Is a central ventilation system absolutely necessary?

After having a decentralized one in the apartment and now a centralized one in our own house, I can confirm Bookstars' arguments. Our decentralized one was too annoying to sleep with even at the lowest setting, especially because of the constant switching of air direction every few minutes, and it felt like an open window for the sound.

We will also include a central controlled residential ventilation system, and I am generally positive about it. The fresh air side of the system does not worry me; rather, it is the exhaust side, especially the heat exchanger. Due to an open room design with a gallery – the air space between the ground floor and upper floor – it is hardly possible to prevent moist, greasy, and odor-laden kitchen air from being extracted in many places throughout the house. The moisture then partially condenses in the heat exchanger, so that fat and other particles inevitably separate and deposit there. As long as the system is active, odors are directed outside, so no problem. However, as soon as the control temporarily pauses the system or runs it at the lowest level (e.g., due to temperature), opening the front door during windy conditions, etc., can create a negative pressure in the house, which can be balanced by a short counterflow from the exhaust side of the controlled residential ventilation system. Then odor-laden air enters the living spaces. That means regular, professional cleaning of the system seems indispensable, but it will not be cheap because it is time-intensive. Odors are also a tricky matter; people who have lived in their house for a long time do not perceive increasing odor loads over time, which then supports the experience reports "it doesn’t smell even after 10 years." Overall, I do have my concerns as the house becomes more concrete. However, giving it up is also not an option for well-known reasons. ...dilemma...

The ingress of odorous air into the living spaces that you described has not occurred for us, not even at a low setting. The kitchen air should actually be quite freed from grease, etc., by the extractor hood. Then there are also the filters in the exhaust openings. And whether a house smells or not, you notice that yourself, as you always come in fresh from outside. Either it smells then or it doesn't. I think you have a rather theoretical fear that practically plays no role.

Because of odors and grease, we do not have a gallery, but a rather open design. The exhaust in the kitchen is located between the oven and the stove. Together with the extractor hood, there is no smell of food on the upper floor and in the open living area, only as long as, for example, something is being fried. I have not been able to detect any odor exchange in the rooms due to negative pressure. A frying smell is noticeable.

Directly in front of the exhaust outlets we have a filter that is regularly cleaned or replaced. Currently, cleaning is necessary once a week - in winter it was less. I have not detected grease on the exhaust filter and exhaust duct in the kitchen. Directly in front of the heat exchanger there is another exhaust filter installed. When the heat exchanger was removed in May, I could not detect any contamination. I am curious to see how the summer cassette will look in autumn. It is easier to inspect.

We have a Stiebel LWZ 604 Air or Tecalor TCO 2.5 (identical).

Sounds reassuring! Thank you. Yes, my fears are theoretical in nature, as I said, not installing a system is not an option anyway.

Can anyone say what the temperature of the exhaust air at the exhaust outlet usually is? My idea was to place the side exhaust duct in the technical room so that it opens into the adjacent double garage in order to use the residual heat there and, for example, to stay frost-free in winter. Of course, the garage must not be 100% airtight; what flows in must also be able to flow out again. In my opinion, that would be a perfect use of residual heat, but the resistance when blowing out into the garage must not be too high so that the controlled residential ventilation can also "breathe freely."

Ps. I can already see the faces when I come up with the suggestion: we have never built it like that before, it doesn’t work because... and because... and anyway, we couldn’t provide any warranty then. Yeah yeah, then the residual heat just dissipates unused into the open.

In front of the exhaust vents, there is a filter that is regularly cleaned or replaced. At our place, cleaning is currently required once a week.

What now? Clean the filters at the exhaust openings once a week? At all of them? Seriously?
Then I would just be running around all the time? Why is that?