Extractor hood - Are the headless hoods recommended?

What happens to the controlled residential ventilation when the entire volume flow reverses completely for one hour? Maybe something freezes, overheats, or gets wet, or the filters are backflushed and the dirt lies in the ducts. I am not familiar with that. In ventilation systems of building technology with heating, cooling, drying, and humidifying sections, that would be the case.

Whether with or without [Kontrollierte-Wohnraumlüftung], of course you open the window when using the extractor hood!?

The [Kontrollierte-Wohnraumlüftung] continues to blow its 200m3 in and out, and the extractor hood draws 800m3 from the window to the outside. Nothing should reverse there. Of course, it can now happen that 30m3 from the window goes directly back to the [Kontrollierte-Wohnraumlüftung] kitchen exhaust and 30m3 of supply air from the living room flows directly to the extractor hood exhaust.

With that, you can save around €400 per year.

Complete nonsense!! Such a loss is not present there. If we had -25°C daily for 3 months, there would certainly be a loss, but with normal German weather it is so minimal that you hardly notice it. According to your calculation, in the following scenario: 1 house with 2 kitchens (basement and upper floor) there should be an €800 loss. So put in 2 wall boxes, then only shower lukewarm and my gas supplier should pay me money every month. HA HA......:D

cool, I absolutely have to have this [Mauerkasten]. Then my heating costs = 0.