The short answer
The cheapest way to run air con is to size the unit correctly, set a moderate temperature, run it only when you need real cooling, keep doors and windows shut, shade the room and clean the filters. Each of these reduces the power the unit draws — and since cost is power drawn times hours times your unit rate, cutting any of those three factors cuts the bill. A well-maintained inverter unit, used sensibly, stays around 15–25p per hour.
Running cost comes down to one equation: power drawn multiplied by hours multiplied by your unit rate. So the cheapest way to run air conditioning is simply to reduce one or more of those three. This page sets out the practical, Energy Saving Trust-aligned habits that do exactly that, without sacrificing the comfort you bought the system for.
Cheapest running at a glance
- Cost formula Power × hours × unit rate
- Set temperature Moderate, not extreme
- Run time Only when real cooling is needed
- Maintenance Clean filters, keep coils clear
- Biggest saving Correct sizing from the start
Start with the right unit
The cheapest running cost is decided before the unit is even switched on. An oversized unit short-cycles and wastes power; an undersized one runs flat out and never coasts into its efficient range. A higher energy-rating model draws less electricity for the same cooling, lowering every single hour of its working life. Getting the sizing and efficiency right at the point of purchase is the single biggest lever on lifetime cost, and it is a decision you only get to make once — so it is worth a proper survey. See what size do I need and most energy-efficient air con.
- Size the unit to the room, not bigger “to be safe”.
- Choose a high energy-rating model.
- Prefer an efficient inverter over a basic on/off unit.
Settings that cut the bill
Once installed, your settings do most of the work. Every degree lower you set the thermostat makes the unit work harder, so a moderate target temperature is far cheaper than a fridge-cold one. Run the unit only when you genuinely need cooling rather than around the clock. Use timers or eco modes to avoid cooling an empty room or to ease off overnight. Because cost scales directly with hours and with how hard the unit works, these habits translate straight into a lower bill — no new hardware required.
| Habit | Why it saves |
|---|---|
| Moderate set temperature | Less power drawn per hour |
| Run only when needed | Fewer hours on the meter |
| Timers / eco mode | Avoids cooling an empty room |
| Doors and windows shut | Stops cooled air escaping |
Keep the heat out and the unit clean
The less heat enters the room, the less the unit has to remove. Closing windows and doors while it runs, drawing blinds or curtains against direct sun, and improving insulation all reduce the cooling load and therefore the power drawn. Equally, a clogged filter or a blocked outdoor unit forces the system to work harder, so regular filter cleaning and keeping the condenser clear of leaves and debris directly lower running cost. The Energy Saving Trust’s general advice — maintain the appliance, reduce the load — applies precisely here, and most of it is free.
- Shut windows and doors while cooling.
- Shade the room from direct sun with blinds or curtains.
- Clean filters regularly and keep the outdoor unit clear.
Use it selectively
The cheapest air con is often the one you use sparingly. Pair it with a fan on milder days, reserve it for the hottest spells, and keep up the annual service so it stays efficient and does not quietly start drawing more power than it should. Done this way, a 2.5 kW split sits around 15–25p per hour rather than spiralling into a bill shock. The habits compound: a right-sized, well-maintained unit set to a moderate temperature and run only when needed is dramatically cheaper than the opposite on every count. For the numbers see running cost and the per-hour view in cost to run air con per hour.
The order that saves the most
If you tackle the cost levers in the right order, the savings compound. Start at purchase, because correct sizing and a high energy rating set a low floor under every hour the unit will ever run — no amount of careful use can fully undo an oversized or inefficient unit. Next come the settings, which you control daily: a moderate target temperature and running the unit only when needed are free and immediate. Then comes reducing the cooling load — shutting windows, shading the room, improving insulation — so the unit has less work to do in the first place. Finally, keep it maintained, so it never quietly starts drawing more power than it should through a dirty filter or a developing fault. Hardware, settings, load and maintenance, in that order: each step multiplies the benefit of the last, and together they keep a 2.5 kW split firmly in the 15–25p-per-hour range rather than letting the cost drift upward.
These are typical 2026 estimates and general efficiency advice, not a guarantee for your home. Your real cost depends on your unit, your tariff and your habits.
Spend less, stay comfortable
Size the unit right, set a moderate temperature, run it only when needed and keep it maintained — that is how running cost stays low.
Frequently asked questions
What is the cheapest temperature to set air con?
A moderate target rather than an extreme one. Every degree lower forces the unit to draw more power, so a comfortable, moderate setting is the cheapest that still keeps you cool.
Is it cheaper to run air con on a timer?
Yes, if it stops the unit cooling an empty room. Timers and eco modes cut the hours on the meter, and cost scales directly with hours run.
Does cleaning the filter really save money?
Yes. A clogged filter restricts airflow and makes the unit work harder, drawing more power. Regular filter cleaning keeps it efficient — and it is a task you can do yourself.
Is a portable a cheaper way to run air con?
Not usually. Portables are typically less efficient than fixed splits, so they often cost more per hour for the same cooling, even though they are cheaper to buy.
Sources & further reading
- Energy Saving Trust — efficiency and running cost guidance
- Ofgem — typical domestic electricity unit rates
- Manufacturer technical data (e.g. Daikin, Mitsubishi Electric) — power input and efficiency specifications
- gov.uk — household energy efficiency information
This guide is general information, not a site-specific survey or a substitute for a quote from an F-Gas-certified installer. Installation, servicing and refrigerant handling are legally restricted to F-Gas-certified engineers.