KFN house without ventilation system - Experiences

Explain to the OP how your airing concept looks like.

Open the window now and then.

The heating plays no role in this. The stale air doesn't care whether it is warmed with gas, heat pump, underfloor heating or radiators.

The "stale air," as you call it, doesn't care. But the heating system does influence how much energy you lose when airing. Convection systems are much more susceptible than radiant heat systems.

The room size is also irrelevant.

You underestimate what air volume means. The smaller the air volume, the faster the stale air per person becomes noticeable.

A bedroom in a modern house is, for example, always a "problem" at night.

That is something special with us: We don't have a bedroom, but a "living space," which truly deserves its name.

Incidentally, the choice of materials around the room is also a component with which one can emphasize the "stale air" more or less. (And I am NOT talking about the much-discussed "breathing" walls.)

Since you certainly neither measure CO2 nor VOC, you have probably simply gotten used to the stale air or you ventilate manually 6 times a day.

Since you probably neither measure CO2 nor VOC, you have probably just gotten used to the musty smell or ventilate manually 6 times a day.

Where you are right: We do not measure. Where you refer to a known effect: People are less sensitive to their own odor than to foreign odors. Where you are wrong: The assumed necessary ventilation frequency. I assume that you are starting from false premises. Try to fully create a musty smell within a day with 2 people in a room volume well over 300m3 with wood or clay plaster surfaces that act as moisture regulators (where there are no windows).

We have a partly similar living situation as and before that we lived in two different houses (each with a similarly open design) without controlled residential ventilation. Even though I now have controlled residential ventilation in the current house, it is simply not as extreme as portrayed here. As always, context is crucial, and two people (sometimes only one during the day) in such a large room do not cause anything I would even remotely call stale air. Because of this concern, we run such a measuring device, and in fact, we could also live here without controlled residential ventilation without ending up in a mold drama or dying from bad air.
I would rather have a problem with what I consider nowadays overheated rooms, which I occasionally read about here, or the same temperature everywhere in all rooms, which feels rather synthetic to me, for example.
As I said, I have controlled residential ventilation and would do it that way again, but I have tested it repeatedly and could live under our circumstances without it as well; under our individual circumstances!
In a "normal" single-family house with many small rooms and just as many people, I would see it differently, as airing would also be a big effort there. Here, for example, I have additionally equipped the windows so that I can open them at the push of a button and thus ventilate.
I know people who, despite having controlled residential ventilation, open their windows just as often as they did before without it because their feeling demands it and they subconsciously cannot fully trust the effect of controlled residential ventilation; if you have been used to that your whole life, I can even understand that. That was also my concern, but meanwhile, I can sit inside with the windows closed and feel the sensation of fresh air.

We find the controlled residential ventilation very pleasant. Of course, we also air out sometimes (e.g., after frying steaks). Otherwise, it really does its job well. Bathrooms dry quickly after showering. The fresh air is wonderfully preheated in winter. And since we installed split air conditioners (in summer we have enough electricity), we no longer use the bypass because the heat exchanger also keeps the heat outside. I don't want to do without it anymore - and the extra cost for us was 8000 euros. I'd rather equip the bathrooms myself than save on that.

We find the controlled residential ventilation very pleasant. Of course, we also ventilate sometimes (e.g., after frying steaks). Otherwise, it really does the job well. Bathrooms dry quickly after showering. The fresh air is wonderfully preheated in winter. And since we installed split air conditioners (in summer we have enough electricity), we no longer use the bypass because the heat exchanger also keeps the heat outside. I don’t want to go without it anymore – and the extra cost for us was 8000 euros. I’d rather have equipped the bathrooms myself than save on that.

We have it the same way, and for us, it also comes down to the fact that I go out on the terrace to my grill for the rare times I fry, even in winter. As I said, I would do it the same way again; I can hardly gain anything from a general yes/no. Ultimately, what matters is whether you feel comfortable.