Optimization of floor plan for detached single-family house 155 sqm

You cannot equip only the upper floor, at least not meaningfully. Pipes of the flat ducts can run in the floor or ceiling, but this must be prepared.

The bombshell came now with the ventilation system. Instead of the TTL 4.5 ICS TSBC eco, we are being offered a combined unit. The heating and ventilation device THZ 5.5 eco comes with a surcharge of a hefty €21,000.
I cannot understand this additional cost. But since we are bound to the supplier, we cannot obtain any further offers.
Therefore, we will most likely forego the ventilation.

I don’t even understand a word. One device is supposed to be replaced by another model – at whose instigation and for what reason?; at a surcharge that sounds more like a total price based on the order of magnitude. What binds you to the supplier, on the one hand (a proprietary bus system or something like that?), and why is it on the other hand dispensable without replacement?
If an agreed part of a delivery item is “out of stock,” it must be replaced equivalently; the risk of additional costs does not fall on the client side (unless you were responsible for a late order). I can hardly imagine such a contract: “The main object of the contract is delivered as a pig in a poke, alternatively a goat at the price of a rhino or nothing, but a universal pre-installation is excluded”?
I also see the contractor as accountable for how they calculate the surcharge, if and why they expect you to share in it. Just send us all your money, it’s urgent, unfortunately!?

And time is running out a bit as well. The house is to be erected on March 3rd.

Then we are now already at D-Day minus 37. It seems to me you heard the announcements for the final boarding call too late. That you can’t conceive a child in the ninth month should have become common knowledge. Or are today’s homebuyers no longer informed about that?

Of course, we can keep the heat pump without the ventilation system. We only requested a ventilation system and received the corresponding offer due to the feedback from the forum. And regarding the appointment for installation: the approval of the funding came as a complete surprise (the application was in March 2024). Both the builder and we had expected a later date. Therefore, we were not in a hurry to make a decision until now.

And time is also running out a bit. The house is supposed to be set up on March 3rd.

This progress was unknown to me, otherwise the floor plan discussion probably wouldn’t have taken place like this; so it is a prefab house?! .....and again, the system must also serve the ground floor. If it is prepared and also Olatz is in the utility room, you can do it even after acceptance. I don’t know your conditions, with us the construction sometimes stood still for 6 weeks and before moving in we first had to drive away several bird families who lived there. The wagtails come back every summer and go back in - home, basically. I think you have now gotten a few ideas here on how you can try it.

What exactly is the difference amount from WP to WP incl. [Kontrollierte-Wohnraumlüftung]? And what would be the price for a completely separate [Kontrollierte-Wohnraumlüftung]? Would the pre-installation be accepted? That's not so much, a. You should also address questions, otherwise it will get even more complicated. Are you forgetting the [EG]?

We had also been offered the THZ 5.5 eco from a prefabricated house provider. The price for the complete unit was according to the offer: 40447 euros.