Single-family house 140m² KfW efficiency house 55 achievable through insulation and air-to-water heat pump?

First of all, it has to be YOUR house, meaning in terms of floor plan, location, equipment, etc. Once all that is clear, you can have someone tell you (from a reputable energy consultant!) whether you might already have reached such a standard based on your desired equipment criteria. Installing something just to get a subsidy is like wasting money to save a bit on taxes. A general contractor will build you what is probably the easiest way for them to achieve that standard. But you might want less roof insulation or no controlled residential ventilation, etc., but instead this or that. There are a thousand ways to reach this standard, you should choose the ones that suit you. Maybe you can already get your desired house without KfW, in which case I would think about it very carefully instead of being forced to chase after a KfW standard that is ultimately just a calculated value. You can be happy or totally unhappy in a KfW-calculated house...

Even if you have entrusted your construction to a general contractor, get involved in the design of the air-to-water heat pump yourself to end up with an efficient heating system.

Doesn't the energy consultant or the heating engineer calculate how the air-to-water heat pump must be designed to fit my house? What can I contribute as a layperson?

First of all, it has to be YOUR house, regarding layout, location, equipment, etc. Once all that is clear, you can have (from a proper energy consultant!) them tell you whether, based on your desired equipment criteria, you might already have reached such a standard. Installing something just to get a subsidy is like wasting money to save a little on taxes.
A general contractor builds you what he can probably achieve this standard with most easily. But you might want less roof insulation or no controlled residential ventilation, etc., but this or that instead. There are a thousand ways to achieve this standard, you should choose the one that suits you. But maybe you can also get your desired house without KfW, then I would think carefully about it rather than feel forced to chase a KfW standard that ultimately is just a calculated value. You can also be happy or totally unhappy in a KfW-calculated house......

Our general contractor only pointed out after we told them how we imagine the house and what our wishes are that they build the KFW55 as a standard.
I just wanted to ask around here whether this really can be achieved with such "simple" measures. That seems to be the case, so I am satisfied.
We don't need any extra frills that have to be maintained or might have to be replaced over the years if they break.

Even if you have entrusted your construction to a general contractor, get involved in the design of the air-to-water heat pump yourself in order to ultimately achieve an efficient heating system.

Keyword hydraulic balancing and room-specific temperature settings.

Doesn't the energy consultant or the heating engineer calculate how the air-water heat pump must be designed to fit my house? What can I as a layperson contribute to that?

08/15 heating engineer = rough estimate, we've always done it that way. Underfloor heating laying distance 15cm and less in the bathroom = works too, but then maybe needs 38 degrees flow temperature and corresponding electricity costs. Well calculated and planned = room-by-room design with specification of low flow temperature = smaller distances = 28 degrees flow temperature and hardly any electricity costs Both lead to the result of warm rooms. Once not well (ask ) and once well.

Well calculated and planned = room-by-room design with specification of low flow temperature = smaller distances = 28 degrees flow temperature and hardly any electricity costs

Is 28° such a targeted standard value or just an example?
I take from this that the same distance should not simply be laid as standard but that the distance must be determined for each room. However, it should be kept as small as possible to save heating costs (lower flow temperature)?!
Doesn't the energy consultant look at something like this?

Keyword hydraulic balancing and room-accurate temperature settings

Isn't that only relevant when the heating is put into operation? What influences does this have during construction?
Who would I commission with this if I want the heating to be set up optimally, if not the heating engineer?