More polite to leave bathroom fan on or off?

[Thudlow_Boink]

Houses are not and should not be literally hermetically sealed. In another recent thread, I learned about how many air changes per hour they’re supposed to have.

Why does my apartment require so much water from my humidifier to increase the humidity

That’s incredibly aspirational though. The Passive House standard, the toughest building standard in the world can be passed with 0.6 ACH. Modern building codes tend to mandate somewhere around 3ACH and older houses would often have 15 - 25 ACH.