The reason why the temperature inside the plane is always freezing cold

According to Bobby Laurie, a former flight attendant, the ideal temperature of an airplane cabin is between 21 and 24 degrees Celsius. This is the indoor temperature at which most people feel comfortable. However, because aircraft cabins have lower humidity (usually ranging from 10 to 20% at cruise altitude, drier than most deserts) to prevent frame corrosion, passengers may feel significantly colder.

Commercial airlines maintain cabin temperatures within these ranges to prevent passengers from fainting due to lack of oxygen. According to Popular Science, on airplanes, passengers fainting happens quite often, especially during night flights. That's because the air pressure in the cabin is usually kept at an altitude equivalent to 1,800 - 2,400 m above sea level to maintain the integrity of the aircraft.

Although the majority of passengers do not even detect the air pressure adjustment mentioned above, the body is exposed to 25% less oxygen than at sea level. People who are not used to that condition will feel dizzy or lightheaded, or even faint. To limit the risk, flight crews often turn down the temperature, relying on cold air to keep passengers more alert, especially when needing to respond to sudden turbulence or effectively evacuate.

Warm temperatures make it difficult for the body to maintain circulation, the heart beats faster and pumps blood harder, thus requiring more oxygen. Conversely, cold air slows the heart rate, keeps breathing regular and stabilizes blood oxygen levels, preventing nausea and jet lag by calming the body's temperature control system.

Maintaining a cold temperature in the airplane cabin also helps regulate the body's internal humidity. Normally, the low humidity of the cabin will promote moisture on the human body to evaporate faster, causing instant dehydration. But pumping cold air slows down that evaporation process, and makes the surroundings seem less stuffy in the long run.

According to Rosen Aviation, cooler cabin temperatures can reduce the risk of passengers getting sick on a flight. By reducing moisture in the air and eliminating microorganisms through the air conditioning system, cold cabins can limit the spread of bacteria and germs that are more active in warm environments.

Airplane systems also operate more effectively in cold conditions. Cool air helps the aircraft's electronics dissipate heat and maintain optimal engine heat levels, contributing to increased system efficiency and longevity.

All commercial aircraft have an integrated Environmental Control System (ECS) that manages the aircraft's cabin pressure, temperature and air quality. ECS distributes conditioned air to several separate areas throughout the aircraft. The passenger cabin is usually divided into 2-4 independent temperature-controlled zones (e.g. front, middle and rear zones). To manage temperatures in specific areas, aircraft use adjustable air valves, which introduce small amounts of hot or cold air into the main air ducts, allowing local temperature adjustments.

Some aircraft are capable of assessing the cabin environment in real time thanks to thermal imaging technology and monitoring systems. This technology helps identify areas prone to temperature changes, thereby making timely adjustments to maintain a stable cool temperature in the cabin.