This is one of those questions that divides households every summer. One person says to switch it off the moment the room is cool, the other swears that leaving it running costs less. The honest answer: it depends on how long you're away and what kind of unit you have. There's no single rule that works for everyone. Here's how to think it through so the numbers actually add up.
Why there's no fixed answer
An air conditioner uses the most energy when it has to bring a warm room down from scratch. Once it reaches the target temperature, maintaining it costs far less. Switching the unit on and off repeatedly forces it to go through that big startup effort every time. But leaving it running in an empty house for hours is money wasted. The right answer sits somewhere in the middle.
When to leave it on
- Short absences. For an hour or two away, switching off and back on costs more than keeping it running. The room warms up and has to be cooled again.
- If you have an inverter unit. Inverter models slow down on their own once the room reaches temperature and use very little energy to maintain it. They're designed to run for long periods.
- On very hot days. With 35 degrees outside, cooling a baking room back down takes a lot of energy. Better to maintain the temperature.
When to switch it off
- Long absences. Going to work and coming back in the evening? Switch it off. There's no point cooling empty rooms all day.
- Older on-off models. Non-inverter units run at full power or not at all, with no middle ground. Running them for long periods is harder on the electricity bill.
- At night when you can open windows. If the outdoor temperature drops below 24 degrees, opening windows and switching off the unit sometimes works just as well.
The habits that matter more than on or off
The real difference comes from other things. Set the thermostat to 26 degrees instead of 22, because each degree lower adds around 6 percent to your energy consumption. Use the timer to switch the unit on half an hour before you get home instead of running it empty all day. Keep blinds and shutters closed during the sunniest hours so rooms don't heat up. Clean the filters every two or three weeks, because dirty filters use more energy for the same amount of cooling.
The unit you choose changes everything
This whole conversation shifts considerably depending on the technology. With an A+++ inverter air conditioner, the on-or-off question almost disappears, because the unit self-regulates and holds the temperature with minimal consumption. If you're still deciding, that's the best starting point. Browse our low-energy air conditioners and choose based on your room size.