Good morning,
I have read through the documents - thank you for providing them and for your trust! - I can't imagine that you signed the contract exactly as it is, because ...
At first, I was offered a KFW 55 house with a white tank and a partially heated basement (2 rooms) while the other 2 basement rooms were to remain without underfloor heating.
... I don't read anything about 2 heated basement rooms - apart from the basement anteroom - in the documents.
Now that it is going into the execution planning, it suddenly says that KFW 55 can only be achieved if the entire basement is heated. For this, an additional 65 sqm are heated and 4500€ more are estimated.
That is - with reservation - almost correct; in general - if no living spaces are planned, insulation of the entire basement is sufficient. This can also be read in your documents: "
The exterior walls will receive perimeter insulation made of XPS rigid foam boards in thickness according to KfW 55 calculation". This is usually sufficient for housing the heating technology in the basement.
In addition, the ground source heat pump must be dimensioned one size larger and the geothermal drilling must be deeper. I don't yet know what the larger heating system and the deeper drilling cost.
In the contract you provided, it states: "
If a larger Vaillant heat pump is required according to the heat load calculation, the corresponding additional price will be charged". If this is also stated in the signed contract, the recalculation is legitimate.
Otherwise, unfortunately, I am just as wise – or equally uninformed – as before, since the documents I received from you apparently differ from the original contract documents. Furthermore, I am _not_ authorized to comment on areas of responsibility reserved for lawyers; in Germany, this is exclusively reserved for the consulting professions!
Therefore, I would like to urge you to seek a conversation with your salesperson or possibly their sales manager and discuss possible solutions. A downgrade to KfW 70 could perhaps be an alternative; on the other hand, the contract also explicitly entitles you to terminate it. Whether this is currently possible, however, should only be answered by a lawyer you trust with a focus on contract and construction law.
As long as your statements here _do not_ match the texts of the documents I have, I cannot and will not be able to give you advice. If I am wrong – even unintentionally – this could cost you a lot of money; I would not want to be responsible for that.
Rhenish regards