Extractor hood: recirculation or exhaust air for KFW55?

Is your house being built with [Kontrollierte-Wohnraumlüftung]?

We do not have controlled residential ventilation
We have to ventilate through the windows

We do not have controlled residential ventilation
We have to ventilate through the windows

At KFW55? That contradicts itself again: numbers // actions

But it's true, we have a KFW55 house and no controlled residential ventilation, we have to regularly ventilate through the windows

Can it really be possible that I can lose the KFW status with a blower door tested exhaust hood?

The developer said I should just do it myself after acceptance.
What can happen in the worst case?

So we want controlled residential ventilation, exhaust air through the floor slab, no wall box installed, and a chimney with supply air through the floor slab. Our energy expert said that the extraction air is not a problem and is simply included in the calculations for the blower door and KFW55. In the worst case, a window contact switch will be installed to ensure a window is tilted open when the extractor hood is on. We don't all live in Siberia where -40 degree air would flow in. So let's keep things realistic. :)

The developer said I should just do it myself after acceptance. What is the worst that can happen?

Why are you asking here about recirculated air or exhaust air if you definitely want exhaust air? You have a few supporters for recirculated air here, but in the end, you only focus on the possibility of implementing exhaust air with Kfw55.