Is preparing for an air conditioner worth it?

Zubi123 is right. Evidence: "Information and diligence obligations of the grant recipient Within 10 years after the confirmation of the application, the following documents must be kept by the grant recipient and presented to KFW upon request..." (Quote p. 11 information sheet on application BEG residential building grant 461 Efficiency House) "Furthermore, KfW is entitled to check compliance with the funding conditions on site at the grant recipient (...) The audit rights of KfW apply for 10 years from the date of application confirmation/commitment." (p. 2, General Terms and Conditions for the Application and Awarding of Grant Products of KfW via the KfW Grant Portal)

Zubi123 is right. Evidence: "Information and diligence obligations of the grant recipient Within 10 years after application confirmation, the following documents must be kept by the grant recipient and presented to KfW upon request..." (Quote p. 11 information sheet for BEG residential building grant application 461 Efficiency House) "Furthermore, KfW is entitled to check compliance with the funding conditions on site at the grant recipient (...) The audit rights of KfW apply for 10 years from the date of application confirmation/commitment." (p. 2, General Terms and Conditions for the Application and Award of Grant Products of KfW via the KfW grant portal)

Are there any experiences in the community about this, or are these empty "threats" from KfW?

With all the preparations, I am skeptical. Whenever something has been prepared, fireplace, ventilation, etc., it has later not been carried out.

So you believe that without a recalculation by an energy consultant, we cannot install an air conditioner without losing the KFW status?

We have a semi-detached house from the developer and we are not allowed to install a range hood either because otherwise the KFW status will be lost, according to the developer.

They do not do a recalculation by the energy consultant.

Why should an air conditioning system worsen the energy efficiency of a building? They are promoted by [Bafa] because they IMPROVE the energy efficiency of buildings.

Regarding the initial question: I would install a small (2.5 kW) device at a high, central location in the house directly during construction.

If you let it run as soon as the room temperatures get too high and only turn it off again when the heat phase is over, you just have to leave the doors open and you have comfortable humidity throughout the house and – in the case of a new building – also comfortable temperatures.

Of course, it is better to have a device in every room – but eventually that just gets damn expensive.