The short answer
Set a moderate temperature, stop heat getting in (or out, in winter), run the unit only where and when you need it, and keep the filters and outdoor unit clean. Your tariff matters too.
On this page
An air conditioner uses the most electricity on the hottest and coldest days and through the long hours of a heatwave, so changes that trim its work a little every hour add up over a season. Most of them are habits rather than purchases.
Settings
- Choose a moderate temperature. When cooling, the further you pull the room below the temperature outside, the harder the unit works and the less efficiently it runs. Aim for comfortable rather than cold, and when heating, comfortable rather than hot. What temperature to set suggests starting points.
- Don't set it beyond what you want. The unit keeps working until the room reaches the setting, so an extreme setting tends to leave the room colder or warmer than you need.
- Pick the fan speed for comfort. The indoor fan uses little electricity compared with the compressor, so choose the speed that suits you for airflow and noise.
- Try sleep mode. On many units it lets the temperature drift gradually overnight, which means a little less work. How it behaves varies by model.
- Don't let systems fight. Make sure radiators are off in a room you're cooling.
Keep heat where it belongs
When cooling:
- Close blinds or curtains on windows in direct sun. Shading outside the glass, such as awnings or external blinds, stops more heat than blinds inside.
- Keep windows and doors closed while the unit runs, including the door of the room you're cooling.
- Switch off lights, screens and other equipment you're not using, since they all give off heat.
- If it's cooler outside in the evening or early morning, and safe to do so, open windows then and close them again as the day warms up.
When heating:
- Close curtains at dusk and deal with draughts around windows and doors.
- Keep internal doors closed so the heat stays in the room.
Doors, windows and blinds goes into more detail.
When to run it
Run the unit in the rooms you're using, for the hours you need them. A timer or schedule can start it shortly before you get home or go to bed, so it isn't running in an empty room.
Over longer gaps, switching off usually uses less energy. Over short gaps the difference is small either way, because the unit has to work hard to bring the room back to temperature, and it runs less efficiently while it does.
Look after the unit
| Task | How often | Why it helps |
|---|---|---|
| Clean the filters | Every few weeks in regular use | Blocked filters cut airflow |
| Clear the outdoor unit | Whenever leaves or clutter build up | Air must flow freely through its coil |
| Have it serviced | Often yearly, as the manufacturer recommends | Coils, drain and performance get checked |
Keep plants, bins and stored items away from the outdoor unit, and don't enclose it in a way that blocks the airflow. How to clean the filters shows how to do the most frequent job yourself.
Tariffs and choosing a unit
What you pay per kWh matters as much as how many kWh the unit uses. When you review your tariff, compare both the unit rate and the standing charge.
On a time-of-use tariff, moving some of the unit's use into cheaper hours lowers what those kWh cost, as long as the rest of your household's use suits the tariff too. If you have solar panels, running the unit while they're generating uses your own electricity first.
If you haven't chosen a unit yet, two decisions shape its running costs for as long as you have it: size and seasonal efficiency. A unit sized for the room can work steadily rather than flat out or in stops and starts. Higher SEER and SCOP figures on the energy label mean less electricity for the same cooling and heating under the same conditions. A good installer will size the unit from the room itself rather than a rule of thumb.
Related guides
- How much does air conditioning cost to run?Multiply the electricity it uses, in kWh, by your unit rate. How much a unit uses depends on the room, the weather, the temperature you set and its efficiency, so estimate it from its average power draw and the hours it runs.
- Leave it on or switch it off?It depends on how long the room will be empty. For an hour or two the difference is small, so choose on comfort; for a day or longer, switching off or turning the setting back usually means less heat for the system to move.
- Timers and schedulesMost systems have on and off timers that count down a set number of hours, and many controllers and apps add clock times and weekly schedules. Used well, they have a room comfortable when you need it and the system off when you don't.
- Air conditioning and solar panelsSolar panels can supply some or all of an air conditioner's electricity while they're generating, which suits cooling on sunny days far better than heating in winter. Solar electricity you use yourself costs you any export payment you'd otherwise have earned.