Air conditioning running costs

Most people asking what air conditioning costs to run are worried about the wrong season. Cooling a UK home is cheap — a bedroom unit through a hot summer costs less than a few takeaways. What actually moves your bill is using the same unit for heating in winter, and that is also where it can save you a great deal of money against an electric heater. This page works both numbers from the current price cap so you can see the difference rather than take it on trust.

Start with the number that does the work

Running cost is output divided by efficiency, multiplied by your unit rate. The unit rate is the part you can look up.

Under the Ofgem price cap for 1 October to 31 December 2026, the Great Britain average electricity unit rate for a Direct Debit customer on a single rate is 26.32p per kWh [1]. It varies by region rather more than people assume:

Source: Ofgem price cap, Direct Debit, single rate [1]. The cap is reset every three months, and it applies to standard variable tariffs — not to fixed tariffs, business contracts or heat networks [2].

That spread is a real 2.5p between the cheapest and most expensive regions, which is roughly a 10% difference on every calculation below. Use your own region's figure if you want a number you can hold your installer to.

The cooling number: smaller than you expect

Take a typical bedroom or home office split system rated at 2.5kW of cooling output, with a SEER of 8.5 — an ordinary figure for a current inverter unit, not a flagship.

Run it six hours an evening across sixty hot days:

• Cooling delivered, if it ran at full output the whole time: 2.5kW × 6h × 60 days = 900 kWh. In practice a unit never does this — it modulates down once the room is at temperature — so treat 900 kWh as a hard upper bound.
• Electricity used: 900 ÷ 8.5 = 106 kWh
• Cost at 26.32p: about £28 for the entire summer

That is the ceiling, not the expectation. A correctly sized unit pulls the room down in twenty minutes and then idles at a fraction of full draw, so real figures for evening-only bedroom use commonly land well below that. Even taken at its worst, summer cooling is not what makes an electricity bill hurt.

This is why "is air conditioning expensive to run?" gets a different answer in the UK than in Texas. Our cooling season is short, our nights are cool, and a modulating inverter unit spends most of its life at part load.

The heating number: where the money actually is

The same unit reversed is an air-to-air heat pump. It moves heat instead of generating it, so it delivers several units of warmth per unit of electricity [3]. That changes the arithmetic completely — in both directions.

Take the same 2.5kW unit at a SCOP of 4.5, heating a room five hours a day from October to March:

Same warmth in the room. A difference of about £460 over one heating season, because a resistance heater can only ever return one unit of heat per unit of electricity, while the heat pump returns roughly four and a half.

Two honest caveats. SCOP is a seasonal laboratory average, and a real installation in a draughty room with a badly placed unit will not achieve it. And this comparison is against direct electric heating, which is the relevant benchmark for a room with no wet radiator — a loft conversion, a garden room, a converted garage. Against an efficient gas boiler the picture is closer and depends on the gas and electricity rates on the day.

Notice which number is larger. Winter heating on this example costs nearly five times what summer cooling does. If you are budgeting, budget for the heating.

What moves your figure up or down

The arithmetic above has three inputs. Every real-world variable acts on one of them.

Output required — the load. This is the biggest lever and the one set before you buy anything. Room size, glazing area and orientation, insulation, and how many people and machines are in the room. A south or west-facing room with large glazing can need twice the capacity of a north-facing room of identical floor area, and it will run for longer to hold temperature. Reducing the load with shading, blinds or loft insulation cuts running cost as effectively as buying a better unit — often more cheaply. A conservatory is the extreme case.

Efficiency — SEER and SCOP. SEER is the seasonal cooling figure, SCOP its heating equivalent, and both average performance across a realistic range of conditions rather than one flattering test point. Current units run from around SEER 6 at the budget end to above SEER 9 at the top. On the cooling example above, moving from SEER 6 to SEER 9 changes a £39 summer into a £26 one — real, but small. On the heating example, moving from SCOP 3.5 to SCOP 4.5 saves about £37 a season. Efficiency matters, but it is a smaller lever than load or runtime.

Runtime — how you use it. Occasional evening use costs a fraction of leaving a system running all day. Sensible set points matter more than people expect: each degree lower in cooling mode increases both the temperature difference the system works against and the hours it runs.

Then there is sizing, which acts on all three at once. An undersized unit runs flat out and never gets there. An oversized unit short-cycles — cooling the air fast, shutting off, restarting — which is both less efficient and worse at removing humidity, so the room feels clammy at the "right" temperature. The room sizing guide covers how a heat-load calculation gets this right.

The maintenance tax on running cost

A neglected system quietly gets more expensive. Dust loading on filters and coils restricts airflow, so the unit runs longer and harder for the same result, and restricted airflow lowers coil temperatures in ways that push the compressor into cycles it was not designed for.

Cleaning filters is a free, ten-minute job you do yourself. Our servicing guide covers the intervals and where the line sits between DIY and an F-Gas engineer.

Working out your own number

The formula is short enough to do on a phone:

(hours of use × kW of output ÷ SEER or SCOP) × your unit rate in £

So a 3.5kW unit at SCOP 4.2, four hours a day, at 26.32p: (4 × 3.5 ÷ 4.2) × 0.2632 = 88p a day.

Three things to collect before you trust any figure an installer gives you:

1. Your regional unit rate from the Ofgem table [1] — not a national average.
2. The SEER and SCOP of the specific model, not the range's headline figure. These are published per model.
3. A heat-load calculation for the actual room, which is what determines the kW figure in the formula.

Our cost estimator works from these, and the installation cost guide covers the upfront side.

Frequently asked questions

How much does air conditioning cost to run per hour in the UK? For a 2.5kW unit at SEER 8.5, running at full output, about 8p an hour at the GB average rate of 26.32p per kWh [1]. Most units modulate below full output for most of their runtime, so the real average is lower.

Is air conditioning expensive to run? For summer cooling in a UK home, no — a bedroom unit through a hot season is a low tens of pounds. Winter heating with the same unit is the larger number, and that is where efficiency is worth paying for.

Is it cheaper than an electric heater? Substantially. On the worked example above, a heat pump at SCOP 4.5 costs about £132 for a heating season against roughly £592 for a resistance heater delivering the same warmth [1][3].

Does the standing charge count? No. You pay it regardless of whether the system runs [1][2], so only the unit rate belongs in the calculation.

Do higher SEER units pay for themselves? Over a UK cooling season alone, rarely — the absolute saving is small. Over the heating season, and across a system's life, a better SCOP is a more convincing case.

Will running it overnight cost a lot? Overnight cooling in the UK is usually cheap, because outdoor temperatures fall and the unit works against a smaller difference. A correctly sized unit on night mode spends most of the night idling.

Get a figure for your actual rooms

Generic numbers only get you so far, because load is the biggest variable and it is specific to your house. Tell us about the rooms and we will match you with one vetted installer who will do the heat-load calculation and quote against it: get an installer match.