Air-to-water heat pump sizing in new construction

Yes, the specialist planner has gotten back to us in the meantime. The larger pipe is better for more efficiency. However, nothing changes in the design. In order to reduce the total volume flow, he had to increase the spread to 5K. The forward flow is then at 33.5. Not great, but we haven’t had -12.4°C in Berlin for ages either...

For me, it will now definitely be the 75 model heat pump. The heating technician had the heating load calculation put together and offered again from Vaillant. "Unfortunately," he also said that Vaillant had approved the 55 model heat pump for my construction. However, it unfortunately does not meet the BAFA annual performance factor. He will also not certify any values for BAFA, for which the underfloor heating is not designed – keyword "repayment" under point 55 of the information sheet.

The surcharge for the Vaillant package compared to the standard Daikin Altherma 3 R heat pump and ZEWO Vent ventilation with rotary heat exchanger is supposed to be just over €7k and will not be significantly lower with the smaller heat pump. Unfortunately, the BAFA subsidy then overcompensates the heat pump optimum.

With this, I can hopefully live somewhat efficiently for >15 years. The plan is then to carry out the ideal replacement procurement after optimal thermal balancing.

Thanks to everyone who helped me! I will definitely provide feedback on how it looks in practice. :)

... As long as it stays with the aroTherm plus, it can only be the 75 because of the eligibility for funding. My heating engineer also doesn't like to install the split units that much, since he wants to switch to R290 in the future.

Without having to/wanting to read everything here now, the following question: We are planning to modernize the heating soon (currently oil). The Arotherm caught my attention, also because of the seasonal performance factor of 4.5. We have underfloor heating and two radiators. Are there already experiences with this model? Is the model also suitable for areas with longer frost periods?

... Edit: I just noticed that he did not install underfloor heating in the tiled shower in the guest bathroom. I need to mention that again. ...

We were advised not to install underfloor heating in the shower because otherwise the pipes can dry out and develop unpleasant odors.

Strange argument, if the pipes of the underfloor heating were to dry out, it would happen even without direct installation. The screed under the shower also gets warm without laying pipes there.

Nonsense, if you shower more or less regularly, nothing dries out there. But it makes a big difference whether you step on the cold or warm tiles when you enter the shower.

So I would definitely have the pipes installed in the shower.

The emphasis in this case from the heating engineer is strongly on "can" but it doesn't have to be.