Suitable heating system for new construction - how to choose?

You're probably right. But that's how it is with us. In this case, not ecological. But it was a conscious choice. We don't want to heat with the fireplace and for the few days (I estimate 20) a year that we operate it, it doesn't make sense for us to also use it for heating. Of course, you are also right about the ecological footprint. For that one thing, as I said, we made a conscious decision, just like for a rainwater cistern and a photovoltaic system. It's a give and take. A job e-bike is also coming soon and the car trips by car will cease.

Isn't it the other way around? If you use the fireplace so rarely anyway, it doesn't hurt to also use the heat :-)

Which energy standard are you building to? With KfW40 the room quickly becomes a sauna with a maximum stay time of 15 minutes. But what won't people do to regularly and lifelong have a chat with the chimney sweep.

We are building KFW 55. The fireplace is not used for heating anyway.

We have forest, I know how fast it grows. I also know how much work it is to turn a 15 m beech tree into firewood. And all that just for the aesthetics? I don’t bake a cake just to look at it and then throw it away.

Of course, I thought about what you wrote and contacted our stove builder about it. Apparently, I misunderstood him. Here is his answer:

"The heat that the insert radiates into the heating chamber should not be discharged through the chimney. I apparently did not explain that to you properly. Storage stones are to be installed around the insert, which then store this radiant heat and keep the system warm even when there is no fire burning in the fireplace. This way we achieve a high efficiency and you make very good use of the fuel wood. I would not recommend a stove insert with a water heat exchanger, and not only because of the very high costs."

Yes, that's the theory. The fireclay bricks do buffer the heat somewhat, but eventually it still gets warm.

At least it is not given away. The stones buffer and store. You get a proper burn then, and the stones definitely store until the next morning. From that point of view, everything was done right after all.

Well, the place is warm even without a fireplace. The additional heat is actually too much. Or do you want to freeze beforehand? After all, the temperature increase is buffered.
But you have to turn off the underfloor heating because of that, and the screed starts to cool down (warm air rises up), so the actual heat storage mass of the house then requires the heat pump to do extra work through a temporarily increased flow temperature.
A maximally efficient underfloor heating is not regulated and runs continuously. Day and night. The fireplace slightly reduces the total heating demand from the heat pump, but makes it less efficient over the year. And it still gets too warm with fireplace use. Therefore, sometimes airing out and increasing the heat pump heating demand again.
Nowadays there are even artificial fireplaces that look no different from real fireplaces. And they cost no more than 10-15k€.
If the wood is not sufficiently dried, wood actually releases more CO2 than coal.
There is also fine dust delivered free of charge.
We simply have to stop constantly burning things, and a fireplace cannot be rationally sugar-coated.