Many households consider 26 C the ideal temperature for balancing comfort and efficiency. But Prof. Dr. Nguyen Duc Loi, a former lecturer at Hanoi University of Science and Technology, says this rule mainly applies to older conventional air conditioners that automatically switch off once the set temperature is reached.

Modern inverter air conditioners operate differently. Instead of constantly turning on and off, they run continuously and adjust their output based on the temperature difference between indoors and outdoors.

So, during heat waves, when temperatures reach 40 C, lowering the room temperature to 26 C creates a gap of 14-15 C. This forces the compressor to operate at maximum capacity for extended periods, increasing electricity consumption and potentially shortening the unit’s lifespan.

Keeping the air conditioner fixed at 26°C can cause electricity bills to soar during periods of extreme heat. Photo by Bao Nhien

Thus, he says, the key to saving electricity is not maintaining a fixed setting of 26 C, but minimizing the temperature gap between indoors and outdoors. When temperatures reach 40 C, the air surrounding the outdoor condenser unit can approach 50 C.

Reduced heat dissipation makes the compressor more likely to become overloaded, shut down automatically, or suffer damage if users insist on setting the indoor temperature too low. For this reason, a setting of 27-28 C combined with automatic fan mode is more efficient.

The air circulation helps sweat evaporate faster, making people feel 1-2 C cooler than the actual room temperature.

Cool the room in stages

Rather than keeping the same temperature setting all day, experts recommend adjusting it in stages. After coming indoors from intense heat, users can initially set the air conditioner to 26 C with a high fan speed to cool the room quickly. Once the room reaches a comfortable temperature, the setting should be increased to 27-28 C.

The most energy-intensive phase is the initial cooling period, when the air conditioner is working at full capacity. Raising the temperature slightly after the room has cooled allows the compressor to switch into a maintenance mode that consumes less electricity.

Take advantage of sleep mode

Keeping the temperature at 26 C throughout the night may also affect health, increasing the likelihood of headaches or sore throats.

Because body temperature naturally declines during sleep, the ideal nighttime setting is around 28°C combined with Sleep mode.

When Sleep mode is activated, the air conditioner gradually increases the temperature over time while reducing fan speed. Real measurements suggest that maintaining 28 C in Sleep mode can cut electricity use by up to 50% compared with continuous cooling at 26 C, while also reducing the strain on the compressor.

Temperature settings are only one factor influencing energy consumption. Daily habits such as failing to clean air filters regularly or leaving curtains open can also increase electricity costs.

Some households direct airflow downward, resulting in uneven cooling. Instead, adjusting the louvers to direct air toward the ceiling allows cool air to circulate more evenly throughout the room, improving comfort and efficiency.