20% humidity in KFW 40+ new construction

plus working in the garden, plus sitting on the terrace with the doors wide open for hours ;)

And that in summer as well as in the dead of winter!

This is already drifting off topic again and going in circles.

Can't we at least agree (for half a year ;)) on Controlled Residential Ventilation (with EWT)?

Absolutely necessary: No
Comfortable: You bet!
Cost: Treat yourself (or not)

Absolutely necessary: No

I can only give a yes-and-no answer to that. If you want sufficient air exchange in dense housing, you have to manually ventilate thoroughly 6+ times a day. Nobody does that except absolute ventilation fanatics, and that’s why in reality it’s no longer a matter of preference.

I can only give a yes-and-no answer. If you want sufficient air exchange in airtight houses, you have to ventilate thoroughly by hand 6+ times a day. Nobody does that except the absolute ventilation fanatics, and that's why in reality it's no longer a matter of preference

And that is simply wrong. In practice, 2 to 3 times is sufficient. Otherwise, everyone with airtight houses without controlled residential ventilation would have a problem. And that is not the case.

So, with our house we only chose the standard options or no extras. But I definitely wanted to have the centralized controlled residential ventilation because I neither have the time nor the desire to air out every room several times a day. And in reality, few people probably do that either. Having fresh air all the time is of course also a great advantage; often, after a while, the apartment smells musty when many people stay inside. Since we had to install a decentralized controlled residential ventilation anyway ([KfW55]), we simply added €5,000 and ordered a centralized one. It probably doesn't pay off financially, but the topic of ventilation in such a tight building envelope should perhaps not be underestimated.

And that is simply wrong. In practice, 2 to 3 times is sufficient. Otherwise, everyone with airtight houses without controlled residential ventilation would have a problem. And that is not the case.

You still owe an answer on what your ventilation concept says about the nominal ventilation and why you believe you know better than the experts and that twice is sufficient instead ;) Sorry, but in this respect, you are like my girlfriend. Not concerned with the basics, no desire to deal with it, but completely convinced of your own opinion