Extremely high heating costs with underfloor heating. Incorrect setting?

The orientation, especially during the transitional period, also plays a role, along with three degrees lower desired temperature, different ventilation behavior, etc.

Keep observing this, especially during the heating period. Currently, there is no reason to be alarmed.

Thanks for the information. However, we have noticed that the identical apartment (but East, South) compared to the South/West has a 95% lower floor heating kWh! 30 kWh versus 400! Each with 1 person. Could it be that the East, South apartment is simply heated up so much by the sun that the floor heating (because it is set to 18-20 degrees via the regulator) hardly ever turns on... and the South, West one runs almost all the time due to lack of sun and room temperatures of 21 degrees (one room is not heated at all. So the heat probably moves from the heated rooms into the unheated one). That would explain the large difference.

It's just like with Stasi

It's just like the Stasi

No, just neighborhood help...

Let's leave out the percentage calculation. What sounds dramatic is not. It is the difference between practically not heated at all and moderately heated. That's simply hard to compare.

Obviously, windows closed.

One room is not heated at all. So the heat probably flows from the heated rooms into the unheated ones). Then the big difference would be explained.

Well, it's just normal physics. Many people slept through school and think that if you shut off a room, you would save something. Often the opposite is the case because you effectively increase the areas that need to be heated. Especially with underfloor heating, you should absolutely avoid doing that. Since underfloor heating is practically always on and thus always has to carry along the unheated room.

Or an entire apartment...