From around 1000 ppm CO2, it is wise to ventilate more. If the level moves towards 1500 ppm or higher, the air in that room is clearly no longer fresh enough and immediate additional ventilation is recommended.
The practical limit
Up to around 800 ppm, a room is considered well ventilated. Between 800 and 1000 ppm, nothing urgent is wrong yet, but it is a good time to crack a window. From 1000 ppm, many people already notice the difference themselves: a slightly heavier feeling, less concentration, or a vague headache after some time in the room. That is the signal not to wait any longer to ventilate.
Why this limit does not feel the same for everyone
How sensitive you are to a rising CO2 level varies from person to person and from situation to situation. In a small, warm office with several people, the level rises faster than in a spacious living room with two occupants. Factors such as fatigue and the outside temperature also play a role in how quickly you experience a high CO2 level as unpleasant.
How to ventilate quickly and effectively
A few practical ways to quickly lower the CO2 level without cooling down your home completely:
- For a short, intensive airing, open the window completely; five to ten minutes is often enough to refresh the air in a room.
- Open opposite windows or a window and a door together for a faster airflow (cross-ventilation).
- Keep ventilation grilles, if present, slightly open as standard instead of completely closed.
- Ventilate more often and for shorter periods rather than once a day for a very long time, especially in smaller rooms.
Ventilating without unnecessary energy loss
Short and targeted ventilation, as described above, loses much less heat than leaving a window ajar all day. In winter, that is a good rule of thumb: it is better to air out thoroughly a few times a day than to continuously lose a little through a crack.
In short: from 1000 ppm, additional ventilation is recommended, and from 1500 ppm, it really cannot be postponed any longer. More background on a healthy indoor climate and ventilation can be found at dynter.eu.