Decision for a heat pump

Received several offers as mentioned, and they were within this range. However, 17 kW was predominantly mentioned.

Therefore, one has a heating load calculation done by the engineering office beforehand before having a botched installation done and incurring exorbitant electricity costs as well as short lifespan.

I've checked again: the heating load is 17 kW. What does high electricity costs AND short lifespan mean?

Who calculated the heating load with which values?

That definitely means high electricity costs....

I cannot provide values for the insulation, except that the walls are very thick, very thick styrofoam is applied on the outside, the intermediate ceiling is thicker than usual, and the windows have triple glazing. So far, the heat load calculations for the heat pump have always resulted in a value between 12 and 17 kW.

So the walls, the top floor ceiling, and the windows have good insulation? Did I understand that correctly? Then I consider the advised heat load of 17 kW at NAT to be clearly too high and doubt it. What does it mean that your gas heating system will give up soon? Is there a hydraulic balancing? Is there a basement and is the ceiling insulated? Why is there only frost protection in the outbuilding? Do you only need that temporarily? How many rooms does the building have?