In the final days of May, temperatures in Vietnam’s two largest cities, Hanoi and Ho Chi Minh City, have remained around 40 C. In Hanoi, where humidity has hovered near 80%, weather applications have reported "feels like" temperatures of 45-50 C.

The intense heat and direct sunlight have caused air conditioners to operate at maximum capacity for extended periods, yet many units still struggle to cool rooms effectively. The strain increases electricity consumption, reduces the lifespan of the equipment and can also affect human health.

Below are several recommendations for using air conditioners more effectively during severe heatwaves.

Set temperatures at 26-28 C

Manufacturers generally recommend setting air conditioners at temperatures 7-10 C lower than outdoor conditions. However, when outdoor temperatures exceed 40 C, experts advise keeping units at 26-28 C to balance cooling comfort and operating efficiency.

Lower settings, such as 16-20 C, force air conditioners to run continuously at maximum power, increasing the risk of overload and mechanical damage. Experts say most residential air conditioners commonly used in Vietnam cannot realistically cool rooms to around 20 C when outdoor temperatures remain above 40 C.

Keeping temperatures at 26-28 C also helps reduce the risk of heat shock when moving between heavily air-conditioned spaces and extreme outdoor heat.

A weather app on a smartphone shows an outdoor temperature of 41 degrees Celsius in Hanoi at noon on May 25, 2026 with a real-feel temperature of 47 C. Photo by VnExpress/Tuan Hung

Combine fans with AC

Before turning on the air conditioner, users can open windows and run fans for around 15 minutes to push hot air out of the room. Fans should continue operating at lower speeds while the air conditioner is on to help distribute cool air more evenly.

The combination can reduce pressure on the air conditioner and improve cooling efficiency during extreme heat.

Avoid running AC all day

Even during prolonged heatwaves, users are advised to give air conditioners short breaks after every four to six hours of operation.

Turning the unit off for about an hour and opening windows to ventilate the room before restarting it can help extend the system’s lifespan and reduce strain on the equipment.

Reduce heat entering the room

Apartments with large glass surfaces often absorb and retain more heat, forcing air conditioners to work harder and consume more electricity.

Experts recommend installing thick light-blocking curtains and keeping them closed during the day, especially in apartments exposed to direct sunlight.

Heat-insulating window films similar to those used on cars can also help block heat and ultraviolet rays.

Shield outdoor units

Outdoor condenser units are designed to operate outside but still perform better in well-ventilated areas protected from prolonged direct sunlight.

Users can install covers or mesh shields above the units, though care should be taken not to block airflow from the cooling fan.

Clean AC regularly

Dust and dirt can build up inside air conditioners after relatively short periods of use, reducing cooling performance and increasing electricity consumption.

Experts recommend cleaning both indoor and outdoor units at least once every six months to maintain efficient operation.