Energy consultant for a KfW 70 house costs 2,500€?

I am not against a controlled residential ventilation system. I have one myself. But purely for comfort.

Which regulation forces you for comfort?

The architect is certainly not to be held responsible for the client's usage behavior. Therefore, there is nothing to gain there, because regular shock ventilation is quite (legally) reasonable.

Otherwise, I agree with you, the controlled residential ventilation system is a comfortable way to save manual ventilation and always have fresh air. For allergy sufferers, it is also filtered. For energy reasons, I would never have a controlled residential ventilation system installed, but certainly for comfort or mold prevention.

One is forced to follow a ventilation concept according to DIN 1946 - usually the architect. Whether it makes sense or not is another question. But planners often prefer to simply plan a central ventilation system - done. (Of course, there are alternatives).

Did you take out Kfw 70 funds? If yes, you will need the confirmations at the end of the construction and when applying for the funds. Also this blower door test or whatever it's called. He should participate after all.

8 square meters?

1 linear meter of thicker wall (5cm) is 0.05 sqm. 20m then make 1 sqm.

8 sqm are therefore 160 linear meters (per floor).

If the house is not exactly a villa with 2,500 sqm of living space (no typo), I do not want to follow the architect's statement.

Of course, I agree that construction supervision beyond KFW55 is not needed, but pacta sunt servanda. Even if it makes little sense (quality control is possibly given anyway).

But you do collect the subsidy for the consultant (1,250) plus the KFW subsidy (5,000 Euro?). That should make the stone affordable.

Or am I forgetting something in this milkmaid calculation?

You forget the terrible loan conditions of the KFW, which relativize the €5000 repayment grant.

I am not against a controlled residential ventilation system. I have one myself. But purely for comfort.

I didn’t understand it that way either. I have one for the same reasons.

You are forced to have a ventilation concept according to DIN 1946 - usually the architect.

That’s true, you are forced to have a ventilation concept. But it can also state that the infiltration air volume is above what is necessary for moisture protection, and then that is fine.

However, no one basically forces you to have a controlled residential ventilation system, only to ensure that (mainly) moisture protection is guaranteed.

If a planner fails to point out that there is no ventilation concept, they are liable for mold damage, that is true.

But (as you already said) there are alternative options to controlled residential ventilation (e.g. the mentioned window rebate ventilation), but only if the ventilation concept deems ventilation necessary.

By the way, moisture protection must be independent of the user and must not be based on residents regularly ventilating. I was indeed wrong with my assessment there. Sorry.

If you then look at the BAFA subsidy, you quickly realize that a significantly more efficient brine heat pump is not significantly more expensive than an air heat pump.

We just had this somewhere else recently. I consider the statement wrong and dangerous as a blanket statement. It crucially depends on how the heat source can be accessed. Not only the costs (drilling etc.), but also the geology. Is the ground suitable for regeneration, how deep can you go down, what is the extraction capacity, etc.

Under suitable conditions, it may be possible to get the brine-water heat pump for a small additional cost, making it economically viable.
However, it is not suitable for generalization, because even my case disproves this universality

If you want to contribute your own work, you can easily create a source with an earth collector, flat collectors, or trench collector for 1000-2000€ - without having to take a drilling.

You just have to like it. If you then have a malfunction and are sitting in a cold house, I want to see the emergency service that takes care of you. If you build the trench collector together with a heating technician, then that might be okay. Especially with central house technology, I would always keep an eye on service, customer service, etc.
And anyone who thinks that a heating system (whether heat pump or gas) is super robust and never breaks down might want to consider why there are 24-hour emergency services.
But certainly a matter of personal attitude. For me, it wouldn't be an option; I'd rather pay a little more once and then not be left out in the cold if something happens.