Interpretation of heat pump - correctly sized or not

Hello everyone,
we are currently building – right now it’s about the heating system. Our energy consultant has calculated the energy demand of our house (should meet Kfw70) – with this we went to the heating installer. Here we received an offer for a heating system that intuitively seems oversized to me.
My question/request at this point is whether someone can assess if the system is plausibly designed or not...
According to the energy certificate, the house will have a final energy demand (per year) of 8.6 kWh/m2 for heating and 6.1 kWh/m2 for hot water. The building volume is just under 1000m3 (the usable floor area of the building is specified as 319m2).
The heating system is supposed to be a brine/water heat pump (i.e. with deep drilling) that heats via underfloor heating.
We were offered a 14kW heat pump...
Can someone estimate from these values whether the 14kW heat pump is correctly sized? Can the heating installer even size it from this info or are important details missing?
Many thanks for your help!!!
Bonagel

...Our energy consultant calculated the energy demand of our house (should meet KfW70) – with this, we went to the heating installer. Here we received an offer for a heating system that, according to my gut feeling, seems oversized.

I am fairly sure that the energy consultant created the energy saving ordinance or KfW certificate. Neither the actual demand nor the consumption can be determined from this. It is even inadmissible! Likewise, it is inadmissible to design or size heating systems based on these results!

...My question/request at this point would be whether someone can assess whether the system is plausibly designed or not...

No one can answer that reliably, for sure.
Various calculations are required in advance here. If the craftsman has not made these, send him packing; otherwise, this could be a money pit.

Best regards.

We have a similar "problem." Our heating engineer offered us an Alpha-Innotec LWC 100 air-water heat pump with 10 kW heating capacity.

The heated area of the house, including partial basement heating, is 200m² with a room volume of 497m³. According to the energy certificate, we have a final energy demand of 22.2 kWh/m²a. Our heating load calculation results in a standard heating load of 6.9 kW. In addition, we will install a wood stove, which should help us with heating, especially in winter (besides looking nice). Here, too, we still need to discuss with our heating engineer why we specifically need this size of the system and not the LWC80 with 8 kW.

Question to the experts here from me: when faced with the choice, is an oversized system more expensive than a possibly too small system where you have to use the electric heating element more often, especially when comparing a few weeks of cold to the entire year? As far as I have read, an oversized system also causes some additional costs?

...Question to the experts here from me. When faced with the choice before buying, is an oversized system more expensive than a possibly too small system where you have to heat more often with an electric heating element, especially when comparing a few weeks of cold to the entire year? As far as I have read, an oversized system also causes some additional costs?

Especially with air heat pumps, the suitable (appropriate) performance curve matters. In particular, On/off devices are no longer state of the art today.

If air heat pump, then preferably fully modulating split units.

Besides the heating capacity curve, the COP curve is also important:

An undersized air heat pump system delivers too little heating capacity, causing the electric heating element to have to "help" too much. An oversized one is equally harmful; on the one hand, the lifespan is limited due to excessive switching, on the other hand, the seasonal performance factor is rather poor.
The planning effort required for ground-source systems in sizing the source is comparable to investing in the performance curve evaluation for air heat pumps. For well-dimensioned systems, the electric heating element share is about a maximum of 2% of the annual heating load.
Those who miss essential fundamentals here are very likely creating a money pit.

Best regards

NB: The performance specifications of air heat pumps are not comparable to those of other heat generators!

I can already tell this is a science in itself and not easy to calculate... Well, anyway, thanks already for the info!

I already realize that this is a science in itself and not easy to calculate...

That's right, which is why precise TGA planning/dimensioning is so important, especially when high overall efficiency (low operating costs) is the focus.

regards