I left for vacations (New Year) and I had to let my house fully closed during 4 days, so I took a close look on how fast the house alone would be able to recover from the CO2 gas.
As a result it took more than 38 hours to recover from 1276ppm to 450ppm. Normal, but alarming as well. Inside the house there isn’t only CO2 gas but other gasses and VOCs too, as a conclusion gases in general get trapped inside our houses and they don’t “disappear” fast. We have to ventilate our houses frequently.