Should you turn off the AC when leaving? How to avoid a power bill shock this summer
Shoppers look at air conditioners on display in an appliance store in Yongsan District in central Seoul in this file photo. Yonhap
With record-breaking heat gripping the country, air conditioner use has surged in households — and so have concerns about soaring electricity bills. On social media, various “power-saving tips” have gone viral, such as “It’s better to leave the AC running than turning it on and off” or “Use dehumidifying mode instead of cooling.”
While energy experts caution that there's no one-size-fits-all answer — since factors like temperature, humidity, and floor layout vary — they largely agree on one thing: If you’re stepping out for a short time, don’t turn off the AC.
'Don't turn it off for short outings — it's the inverter system'
According to a 2023 article from Samsung Electronics’ newsroom titled “Tips from developers on maximizing air conditioner energy efficiency,” researchers at Samsung’s Air Solution Technology Lab conducted real-world experiments to assess energy use. They found that if you’re leaving for less than 90 minutes, keeping the AC on is more efficient. In contrast, if you’re gone for longer, it’s better to turn it off and restart it upon returning.
The researchers explained that restarting the AC after a 30-minute absence led to 5 percent more energy use compared to continuous operation. For 60-minute absences, it was 2 percent more. But if the outing exceeded 90 minutes, turning off the unit saved more electricity overall.
This is due to the characteristics of inverter-type air conditioners, now standard in most homes. These systems adjust the compressor speed once the target indoor temperature is reached, allowing the outdoor unit — the main source of energy consumption, accounting for 90 to 95 percent of the AC’s electricity use — to operate at a lower output.
Samsung said, “If you turn off an inverter air conditioner for a short time, it will consume more power to cool the room again when restarted.”
'Turn it off if you have an older, non-inverter model'
Older non-inverter (fixed-speed) air conditioners work differently: they run at full power until reaching the target temperature, then completely stop. When the temperature rises again, the system restarts at full output. As a result, leaving them on during outings leads to higher power consumption. For these models, it’s more efficient to turn them off once the room is cool.
As for the common belief that using dehumidifying mode saves electricity, manufacturers say the difference is negligible. A 2023 study by the Korea Consumer Agency tested five household stand-type AC models from Samsung, LG, and Carrier. When operated at 24 degrees Celsius for five hours, the average power consumption was 1.782 kWh in cooling mode and 1.878 kWh in dehumidifying mode — showing no significant savings and even slightly higher consumption in dehumidifying mode.
This article from the Hankook Ilbo, the sister publication of The Korea Times, is translated by a generative AI system and edited by The Korea Times.