In the end it's all a matter of how much air is exchanged if air from everywhere inside is at least somewhat affected and how high/low the outside CO2 levels ar

In the end it's all a matter of how much air is exchanged if air from everywhere inside is at least somewhat affected and how high/low the outside CO2 levels are. E.g. if you have a apartment in the 5th floor where always have a bit of wind and can open windows so that the wind flows through just opening it for 5min might have as much effect as other people get with 40min. Or e.g. if you have the right kind of wind putting windows into tilting mode can work well and in other cases (like my apartment) you will leak heat with very little air exchange. I have been thinking about using some sort of fan but haven't tried it out. Part of the reason is that in summer I just can keep the window open all the time and currently we have winter temperatures around 4-7C during the day and my room temperature is most times around 16C in winter anyway, so ... it's not too much of a heating problem (compared to people heating their room to 20+C).