Construction costs are currently skyrocketing

What is also really expensive - we waived it - would have been a basement as a white tank and a massive double garage.

We would have needed a white tank as well.

Since we are building on a 300sqm plot, the basement is actually indispensable with 2 kids in the house. If we subtract the area of the house, the garage, and the driveway (mandatory, parking space regulation), maybe 130sqm of unsealed area remains. After subtracting the terrace, light well, and paths/splash protection strip, even less than 90sqm. The basement is therefore the cheapest area for us. Building a third floor upwards was not possible due to the setback distances.

Maybe the mortgage financiers among the bankers here could help. I suspect that the type of equipment is part of the property valuation.

I wrote it in my post after all.

Edit: by the way, that is not my opinion, but something I read earlier and was confirmed by Finanz-Bank this year.

Sure, there are big regional differences. All the more surprising is the blanket way houses are often dismissed as "social housing standard" because they don't "reach" 3,000 EUR/m².

I haven't read that anywhere here this year or since the crisis at all. Except from you. More like underplaying, while other professional groups besides craftsmen also find themselves in your lower drawers.

It's always a question of what is included in the construction costs per sqm. Only the costs from the [GU], also the incidental construction costs, also the outdoor facilities? The range for us then also varies from 2,200-3,200/sqm.

I have to honestly admit that I haven’t seen a concrete heating load calculation for our house yet, but according to the general contractor, the heating energy demand should be around 20kWh/sqm p.a. Roughly estimated, that’s about 4,700kWh p.a. I already asked him whether the ALM 4-12 isn't a bit "over the top." You can guess the answer. To my shame, I have to admit that I didn’t read deeply enough into the topic in time. Meanwhile, the heat pump is ordered and on its way. There’s not much I can do about it now. :-/ In hindsight, I should have taken the smaller unit, the ALM 2-8.

The heating load isn’t about the annual consumption but the value of heating energy you need at the design temperature. I don’t know that value now, but based on your other data and unless you live at the North Pole, the unit is obviously much too big. Your heating load will surely be below 6 kW, maybe even significantly lower. The problem isn’t so much that it has too much power "on top" (i.e., the 12 kW), but that it cannot modulate down. In other words, you only need 6 kW from my example if it’s -12 degrees for 3 days straight. The other 98% of the year you would get by with 2-3 kW. Yours can’t do that, so it will turn on and off more often. Presumably, this is why the installer gave you a nice big buffer. But if the damage is already done, that’s of course unfortunate.

It's always a question of what is included in the construction costs per sqm. Only the costs from the general contractor, also incidental construction costs, also the landscaping? The range for us also varies from 2,200-3,200/sqm

I always calculate the house including any possible own work (painting...), base slab/cellar, earthworks necessary for the house, but without kitchen, furniture, utility connections, landscaping, notary,...

Since we are building on a 300sqm plot, the cellar is actually indispensable with 2 kids in the house. If we subtract the area of the house, the garage, and the driveway (mandatory, parking space regulations), then maybe 130sqm of unsealed area remains. After deducting the terrace, light well, and paths/splash protection strip, even less than 90sqm.
The cellar is therefore the cheapest area for us. Building a third floor upwards was not possible because of the setback distances.

To be honest, I can't imagine how you build detached on 300sqm. There's really only the setback strip left?

What I also found interesting... both with the tiles and the sanitary equipment, we basically always stayed within the cheapest range that the dealer had in the showroom. Still, I find the almost €9000 for both bathrooms quite expensive and €38/m² for 30x60 tiles not exactly cheap. At least with the tiles, the dealer can quite well keep up with internet prices, so that's probably not the reason

Tiles are fired, gas is involved, it has all become really ridiculously expensive. We recently went to choose tiles as well, and took almost the same combination for the main bathroom that we had in the first bathroom. And tiles that were below the €35 gross standard back then are now at €37 plus VAT. You can still get the house furnished up to the €35 standard, but the selection has really become very limited. We're adding a bit more this time.