How do room thermostats work with an FHB?

If the heating water is higher, the underfloor heating simply runs shorter; if the heating water is lower, the underfloor heating simply runs longer until the desired temperature is reached. But running longer does not mean increased heating costs?

Property. It is always more effective not to send the heating water into the house at a high flow temperature, but rather evenly at a lower temperature. It is also gentler on the heating system. Kind of like a car. Constantly turning it on and off for short trips is not good; driving several thousand kilometers evenly at 100 km/h on the highway is gentler. You can also notice this in fuel consumption = heating costs.

Plot. It is always more effective not to send the heating water into the house at a high flow temperature, but rather evenly at a lower temperature. It is also gentler on the heating system. Kind of like with a car. Constantly turning it on and off for short trips is not good, driving many thousands of kilometers evenly at 100 km/h on the highway is gentler. You can also notice this in fuel consumption = heating costs.

Alright. So better to drive longer in 5th gear than shorter and faster in 4th gear. That makes sense. Thanks

If by "die Fußbodenheizung schaltet ab" you mean the heat generator (heat pump, gas boiler) is turned off, that is usually not the case.

The heat generator runs as long as there is still a heat demand.
In other words, if even a single room’s controller is still open, heating will continue.

Just follow parallel threads - that is also being discussed!