Air-to-water heat pump sizing in new construction

If your house is insulated, you won't get large temperature differences.

If a room is not heated at all, the heat simply moves from the other rooms there because it escapes less to the outside.
As a result, the heated room also becomes cooler or the heating has to work harder to compensate.

Therefore, I would cover all rooms with underfloor heating, you can still reduce it via the [HKV], but you always have the option to use the room normally.
With 5.9 KW, a 6 kW should be sufficient.

Yes, the 6KW heating capacity will be sufficient. The building's heating load of 5.9KW is only reached at [Norm-AT], which only occurs a few days a year. In addition, the building is completely warmed through and would first have to cool down. As a comparison: a fan heater usually has 2KW. Theoretically, it would be enough to keep the place warm during half of the heating period. Regarding the basement room: my predecessor is right. The only way to achieve a somewhat reasonable temperature difference would be to insulate the interior walls of the "cold" room against the tempered rooms. Whether this is reasonable and might possibly cause problems related to moisture damage would have to be examined.

Isn't it required by the Energy Saving Ordinance that all rooms within the thermal envelope must be heatable from a certain size? Apart from that, I see it the same way as my predecessors. Heat flows from the warm rooms to the cold rooms, which leads to an increased heating load of the warm rooms, which in turn leads to a higher supply temperature. The heat pump operates less efficiently, heating becomes more expensive at the same room temperature.

Thanks for the feedback! How does it actually look with hot water at the NAT? The heat pump wouldn’t have a buffer anymore and would have to heat with the heating rod, right? The energy consultant calculated a 27° hot water share.

Regarding the basement: the calculation according to KFW55 apparently worked. However, the room heights are also below 2.4m – maybe that’s why heating isn’t necessary?

Honestly, I’m a bit lacking the energy to have the two basement rooms heated afterwards. Because of the discussion with the general contractor. I would now rather focus on the heating installer really doing 17x2 and adhering to the laying distances and heating circuit lengths. Also, it seems he doesn’t enjoy the wall heating topic.

The calculation works out so far that I get more heat in the living-dining area than I need, and despite the cold basement below, the guest WC still manages to get 22°C.

You have a significant overlap in all rooms except the bathrooms and the gallery.

If the area under the bathtub is also planned in the bathroom and the wall heating is added, you can:

- Achieve the desired 24 degrees in the bathroom and throttle down the other rooms or run higher temperatures there as well.

or
- Accept lower temperatures in the bathroom and lower the flow temperature instead.

You must not forget that the design is planned for the worst outdoor temperature case, which means most of the time the heating can operate with a low flow temperature.

In the case of the basement, my setting would be better to have than to need.

Have you planned a controlled residential ventilation system with heat recovery?

If the heat pump activates the electric heater on the few NAT days, that can be neglected.

Hot water plays a rather subordinate role. Unless you continuously use hot water and constantly need to reprocess it. Otherwise, there are simply 2-3 hours a day for hot water preparation. Considering the heat energy stored throughout the entire house, this will not make a significant difference. The heating element is most likely just there for peace of mind.

Regarding the underfloor heating: You now know the consequences. They will not be dramatic. The points you described are really more important. Pay close attention to them, and you will be better off than many others.

By the way, 22 degrees is not little when almost all surfaces are warmed through. Also, it automatically gets warmer as soon as the shower is turned on. So you really don’t need to worry about that.