Construction costs are currently skyrocketing

The fans are not super loud. What I have heard more often is that noise from outside comes in, like through an open window, and always. Well, if you can sleep with an open window at night, you live in a quiet area anyway. You also have to look at the air exchange rates of the devices; on a low setting, much less comes through than with a tilted window.

Noise from outside is not an issue. A tilted window is not comparable to that. 21 cubic meters per hour on the lowest setting (the devices I have). I don't think a tilted window provides much fresh air. There is no draft at all. I am happy with my devices – even though a central ventilation system is even better.

When I search the internet for experiences, the topic of noise from the fan keeps coming up.

Now you have piqued my interest. Will you tell me what you have installed? So far, I have only found ones with fans and corresponding reports about "noise pollution." Thanks.

I have to apologize or rather qualify my statement. I just realized now that it is about the decentralized solution, sorry.

I based my statement on a central system with appropriately installed valves in the rooms. Since I read about heat recovery in your quote and also saw several references here regarding central systems describing "insane noise levels," I had voiced my objection. In this case, with the wrong reference, sorry :)

I have no personal experience with decentralized solutions.

Why do you want to replace a working heater?

Actually not, that was really the first question I asked my mother, why change it if the heater is not broken. :D I probably let myself be infected by the panic that gas heating will no longer work soon. I really need to educate myself more on this.

If I search the internet for experiences, the topic of noise caused by the fan keeps coming up.

Basic ventilation hardly noticeable - that is the mentioned 21cbm/h. Standard ventilation during the day also not - at night it is.

It can also be installed decentrally in noise-insensitive rooms and only [Regelair] in the sleeping rooms. However, larger gaps or ventilation grilles under/in the doors are then required.