Interpretation of heat pump - correctly sized or not

@€uro: Thanks also from my side for the detailed explanation!

Also something from me on this topic. Please give me your assessment:

Our air-to-water heat pump has a performance range of 3.5 to 7.0 KW.
We built a solid energy-saving ordinance standard house without controlled residential ventilation with (including basement) 226 heated square meters. No KfW. Underfloor heating. Household of 4 people.

The heating system seems undersized to me. Am I right? Neighbors have smaller houses and larger devices from the same manufacturer.

The heating installer himself calculated a standard building heating load of 7828 W. So more than the air-to-water heat pump can provide. Domestic hot water heating is not even included as far as I understand the calculation.

Did I misunderstand something or did the heating installer really dimension it too small?
Can I insist on a retrofit?

I fear high electricity costs due to frequent use of the heating element.

Thanks in advance

Depends on how he calculated it, also depends on how your house is positioned and oriented, how often you are at home, where your house is actually located, etc... Generally, you can say that it does work if the calculation is correct. If an air-to-water heat pump is oversized, it cycles a lot and in the end you consume more electricity. Not having a controlled residential ventilation is just a stupid mistake, so you shouldn't overdo the ventilation at -16°C. I have a heating load of 5400 W, the pump is 5 KW and did not need this capacity even at -14°C over several days.

How many square meters do you have?

We installed 4 decentralized little fans for peace of mind. However, I think we will not miss the controlled residential ventilation. We wanted to build conservatively. Poroton bricks. Red lime plaster everywhere. No external thermal insulation composite system. My wife ventilates diligently. The room climate should be fine.