Construction costs are currently skyrocketing

Theoretically heat recovery. But a fan in the bedroom would drive me crazy.

Unfortunately, that is a completely wrong assumption! Properly adjusted valves deliver fresh air absolutely silently. Ours, right next to the bed, is inaudible in terms of noise.

Ok. Then the device needs power, right? So just a hole in the wall isn’t enough? And it’s also not a solution if you want it warm during the day and cool at night.

That’s the great thing about heat exchangers: they work both ways... in summer they cool the warm air and in winter they warm it up. Of course only to a certain extent, but better than opening the window and losing heat.

What would actually be the heating for the average consumer if the gas heating is currently installed but should slowly be replaced after 30 years? At my parents' place, a house from the early 90s. To be honest, I'm clueless.

Why do you want to replace a functioning heating system?

It must already be replaced if it is really older than 30 years. This and next year it was still possible with a new gas condensing boiler, after that you have to plan differently.

Dangerous half-knowledge.
Oil or gas boilers must be replaced after 30 years only if there is a change of ownership (after 2002) AND the boiler does not use low-temperature or condensing technology.
Neither applies here; given the construction year, it is certainly at least a low-temperature boiler and there is no change of ownership.

Let the boiler run until it dies. Afterwards, a condensing boiler with preparation for solar thermal, called a hybrid heating system, will be installed.
As far as I can see, these are still allowed to be installed after 2024. Solar thermal must only be possible, it does not have to be actually installed. It's not as drastic as it sounds.

Just a thought regarding the environment: using things as long as they work is almost always better than replacing them early for supposedly better technology. The production of a new heating system as well as the renovation of the house also causes significant emissions. Heat pumps also cause CO2 emissions during operation, considering the German electricity mix.

Unfortunately, that is a completely wrong assumption! Well/correctly adjusted valves deliver fresh air absolutely inaudibly. Ours, right next to the bed, is not noticeable in terms of volume.

Now you have piqued my interest. Will you tell me what you installed? Until now, I have only found ones with fans and corresponding reports of "noise pollution." Thank you.

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

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

Thank you for knowing the sleeping habits of all Germans. Respect. It's not about the temperature but about the fresh air. When the window is closed, my nose closes and I have to breathe through my mouth. I don't know why that is, but it is very unpleasant.

You're welcome. Not all Germans, but probably 95% of all children... in the world! Because it's not about habit—that's what you're describing—but about the need. And most actually don't need it. The rest—except for very few exceptions—is psychosomatic. Or rather copied from the parents or simply a habit because mom or dad have always opened the window when going to sleep with the words, "otherwise you'll suffocate" or something similar. You have no idea what kind of neuroses parents cause in their children. Although wanting to sleep with an open window at night probably causes relatively little distress. So go ahead and keep doing that, but live with the consequences...