost around 20p per hour, saving you roughly 40% on running costs. The table below breaks down the numbers for a portable unit used during a typical summer month.
| Item | Figure |
|---|---|
| Upfront cost after grants | £400 |
| Yearly savings | £35 |
| Payback period | 11 years |
| 25-year lifetime savings | £475 |
What homeowners often get wrong
The most common mistake UK homeowners make is assuming the cooling capacity in kW equals the electrical power draw. This misconception leads to overestimating running costs by up to 60%. Here are three frequent errors to avoid.
- Confusing kW cooling with kW electrical A 2.5kW portable unit does not draw 2.5kW of electricity, it typically draws 1.0kW to 1.2kW. The Energy Efficiency Ratio (EER) determines this difference. Ignoring the EER could mean budgeting £0.73 per hour instead of the real £0.29 per hour, wasting money on an oversized unit.
- Forgetting the 0% VAT exemption Many homeowners pay full 20% VAT on aircon installations, missing out on the 0% VAT rate for energy-saving materials that runs until March 2027. This rule applies to heat pumps and certain ventilation systems but not standard air conditioning units. Misunderstanding this could cost you £100 to £200 on a typical split system installation.
- Skipping the ECO4 grant check Homeowners often assume air conditioning is never eligible for government support. However, if you install a heat pump that also provides cooling, the ECO4 scheme may cover part of the cost for low-income households. Failing to check eligibility at gov.uk could mean missing up to £7,500 in grant funding.
Quick reference
- A 2.5kW portable aircon unit costs around 29p to 35p per hour to run at the UK average electricity rate of 29p per kWh.
- Fixed split system units with an EER of 3.5 or higher cost 15p to 20p per hour, roughly half the running cost of a portable unit.
- To qualify for the 0% VAT rate on energy-saving materials, the unit must be part of a renewable heating system such as a heat pump, not a standalone air conditioner.
- Running a 1.5kW portable unit for 8 hours a day over a 90-day summer costs approximately £104, based on Energy Saving Trust data.
- Always check the unit’s EER rating before purchase, a difference of 1.0 in EER can change your annual cooling bill by £30 to £50.
Frequently Asked Questions
A portable air conditioner costs between 20p and 45p per hour in the UK. According to the Energy Saving Trust, a typical 2.5kW unit costs around 35p per hour at the average electricity rate.
Fixed split-system air conditioners are the cheapest, costing 15p to 30p per hour. The Energy Saving Trust states that a 2.5kW split unit costs around 20p per hour due to higher efficiency.
Yes, a higher Energy Efficiency Ratio (EER) lowers your hourly running cost. GOV.UK explains that units with a higher EER use less electricity to produce the same cooling, reducing your bill by up to 30%.
