Running cost is calculated from electricity consumed, not the unit's cooling output. For example, a system averaging 0.6 kW of electrical input over six hours uses about 3.6 kWh. At an illustrative July 2026 tariff of 25 pence per kWh, that would cost about 90 pence for the period. This is an example, not a forecast: actual input varies as inverter systems modulate, and tariffs, weather, set points, insulation and room heat gains differ.
Use the right calculation
Multiply average electrical input in kilowatts by operating hours, then multiply the resulting kilowatt-hours by your electricity unit rate. Use the rate on your current bill, including VAT where appropriate, rather than an old national average.
Do not use the headline cooling capacity as though it were electricity demand. A unit providing 2.5 kW of cooling may draw much less than 2.5 kW electrically, and an inverter usually changes its input as conditions change.
- Energy used: average electrical input in kW multiplied by hours.
- Cost: energy used in kWh multiplied by tariff in pounds per kWh.
- Add standing charges only when comparing whole household bills, since they are usually payable regardless of air conditioning use.
Why actual use varies
The system may draw heavily while pulling a hot room down to temperature, then reduce output as it maintains the set point. Solar gain, open doors, ventilation, occupants and appliances can keep the load high.
A very low set temperature usually increases consumption. Shading, closing windows while cooling and using sensible schedules can reduce waste without compromising comfort.
Reading efficiency information
Product labels and datasheets may show seasonal efficiency values for cooling and heating. These help compare equipment under standard test assumptions, but they cannot predict a particular home's bill.
For reversible air-to-air heat pumps, heating performance should be considered separately from cooling. Their heating may displace another fuel or electric heater, so annual cost comparisons need the price and efficiency of the alternative.
Create a cautious annual estimate
Build low, central and high scenarios using plausible hours, average input and your tariff. Record the date of the tariff because energy prices change. A plug-in monitor cannot usually measure a hard-wired split system, but some units or electrical monitors provide consumption data.
Maintenance affects performance. Clean filters as instructed and keep outdoor airflow clear. A sudden rise in consumption or fall in output should be investigated rather than assumed to be normal ageing.
Frequently asked questions
How much does air conditioning cost per hour?
There is no fixed figure. Multiply the unit's average electrical input by your tariff. At 25 pence per kWh, an average 0.5 kW input costs about 12.5 pence per hour, while 1 kW costs about 25 pence.
Does an inverter always run at full power?
No. It generally varies compressor speed to match demand, although it may run near maximum during initial pull-down or extreme conditions.
Is leaving air conditioning on cheaper than switching it off?
Not as a universal rule. Maintaining an empty room at a large temperature difference wastes energy. Timers, occupancy controls and moderate set points are usually more useful than blanket advice.
Can a reversible system reduce heating bills?
It can be cheaper than direct electric resistance heating in suitable conditions, but savings against gas or other systems depend on tariffs, efficiencies, heat demand and how the home is used.
Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.