Air conditioning during a heatwave: what temperature is recommended in the bedroom at night

During heatwaves, more and more people are leaving their air conditioning units running through the night. Doctors warn that it is not just a matter of whether the unit is in use, but also the temperature it is set to, as large differences compared to the heat outside can cause discomfort.

What temperature is recommended in the bedroom

Dr. Răzvan Lungu, a pulmonologist certified in sleep medicine, explains to Digi24.ro that in summer the bedroom temperature should generally be kept between 18 and 20 degrees Celsius. The optimal value may vary from person to person, depending on how well they have adapted to the heat and their individual preferences, but it is important that the temperature in the home does not exceed 24 degrees Celsius at night. When it is too warm, the body is unable to regulate its core temperature naturally, and sleep becomes lighter and more frequently disturbed.

The doctor also recommends avoiding large temperature differences between outdoors and indoors. On days when temperatures exceed 35 degrees Celsius, the home should be cooled gradually: the unit should initially be set to 25–26 degrees, then the temperature reduced gradually to a comfortable level, in order to prevent the discomfort caused by sudden changes.

Is it safe to sleep with the air conditioning on all night?

According to the same specialist, using the unit overnight does not pose a major health risk, provided it is used correctly. The flow of cool air should not be directed straight at the bed, and prolonged exposure to strong draughts should be avoided. If the unit is properly installed and operating at a moderate temperature, the risks are minimal.

The doctor emphasises that during very hot periods, air conditioning can help maintain an environment conducive to rest and can prevent the effects of overheating on the body. In his view, the discomfort associated with air conditioning is often overstated, whilst the negative effects of prolonged exposure to excessive heat on sleep and on various health conditions are far more significant.

Why heat affects sleep and health

Dr. Andreea Mihaela Popa, a pulmonologist, explains to Digi24.ro that under normal circumstances, before falling asleep the body slightly lowers its core temperature — an essential process for the onset of sleep. If the bedroom is too warm, shedding excess heat becomes more difficult, which can delay the onset of sleep and reduce the quality of rest.

On sweltering nights, sleep becomes lighter, with frequent wakening, and the deep sleep stages (N3) and REM sleep are particularly affected — both of which are essential for physical recovery, memory consolidation, and healthy cognitive and emotional functioning. Even if the total number of hours slept appears sufficient, the rest is less restorative, and the following day may bring fatigue, drowsiness, difficulty concentrating, irritability, and reduced physical and intellectual performance.

The doctor notes that numerous studies, as well as the recommendations of the American Academy of Sleep Medicine (AASM) and the European Sleep Research Society (ESRS), show that the temperature of the room in which we sleep is one of the most important factors influencing sleep quality.