February 29, 2024

Science Question – Does fresh air warm faster than old air?

Shock ventilation when the air in the room is already “stale” not only brings fresh air, but is also energy saving.


sIf you sit all day at the office or in your home office in your own kitchen, you sometimes notice that the air in the room is no longer fresh. It is seen as “old” and is often replaced by fresh air ventilation. Thomas Westahl, meteorologist at GeoSphere Austria, explains why shock ventilation is also an energy efficiency measure.

When we talk about “stale air” meaning air with high humidity in living rooms, for example due to washing, cooking and the presence of people, the saying that “stale air” heats up faster is correct. Water vapor requires more energy to heat than other components of air. Therefore, old, moist air heats up more slowly than dry air. Physically: Water has a higher heat capacity.

Thomas Westall, The Atmosphere of Austria

Thomas Westahl is a meteorologist at GeoSphere Austria. This has been the Austrian Federal Institute of Geology, Geophysics, Climatology and Meteorology since 1 January 2023.

Geography of Austria

Therefore, if it is colder outside than in the room, and there is ventilation, the “stale air” that is unpleasant for people will be removed at the same time. Fresh air entering the room through the open window heats up relatively quickly to the previous room temperature. Therefore, “shock ventilation” is a very effective measure to improve indoor air with as little heat loss as possible.

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