Decentralized ventilation only in individual rooms in new construction KfW 55?

Hello,
we are currently leaning towards a decentralized ventilation system with heat recovery. However, we only want to install such a device in the bathrooms and the master bedroom. That means in the children's rooms, office, and living kitchen not. We want to ventilate these rooms manually. Does that make sense? Is that possible?
Regards, Albert

Why doesn't one want this comfort gain in all rooms?

Is possible, makes sense if you need to save a few euros and are home a lot to be able to ventilate.

KFW55 without a ventilation system should theoretically be possible. However, since according to the document you then ventilate quite a lot of energy out, the floor, walls, roof, etc. may need to be better insulated. Whether that is ultimately cheaper than with decentralized ventilation is questionable.

We are building a KfW55 house (this year) without Controlled Residential Ventilation. So it is possible. For us, it was a matter of price (easily makes about 12k€).

Our wall construction (timber frame prefab) meets the KfW40 insulation values (already standard with our general contractor). Therefore, controlled residential ventilation is not required. The KfW application also went through without problems. Only in the bathroom will we install a decentralized device. Why? Because there is showering, washing machine/dryer are there, and laundry will hang there. To be sure, we are putting a device in there.

Interestingly, every salesperson (the house manufacturer) advised us against controlled residential ventilation. Also a construction engineer in the family. The majority of houses apparently are now sold again without controlled residential ventilation (statement from 2 manufacturers). Whether that is true, I cannot judge. I was surprised by that as well.

Interestingly, every seller (the house manufacturers) has advised us against a controlled residential ventilation system. Civil engineers in the family as well. Most houses now apparently are sold again without controlled residential ventilation (statement from 2 manufacturers)

Quite nonsense. For what reason?