Is controlled residential ventilation necessary with expanded clay and KFW55?

It's enough if he does some research. He can find a lot about it here. There is a reason why most people turn those things off. They are too expensive for that.

Many forum members here find those things great, as long as a central system cannot be installed. I have them too and think they are good. I don't know anyone who turns them off. Why would they?
Always fresh air, affordable, quiet, and eligible for funding.

After consulting with our building consultant, the cause of the necessary screed and floor elevation has apparently been found: the ceiling between the ground floor and the upper floor is only 12cm thick, and thus there is indeed too little space due to the underfloor heating.

I have now initially asked the developer about the additional costs for 5cm more intermediate ceiling.

Another option would be to completely remove the trade Controlled Residential Ventilation from the construction and outsource it externally.

Many forum users find these things great, as long as no central system can be installed. I have them too and think they are good. I don't know anyone who turns them off. Why should they? Always fresh air, cheap, quiet, and eligible for funding.

Experiences vary that much. The vast majority turn them off because of the noise; they are simply extremely disturbing. The draft when sitting nearby is also very unpleasant. Personally, I also found the heat exchanger rather poor. But I can only speak for Lunos and Meltem. Maybe there are better manufacturers, but I also don't think much of the technology; drilling a big hole in every wall makes no sense to me. Cleaning annoyed me as well. These things get very dirty and are complicated to clean. And you don't do that just once but with every device.

After consulting with the developer, it is not possible to lay the ducts in the filigree ceiling. However, they can be installed in the insulation of the screed. For this, the screed would need to be raised by about 5cm. Additional costs of €3,000.

The ceiling height on the upper floor would then be 2.45m, which is sufficient in our federal state. Thus, we would save the €5,000 for a ceiling increase.

Now I have informed the developer that I would prefer a Zehnder Q350 instead of the Pluggit AP310. I am curious about the next discussion..,

Now I have informed the developer that I would prefer a Zehnder Q350 instead of the Pluggit AP310.

As is well known, I am someone who prefers to ventilate analogously – one can probably assume that I am not exactly keen on chasing detailed information about controlled residential ventilation either. Nevertheless, I dare to suggest that my Steine mantra might also apply here, and I would not impose "too many" standard deviations on the developer. So at least not another brand, and beyond that, I tend to prefer decentralized here, especially if he has so far avoided any experience with controlled residential ventilation anyway.

I also see that very critically. I am 100% on the side of the elephant.