Ceiling suddenly too small for controlled residential ventilation!

So, I have now talked to the architect and the installer.

The architect could not help me further, no price concession. In other words, we would have to pay the 4000€ net surcharge for the air-water heat pump as stipulated in the contract.

The installer explained to me why the controlled residential ventilation system does not fit. It is not really due to the space requirement of the device, but he cannot lay the four pipes in the small utility room. (Just "muck it up")
He therefore advises us to go for the air-water heat pump and 2 single-room ventilators with heat recovery; he also thinks the window rebate ventilation is nonsense.

So financially it looks like this now:
+4k€ air-water heat pump
-12k€ controlled residential ventilation
-3k€ gas house connection
+Xk€ single-room ventilation

So you save some money and give up (controlled residential ventilation) comfort.
(The awning for the terrace should therefore be included)

The space under the stairs is not closed off; it should serve as shoe storage / wardrobe.
And yes, the guest/workroom will definitely be used as storage for the time being.

The space under the stairs is not closed off, it should be used as shoe storage / wardrobe.

Also this: an eternal mess under the stairs. With a door, you can at least lock it away.

Please plan the air-water heat pump yourself early, especially have the underfloor heating planned at a maximum temperature of 30°; otherwise, you’d better choose gas, as there is less that can go wrong.

And please define the final ventilation concept even earlier! It is not insignificant for the selection of the air-water heat pump (heating load)! There are good and bad decentralized devices, and the quality of the installation is equally important.

By the way, gas also works with decentralized ventilation units without solar thermal, instead of the air-water heat pump.

Please plan the air-to-water heat pump yourself early, especially have the underfloor heating designed for a maximum temperature of 30°C, otherwise you’re better off with gas, where you can make fewer mistakes.

A supply temperature of 30°C is not always feasible; with small rooms you quickly reach limits. Not every house is built to KfW40+ standards...

Addendum, in case it's unclear: I am talking about the supply temperature at standard outdoor temperature.

When considering decentralized fans, keep in mind that they are not very good acoustically. Probably doesn't matter in a quiet residential area, but in a noisy area they can become a problem.