>This is common wisdom in Germany but the rest of the world ... In Italy, the tradition has always been that when you wake up in the morning you open windows a

>This is common wisdom in Germany but the rest of the world ... In Italy, the tradition has always been that when you wake up in the morning you open windows and let the air change, but the "new generations" are forgetting this, just when houses are built (or refitted) in a much more airtight way. The only way out, mechanical ventilation systems, possibly with a heat exchanger[0]), are still rare, even in new constructions, I have seen a lot of issues in the houses built with (badly designed) energy saving goals (original A and B classes) built or renovated in the last 15 years or so. [0] which bring their own issues, needed maintenance, periodical cleaning of filters, sometimes noise, etc.