The short answer
Around 23–25°C for cooling and 20–22°C for heating are sensible starting points, adjusted a degree at a time to suit you. A setting far lower or higher than you want won't get the room there much faster.
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The number on the remote is a target for the air around the indoor unit, not a promise for every corner of the room. How comfortable a setting feels depends on the humidity, the sunshine, what you're wearing and what you're doing, so treat any figure as a place to start.
Good starting points
| Situation | Starting point | Notes |
|---|---|---|
| Cooling during the day | 23–25°C | Go up a degree if it feels chilly |
| Cooling a bedroom at night | Your daytime setting, with sleep mode | Sleep mode eases it up overnight |
| Heating during the day | 20–22°C | The unit's sensor sits high up |
| Heating overnight | A few degrees lower | Or off, if the room holds its heat |
| Away in winter | Off, or frost protection | Frost protection is on some models |
Change the setting a degree at a time and give the room a while to settle, often half an hour or so, before changing it again. Once you've found what suits a room in each season, you can mostly leave it there.
If you have units in several rooms, each can have its own setting. A bedroom is often set differently at night, and a room that catches the afternoon sun may need a lower setting later in the day. At night, sleep mode adjusts the setting gradually for you.
Why a lower setting isn't faster
When a room is well above your setting, the system is already working at or near full output. Setting 18°C instead of 24°C won't make it cool much faster. It just keeps cooling past the point you wanted, so you end up too cold and the system uses more electricity getting there.
The same applies to heating. Turning the setting up to 28°C on a cold morning won't warm the room much faster than 21°C would. If you want a quick change, use the powerful function if your model has one, then let it return to normal.
Why the room and the setting can differ
The unit measures the temperature of the air it draws in, high on the wall. Several things mean that reading won't always match how the room feels where you are.
- Warm air rises. When heating, warmth collects near the ceiling, so the unit can decide the room is warm enough while it still feels cool at chair height. Pointing the airflow down helps (see directing the airflow), and you may need a degree or two more than you'd set on a central heating thermostat.
- Cool air sinks. When cooling, the air near the floor can be colder than the setting.
- Sunshine and warm surfaces. Sun on your skin, or on a sofa by a window, can make a room feel warmer than the air temperature suggests.
- People and equipment. Computers, televisions, cooking and a room full of people all add heat.
Some remotes, wall controllers and apps can use a temperature sensor where you are instead of the one in the indoor unit. Your manual will say whether yours can.
Humidity changes how warm it feels
Damp air feels warmer than dry air at the same temperature, because sweat evaporates from your skin more slowly. Cooling takes moisture out of the air as well as heat, so once a room has dried out you may be comfortable a degree or so higher than you expected.
On days that are muggy but not especially hot, dry mode may suit you better than cool. There's more in humidity and comfort.
The setting and your electricity use
The further your setting is from the temperature outside, the more heat the system has to move and the more electricity it uses. That doesn't mean putting up with discomfort. It does mean the best setting is usually the warmest one you're happy with in summer and the coolest one you're happy with in winter, rather than a fixed number kept out of habit.
A big gap between indoors and out also makes stepping outside on a hot day feel harsher. For more ways to keep electricity use down, see how to cut running costs.
Related guides
- The modes explained: cool, heat, dry, fan and autoCool lowers the temperature and takes out some moisture, heat warms the room, dry mainly removes moisture with gentle cooling, fan only moves air, and auto chooses between cooling and heating for you.
- Humidity and comfortHumidity changes how warm a room feels at the same temperature. Most people are comfortable with relative humidity of roughly 40–60%; above that, warm rooms feel close and sticky, and air conditioning helps by taking moisture out as it cools.
- How to cut running costsSet 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.
- Sleep and quiet modesSleep mode usually shifts your setting by a degree or two over the first hours of the night, warmer when cooling and cooler when heating, and turns the fan down. Quiet mode slows the fan to cut noise, at the cost of some output.