How Much Does Air Conditioning Cost to Run in the UK?
Real numbers, worked examples and the factors that determine whether your electricity bill goes up by £50 or £500 per year.
The most common question we receive from prospective customers is some version of: 'what will this add to my electricity bill?' The honest answer is: it depends — but we can give you the tools to calculate it accurately for your situation.
The formula
Running cost = system capacity (kW) ÷ COP × hours of use × electricity rate (£/kWh)
A 3.5kW system with a COP of 3.5, running for 500 hours per year (roughly 6 hours per day for 3 months), at 28p/kWh: 3.5 ÷ 3.5 × 500 × 0.28 = £140 per year.
What COP means
COP (Coefficient of Performance) is the efficiency ratio of the system. A COP of 3.5 means the system delivers 3.5kW of cooling or heating output for every 1kW of electrical input. Higher COP means lower running costs.
Typical annual running costs by room size
- •Small bedroom (2.0kW system): £60–120 per year for cooling only
- •Double bedroom or office (3.5kW system): £100–200 per year for cooling only
- •Large lounge (5.0kW system): £150–300 per year for cooling only
- •Including winter heating: add 40–80% to the above figures
These figures assume reasonable use — cooling when it's genuinely hot, not running at maximum power 24/7. If you set a sensible target temperature (22–24°C) rather than trying to cool your room to 18°C in a heatwave, your costs will be at the lower end of these ranges.
Factors that increase running costs
- •Setting a very low target temperature (below 20°C)
- •Poor insulation — heat enters faster than the system can remove it
- •South-facing rooms with large windows and no external shading
- •Running at maximum fan speed continuously
- •Loft conversions and conservatories (high thermal load)
How to reduce running costs
- •Use the timer — pre-cool before you need the room rather than running all day
- •Keep the set temperature at 24°C rather than 20°C — this alone can halve the running cost
- •Close curtains or blinds on the sunny side to reduce solar gain
- •Keep doors and windows closed when the system is running
- •Have the system serviced annually — dirty filters increase energy consumption by 10–20%
The context
Running an air conditioning system for a typical UK summer adds £100–300 to your annual electricity bill for a bedroom or living room. When you consider the alternative — no sleep, lost productivity, dangerous heat for vulnerable family members — most of our customers consider this excellent value.