How Long Should You Keep the Air Conditioner On When Leaving a Room? Taipower Reveals 'Never Turn It Off Before This Time' and One Trick to Save on Electricity Bills All Day

As scorching summer heat continues, many households keep their air conditioners running almost all day. However, when stepping out briefly, people often wonder whether to leave the AC on or turn it off to save electricity. A netizen recently posted on Dcard under the title '2026 Air Conditioning Energy-Saving Guide,' asking, 'Should I turn off the AC when going out for three hours?' Opinions were divided: some argued that frequently turning an inverter AC on and off consumes more power, so it's better to keep it running; others believed that leaving the AC on for hours in an empty house simply wastes electricity and increases bills.

In response, Taiwan Power Company (Taipower) has provided clear guidance. The key benchmark isn't three hours—it's 30 minutes. In its 'Electricity Consultation Room' summer energy-saving tips, Taipower explains that for inverter air conditioners, if you're leaving for less than 30 minutes, it's better to keep the unit running rather than turning it off. This is because once the room reaches the set temperature, the compressor operates at a low frequency, consuming relatively little power. In contrast, frequently restarting the AC requires higher power output each time, which may actually increase energy consumption.

However, if you're leaving for more than three hours, this no longer qualifies as a 'brief absence,' and Taipower recommends turning the AC off. Don't assume that keeping the AC running all day is always more energy-efficient.

Moreover, AC power consumption isn't solely determined by on/off timing—it's also significantly affected by housing conditions. Factors include the AC model, room size, building insulation, floor level, and whether the room receives direct afternoon sunlight (west-facing exposure). West-facing rooms tend to accumulate heat in the afternoon, making it harder to cool down upon return. However, leaving the AC running for hours while no one is home isn't necessarily more cost-effective.

Before leaving, close curtains, thermal curtains, or blinds, and ensure all windows and doors are tightly shut to reduce indoor heat absorption. This helps lower cooling demands when you return. If your household includes elderly members, infants, or pets sensitive to temperature changes, prioritize health and safety over electricity savings when deciding whether to keep the AC on.

In addition, Taipower shares three key energy-saving tips for air conditioning: First, set the temperature between 26°C and 28°C. For every 1°C increase, you can save about 6% on cooling electricity. Second, use a circulator fan or electric fan alongside the AC to accelerate cold air circulation and improve cooling efficiency. Third, clean the AC filter every two to three weeks. Dust buildup reduces heat dissipation and forces the unit to work harder, leading to unnecessary power consumption. Regular maintenance ensures optimal performance.

Source: Taipower Editor: Tsai Hui-Hsin