New single-family house, gas or heat pump, target KfW55

Hmm, if you have a gas connection nearby and don’t need a tank, it’s always something to consider. Sure, the running costs are still cheaper with the air heat pump, but a gas condensing boiler is significantly cheaper to purchase, and you can pay the higher running costs for a long time. Especially with small capacities, in my opinion, you should never decide without looking at another option, because the basic setup of a heat pump is more or less always the same. A slightly larger compressor, evaporator, heat exchanger, etc. doesn’t cost that much more. I don’t have a gas connection within 10 km, so I’d have to pay for a tank, delivery costs, etc., which makes no sense. I agree with you about the 55/35°, BUT: you have a buffer tank in the circuit. So it doesn’t fully go into the heating system and there shouldn’t really be any overshooting. Can you not find anywhere or do you have no experience about how cold it really gets in winter at your location? The standard outdoor temperature is one thing, but -20°C is not uncommon for me, and that’s where the heat pump is really challenged. Just wait and see what heating output actually comes out. Then you can still keep looking. You have a WRL, if I remember correctly. In 97% of cases, a preheater is installed to prevent icing of the heat exchanger in winter. That naturally adds to the capacity you need for the total heating output.

I myself come from the Bremen area, so northern Germany. Temperatures around -15°C are rather rare here, but that is my own assessment. The gas connection is on the property. The ventilation is to be provided by the air-water heat pump (323DK) and this is also the big sticking point when it comes to the price. With the heat pump option, this is basically included, with the gas condensing boiler option I have to buy it additionally for €8000 (or €10,000 with cooling function), but then a ventilation system with heat recovery. Construction is clearly planned.

....I have previously carried out the heating load calculation with an online calculator...

My heartfelt condolences ;-)

At the back of the PM are my climate data. Although I am much further south than you, it is unfortunately extremely cold in winter here (well, on the other hand, I only drive 15 minutes to the next ski resort) and nicely warm in summer (39°C regularly measured this year :) If we haven’t had at least a week with -15°C or less in winter, it hasn’t even been a proper winter here. An additional 8k€ for a decent WRL is certainly something. Luckily, I don’t have to pay that, it’s "a bit" less since I work for a manufacturer.

Heartfelt condolences ;-)

Well, it is at least an indication in the right direction.
That this calculation does not replace qualitative advice is clear to me already. :rolleyes:

Can someone tell me how I can edit a post afterward?