Timers and schedules

A room takes time to cool down or warm up, and it's easy to leave a unit running in a room nobody is using. Timers deal with both. Remotes, wall controllers and apps set them in different ways, so use your manual for the exact steps.

Types of timer

Countdown timers are usually set in steps of half an hour or an hour, and many let you combine an on timer with an off timer. A light on the indoor unit often shows that a timer is set.

Clock timers and weekly schedules are found on some handheld remotes and on many wall controllers and apps. Many let you set a temperature for each period as well as the on and off times. On some handheld remotes, a clock timer only works if the remote stays where the unit can pick up its signal, and the manual will say whether yours is one of them.

Choosing a start time

How long a room takes to reach your setting depends on the room, the weather and the size of the unit. The simplest way to find out is to note how long yours takes on a typical day, then set the timer to start that long before you need the room.

In summer, starting early helps. Once walls, floors and furniture have soaked up an afternoon of sun, they keep giving that heat back for hours, so a room is easier to keep cool than to cool down. For a room that gets the afternoon sun, a start time before the sun reaches it works better than one timed for your arrival home.

In winter, allow extra time on cold, damp mornings. The outdoor unit may need to pause to defrost, and the indoor fan waits until its coil is warm before blowing, so warming up takes longer than on a mild day.

Schedules in apps and wall controllers

Apps and wall controllers make schedules easier to set and change. Depending on the system, you may be able to:

• set several on and off times a day, with a different temperature for each
• give weekdays and weekends different patterns
• switch the system on from your phone when your plans change
• group several indoor units so they follow one schedule

Check where the schedule is kept. On some systems it runs from the unit or its Wi-Fi adapter and carries on if your broadband drops; on others it relies on an internet connection. Wi-Fi, apps and smart controls covers the options.

Each indoor unit normally has its own timer, so in a home with several units, set each one or use an app that groups them.

Power cuts and clock changes

After a power cut, many units restart in the mode they were running in, but timer settings may be lost. Check them once the power is back.

Clock timers on a handheld remote or wall controller may need adjusting when the clocks go forward or back. Apps usually take the time from the internet, so they change automatically.

Timers, tariffs and solar panels

On a time-of-use tariff, a schedule can move some of the running into the cheaper hours, for example by cooling or heating a room shortly before the price goes up. How well that works depends on your tariff and how long the room holds its temperature. See time-of-use tariffs.

With solar panels, scheduling the system to run while the panels are generating means more of the electricity it uses is generated at home. Sunny afternoons are often when a room most needs cooling, so the two can line up well. There's more in air conditioning and solar panels.

For whether to switch off while you're out or let the system keep going, see leave it on or switch it off.