How Much Does Air Conditioning Cost to Run? Prices and Factors

The cost of running air conditioning is the electricity it uses multiplied by the price you pay for that electricity. For a modern inverter split system cooling a single room, it's usually far less than people expect. That's because the unit's electrical input is only a fraction of its cooling output. Your own figure, though, depends on the system, the rooms, how you use it and your tariff. Any number we quoted here probably wouldn't match your bill, so this guide shows you how to calculate it yourself.

We start with the basic formula and the difference between cooling capacity and power use. Then we explain SEER and SCOP, go through some worked examples at a clearly labelled example rate, and finish with what pushes running costs up or down.

The basic running cost formula

Every running-cost calculation for an air conditioner follows the same three steps:

1. Electrical input (kW). How much electricity the unit draws while running. Note that this is the input power, not the cooling capacity printed on the box.
2. Hours of use. Multiply input by hours to get kilowatt-hours (kWh), the unit your supplier bills you in.
3. Your unit rate (p/kWh). Multiply kWh by the unit rate on your electricity bill to get the cost in pence.

Running cost (pence) = electrical input (kW) × hours of use × unit rate (p/kWh)

Leave your standing charge out, as it doesn't change when you use air conditioning. On a time-of-use tariff, use whichever rate applies to the hours the unit actually runs.

Cooling capacity is not the same as power use

This trips up more people than anything else. A "3.5kW air conditioner" describes how much heat it can remove from a room. It says nothing about how much electricity it consumes. A split system is a heat pump, so it moves heat instead of creating cold, and it typically shifts several kilowatts of heat for every kilowatt of electricity it uses.

As an illustration, a 3.5kW unit might draw somewhere around 1kW of electricity when running flat out on a hot afternoon. Once the room has reached temperature and the inverter compressor slows down, it draws considerably less. You'll find the real figures for any model on its specification sheet, listed as rated power input in cooling and heating.

Two further points follow from this:

• Air conditioners rarely run at full output for long. An inverter unit spends most of its time at part load, which is where it is most efficient.
• Comparing two units by their cooling capacity alone tells you nothing about running costs. You need their efficiency ratings.

What SEER and SCOP mean on the energy label

UK energy labels for split air conditioners show two seasonal efficiency figures. Both are ratios, and higher is better.

Seasonal figures tell you more than single-point ratings (EER and COP), because they allow for the unit running at part load across a range of outdoor temperatures. They're measured under standard test conditions, so your own results will differ. Even so, they are the fairest way to compare two models.

You can use SEER to estimate running cost from the cooling you need, by dividing the cooling energy by SEER to get the electricity used. Most people find the electrical input method above easier, though.

Worked examples at an example rate

The examples below use an example unit rate of 25p per kWh. This is for illustration only and is not a current tariff. Swap in the unit rate from your own electricity bill. The average input figures are illustrative too, so check the specification of your actual unit.

A summer of bedroom cooling

Say you run a 2.5kW bedroom unit for 6 hours a night on 60 nights over the summer, with an average input of 0.5kW. That's 0.5 × 6 × 60 = 180kWh. At the example rate of 25p/kWh, the season costs 180 × 25p = £45. For your own figure, just multiply 180kWh by your p/kWh rate.

Using it for heating instead

Suppose a room needs 10kWh of heat on a cold day. A plug-in electric heater turns electricity into heat one-for-one, so it uses 10kWh, which is £2.50 at the example rate. A split system with a SCOP of 4 would use roughly 2.5kWh for the same heat (about 62.5p at the example rate). Real-world performance drops in very cold weather, but the gap is still big. Does it beat gas central heating? That depends on your gas and electricity unit rates and how efficient your boiler is, so run the numbers with your own tariff.

What pushes the bill up or down

The right size of system

A unit matched to the room's heat load runs smoothly at part load, which is where inverters are most efficient. An undersized unit runs flat out for hours. An oversized one cycles on and off and deals with humidity poorly. Our guide to what size air conditioning unit you need explains how sizing is worked out.

How much heat gets in

Big south- or west-facing windows and rooflights let in heat the system then has to remove. Poor loft insulation and thin walls do the same. Blinds, external shading, solar film and better insulation all cut the load before the air conditioner even switches on.

Your set temperature

Every degree cooler you ask for means more work. A setting of 22 to 24°C is usually comfortable in summer and noticeably cheaper than 18°C. Cooling a room to just a few degrees below the outside temperature often feels better than chilling it.

How and when it runs

Running a unit in an empty room wastes energy, and so does leaving the windows open. Cooling the whole house when only one room is in use is another common one, and it's where a zoned multi-split system helps, since each room has its own controller. Timers, schedules and app control let you cool rooms only when someone is in them.

Condition of the system

Blocked filters and dirty coils restrict airflow, so the compressor has to work harder for the same result. A refrigerant leak cuts both capacity and efficiency. Regular filter cleaning and an annual service keep the system close to its rated efficiency. Our air conditioning maintenance article covers what a service involves.

Age and type of equipment

Older fixed-speed units, and systems still running on R22, are much less efficient than modern inverter splits on R32. R22 can no longer be used to service systems either, so repairs get difficult. Replacement often pays for itself partly through lower running costs, and the engineers at UK Aircon can talk you through it alongside our air conditioning repair service.

Portable units versus fixed split systems

Portable air conditioners look cheap to buy, but per unit of cooling they're among the most expensive ways to cool a room. They draw a lot of electricity. The hot exhaust hose also runs out through a window, so warm outside air leaks back in around the gap. Single-hose models make it worse by pulling replacement air into the room from outside or from elsewhere in the house.

A fixed split keeps its compressor outside the building, which avoids both problems. It runs far more quietly and gives you efficient heating in winter too. If you're comparing the two, plug each unit's electrical input into the same formula, then judge the result against how well each one actually holds the room temperature.

Practical ways to keep costs down

• Close doors and windows while cooling
• Draw blinds on sunny glazing
• Set 22 to 24°C in summer
• Use timers in place of all-day running
• Clean filters every few weeks in heavy use
• Book an annual service
• Keep the outdoor unit clear of debris
• Use eco or night modes where available

Businesses with larger systems carry extra obligations, and these help efficiency too. Systems over 12kW need a TM44 energy inspection every five years, which often turns up settings and control changes that reduce consumption. Our commercial air conditioning article goes into this in more depth.

Finding your own numbers

For a realistic running cost, you need three things. First, the rated power input from your unit's specification sheet, or the energy monitor in its app if it has one. Second, a rough idea of how many hours you'll run it. Third, the unit rate from your latest electricity bill. A smart meter's in-home display can also show the jump in consumption when the system kicks in. Put those into the formula and you'll have a figure based on your own tariff rather than someone else's average.

Running cost FAQs

Lower running costs start with the right installation

Low running costs start with an efficient system that is correctly sized, well positioned and properly commissioned. UK Aircon's REFCOM-registered engineers recommend systems with strong SEER and SCOP ratings and size them on a proper survey. Explore our domestic air conditioning installation service, with installs from £1,800, or get a free quote and we will reply within 24 hours.