ᐅ Decentralized ventilation only in individual rooms for new construction to KfW 55 standard?

Hello,
we are currently leaning towards a decentralized ventilation system with heat recovery. However, we only want to install such a unit in the bathrooms and the master bedroom. That means we do not want to install it in the children's rooms, office, and open-plan kitchen/living area. We plan to ventilate these rooms manually. Does this make sense? Is this feasible?
Best regards, Albert

Why wouldn't you want this comfort gain in every room?

It is possible and makes sense if you need to save a few euros and spend a lot of time at home to be able to ventilate regularly.

KFW55 standard without a ventilation system should theoretically be possible. However, since you would be losing quite a bit of energy through ventilation according to the documentation, the floor, walls, roof, etc. will likely need better insulation. Whether this ends up being cheaper overall than using a decentralized ventilation system is questionable.

We are building a KfW55 house (this year) without a mechanical ventilation system with heat recovery. So it is definitely possible.
For us, it was a matter of cost (easily saves around €12,000).

Our wall construction (timber frame prefab) meets the KfW40 insulation standards (already standard with our general contractor).
Therefore, the mechanical ventilation system with heat recovery is not necessary. The KfW application was also approved without any issues.
Only in the bathroom will we install a decentralized unit. Why? Because that’s where the shower is, and the washing machine and dryer are located, and laundry will be hung there. To be safe, we decided to install a unit in that space.

Interestingly, every sales representative (house manufacturer) advised us against using a mechanical ventilation system with heat recovery. Even the civil engineer in the family recommended against it.
Apparently, the majority of houses are now being sold without mechanical ventilation systems with heat recovery again (according to two manufacturers). Whether that’s true, I can’t say. I was surprised by that as well.

FoxMulder24 schrieb:

Interestingly, every seller (the home manufacturers) advised us against a mechanical ventilation system with heat recovery. We also have a civil engineer in the family.
It seems that most houses are now being sold again without mechanical ventilation with heat recovery (according to two manufacturers).

That's quite nonsense. What reasons do they give?