Newly built single-family house KfW55 standard - How to heat?

With an air-to-water heat pump, you often have double the heating costs in a new building compared to gas. Despite correct pipe spacing and heat load calculation. Only through your own optimization can this be balanced out. It’s harsh, but often the reality.

Actually, the best heating technology is still pellets. Reliable, cheap, and flexible. Underground tank in the garden, done.

With a heat pump, you also have the big electricity price risk. No energy carrier becomes more expensive as quickly as good electricity does.

So far I didn’t want to disagree, but now I feel compelled to.
On the subject of heat pumps: replace your "optimize" with properly adjusting once and it fits. But, as you wrote, it takes time.

Pellets cheap, flexible, reliable? Sorry, but NO! Often need cleaning, errors in suction/transport auger, chimney sweep four times a year, often long transport distances, expensive installation costs.

With an air-to-water heat pump, you often have double the heating costs in a new building compared to gas. Despite correct pipe spacing and heating load calculation.

That is complete nonsense. As if only idiots would install these systems. Choosing a low heating curve takes two minutes, the last 5-10% efficiency won't make a big difference – whether the heating costs are 30 or 32€ per month.

Actually, the best heating technology is still pellets. Reliable, inexpensive and flexible. Underground tank in the garden, done.

Expensive, error-prone and with the largest space requirement.

What about the compressor, bypass valve, thermostats, heating curve, hot water, hydraulic balancing, etc.? All that has to fit, otherwise the heat pump will drain you financially.

Many then can no longer heat the bathroom. All problems exclusively of the heat pump.

Pellets are similarly expensive as a good air-to-water heat pump. Space requirement minimal, have you looked at the new systems? Technically no longer susceptible at all...

The real disadvantage is you need a chimney. But a heat pump without a wood stove would be unthinkable for me in winter, so we also need a chimney there.

have 300, 2 adults, 2 children - that is usually not enough for 24 hours. With gas, it wouldn't matter,

There it is again, the playing. If 300 liters are not enough, the circulation must be reduced. I had problems with that until recently as well. I blocked hot water preparation at night because it is naturally colder and thus more expensive. But the circulation sucked the buffer empty. Over 10 degrees in 10 hours. Currently managed over 15 hours by reducing the circulation.

In fact, you can completely forget about circulation with a heat pump. Another argument for gas.

Really? How is the water temperature set with you? I mean, up to what temperature does the heat pump heat the water and from which temperature does it start?

For us it will probably be a kfw40plus house. And we are not fans of bathtubs. And as far as I have read on the sites, 175l is more than enough.

There it is again, playing around. If 300 liters is not enough, the circulation must be reduced.

We have no circulation. As already written: With gas, for example, 175 is no problem because the tank simply recharges when it is half empty - you don’t notice anything unless you are using the rain shower and filling two bathtubs. With a heat pump it is always recommended to use a larger tank. Our tank is set to 48°, charges around midday when the photovoltaic system cuts the peaks. Of course, there is also individual demand. I usually shower for a few minutes, so not much water is used. My wife sometimes runs the rain shower for 20 minutes; then the 300-liter tank is empty. Or calculated differently: A shower with 20 liters/min flow at 38° will empty a 175-liter tank at 48° in 11 minutes – then you have to wait 20-30 minutes until warm water is available again – or a day, depending on how the heat pump is set.