Ventilate for air quality, not just temperature

What to check

Do not decide only by the outdoor temperature. First notice how the room feels: stale, humid, heavy, or fresh. If several people have been inside for a while, the windows stayed closed, or the air feels used up, a short air exchange can help.

Open windows on opposite sides if possible for a few minutes. Then close them again and keep the room shaded when it is hot outside. You replace loaded indoor air without warming the apartment more than necessary.

Why it matters

When you breathe, you release carbon dioxide and moisture. Both can build up in closed rooms. So the temperature may still feel acceptable while the air quality is already poor.

The Swiss Federal Office of Public Health describes ventilation as a way to remove unavoidable indoor pollutants; ventilation systems remove CO2 and moisture among other things. That is why ventilation is about more than warm or cold.

Useful timing

Use longer ventilation windows in the morning and evening when outside air is more comfortable. During hot parts of the day, short and deliberate bursts are often enough. This is especially useful after long meetings, focused work in small rooms, visitors, or a shower.

If you have a CO2 monitor or humidity meter, use it as a signal. Without a device, keep it simple: if the air feels heavy or windows fog up, a short air exchange is usually worth it.

Limits

During heat, weakness, breathing problems, or circulation warning signs, personal safety matters more than saving energy or following rigid ventilation rules. Ventilate in a way that keeps you stable, and seek medical help for serious symptoms.