Air Conditioning Running Costs UK: What Will It Add to My Bill?

Running a small bedroom air conditioning unit for eight hours overnight costs around 90p, based on the current Ofgem rate of 26.11p per kWh (Q3 2026). A whole-house system running the same hours costs closer to £3.58. Air conditioning running costs UK wide are lower than most buyers assume, and the figures below show exactly how those numbers are built, so you can work out what your own setup would add to your bill rather than guessing.

How much does it cost to run air conditioning per hour?

The cost depends on two things: the unit’s cooling output in kW, and its EER (Energy Efficiency Ratio), which tells you how much cooling it produces per unit of electricity it consumes. Divide the output by the EER and you get the electricity draw. Multiply that by the unit rate and you have your cost per hour.

A typical modern split system has an EER between 3 and 4.5 in normal conditions. Using an EER of 3.5, a small 1.5kW bedroom unit draws around 0.43kW per hour. At 26.11p per kWh, that works out to roughly 11p an hour.

What a typical heatwave week costs

Most UK buyers do not run AC continuously. The realistic pattern is overnight use during a hot spell, so the figure that actually matters is the cost of a heatwave week, not a single hour.

For a small bedroom unit running 8 hours overnight at 11p an hour, that is around 90p a night, or approximately £6.27 across seven nights.

Running costs for different system sizes

The hourly cost scales with the size and number of units running. Three worked examples, all using an EER of 3.5 and the current 26.11p per kWh rate:

Small bedroom unit (1.5kW cooling output)
Electricity draw: approximately 0.43kW per hour
Cost per hour: approximately 11p
Cost for 8 hours overnight: approximately 90p
Cost for a heatwave week: approximately £6.27

Medium living room unit (2.5kW cooling output)
Electricity draw: approximately 0.71kW per hour
Cost per hour: approximately 19p
Cost for 8 hours: approximately £1.49
Cost for a heatwave week: approximately £10.44

Whole-house multi-split (three units, 6kW combined output)
Electricity draw: approximately 1.71kW per hour
Cost per hour: approximately 45p
Cost for 8 hours: approximately £3.58
Cost for a heatwave week: approximately £25.07

These are the numbers to compare against any running cost claim an installer gives you verbally. If a salesperson quotes a much higher figure to push you toward a smaller system, or a much lower one to make a large system sound harmless, ask them to show the EER and output figures behind their claim.

Air-to-air heat pump heating mode: why winter costs are lower than you might expect

If you are considering an air-to-air heat pump rather than a cooling-only unit, the running cost picture changes in winter. In heating mode, the same technology that cools your home in summer delivers heat far more efficiently than a direct electric heater.

A heat pump with a SCOP (Seasonal Coefficient of Performance) of 3.5 produces 3.5kW of heat for every 1kW of electricity it consumes. A direct electric heater produces exactly 1kW of heat per 1kW consumed. Using a 2.5kW heat output as the comparison:

Direct electric heater: 2.5kW consumption, approximately 65p per hour
Air-to-air heat pump (SCOP 3.5): approximately 0.71kW consumption, approximately 19p per hour
Saving versus direct electric heating: approximately 71%

Against gas, the comparison is closer than it is often presented. Using the current Ofgem Q3 2026 gas rate of 7.33p per kWh and a boiler operating at 90% efficiency, gas costs approximately 8.1p per kWh of heat delivered. A heat pump at SCOP 3.5 on the current electricity rate costs approximately 7.5p per kWh of heat. The heat pump is still cheaper, but by around 8%, not by a dramatic margin. Anyone telling you a heat pump will slash your heating bill compared to gas is overstating the case at current tariffs. The real advantage is against direct electric heating, where the saving is genuine and large.

What affects your running costs

Four things move these figures more than anything else:

SCOP and EER rating. A unit with a lower EER or SCOP than the ones used here will cost more to run for the same output. Ask any installer quoting you for the SCOP and EER of the specific unit being proposed, not a generic manufacturer range.

Set temperature. Every degree lower in cooling mode increases consumption. 24°C is a reasonable overnight sleeping temperature. Running at 18°C costs noticeably more to maintain and is rarely necessary for comfort.

Insulation. A well-insulated room holds its temperature and needs less continuous running. A poorly insulated loft conversion or conservatory will cost more to cool than these figures suggest, regardless of unit size.

Outdoor temperature. In a genuine heatwave, above 30°C outside, the unit works harder to maintain the same indoor temperature and consumption rises above these baseline figures.

Annual cost in context

UK heatwaves are not year-round events. A typical homeowner might run a bedroom unit for somewhere between 20 and 40 nights a year under current UK climate patterns. At approximately 90p a night, that is between £18 and £36 a year for one bedroom.

This is the figure most buyers have not actually calculated before getting a quote, and it is usually lower than they expect. If you also use an air-to-air heat pump for winter heating, the annual picture shifts again. A heat pump used regularly through a UK winter will typically save more against direct electric heating than the entire summer cooling cost, even though the saving against gas is modest at current rates.

Final verdict

Cooling costs are not the reason to hesitate on air conditioning. Even a whole-house system run through a full heatwave week costs about the same as a single takeaway order for the household. The number that actually matters for your decision is the installation cost and which system size you need, not the electricity it will draw once it is in. If a heat pump is part of your thinking, treat the gas comparison honestly: it is currently cheaper, but only modestly, and that gap can move with the next quarterly price cap.

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