It doesn't work in a flat (well unless you are under the roof), but in my house I have 2 electric opening in the roof (velux) that I open nearly (unless rain) d

It doesn't work in a flat (well unless you are under the roof), but in my house I have 2 electric opening in the roof (velux) that I open nearly (unless rain) daily for 5 minutes to change the air and it works really well, whole house drops to around 450. I compared with opening only a "regular" window, and it doesn't work very well, the air stagnate around the window and the CO2 only drops within a few meters of the window, but still cools the house. I guess it's basic physics as hot air is lighter, but it shows the importance of air flow. Also, changing the air quickly conserves more energy as the rest (furniture, floor...) doesn't have time to cool.