Atypically high offer for ventilation system

So much input, thank you all.

We have informed the BU that we will take a system.

I always wanted one, but there are also many who don’t have one and it doesn’t get moldy.
We are only building according to the Building Energy Act.
And 20k is a lot for ventilation. But I am also afraid of mold and the like.

I hope it was the right decision for you to take one. It will be one from pluggit Avent at 90 percent.

In my enthusiasm for the quality of life I experience every day since the new build, I initially tried to make this gain in quality of life accessible to other people who are currently facing building decisions. The core of the counterarguments was mostly a hurt "I have ventilated like this for 40 years, if I have done it this way for 40 years then it can’t be wrong, so I will continue to ventilate through windows because otherwise I would have to admit something to myself" – and I cannot and do not want to argue against that. That’s why we will probably still see Stone Age ventilation through windows in houses built in 2023 and probably even in 2085. That’s why, even in currently built houses, despite all knowledge, we will continue to waste energy senselessly with every ventilation and rationalize it with a defiant "gas is still cheap!!!111oneone".

How much energy does the ventilation system really save when you factor in the increased living space for laying the pipes, the manufacture, maintenance, and operation of the system?
At some point, I calculated what the hot water costs us and what the actual heat generation costs. I believe the hot water was between 2 and 3 kWh per day. (I would have to check again) If that is the case, heating costs us less than €500 per year. If then a ventilation system should save maybe another 30%, that would be €150 or 450 kWh.
Just the interest on the higher loan for the ventilation system alone is higher than that. It will never pay off financially. And no one knows if even more kWh are burned for the production of the additional materials for raising the house and manufacturing the system than the system then saves.

From my point of view, the ventilation system is purely a comfort feature for dispensing with window ventilation and for air quality.
If you really want to bring in the environmental aspect, then everyone would have to build significantly smaller.

I always find it amusing how on the one hand people get upset about rising construction costs and how much better everything was earlier, but on the other hand easily justify spending €15,000–20,000 (calculating high) for 5–10 minutes of work for ventilation per day. The robot vacuum cleaner or lawn mower probably saves a lot more time for far less money.
On the other hand, everyone runs to the fitness center because they do not move enough.

If you had followed the relevant threads, you would have seen that I never joined in with the "oh god, oh god, building is so expensive, we need to go back to the 70s" but instead say "you get what you pay for."

It is by definition as unnecessary as it is nonsensical to exchange the heat along with the air exchange. Both in summer and winter. The ventilation system automatically switches between heat exchanger and bypass. I always have perfect air 24/7 and to be honest, only since I got used to this have I really noticed how stuffy it often is in apartments with window vents. Just last week my colleague asked me how I actually remove the condensation water that always runs down the inside of the windows – I just said: "What condensation water?" When I return from vacation, it's never stuffy, regardless of the floor. In summer I have it cool inside and the mosquitoes stay outside. When the neighbor plays loud & bad music, I don't care at all, my window is closed after all. My vacuum frequency is significantly lower because there is much less house dust.

That a ventilation system and a lawn mower robot or vacuum cleaner robot exclude each other would be news to me, is there a law about that? If yes, please let me know, I would break it. As I said, the vacuum robot has significantly less to do thanks to the ventilation.

All this can be rationalized away, of course, in case of doubt the (just as nonsensical as omnipresent) romanticizing of work as a free gym comes up. By the same argument, stairs should be replaced by rope ladders and concrete would also be saved.

I know both well enough and next door I still have a house with Stone Age ventilation. There one floor is currently unoccupied and since I haven't had the nerve to drill a hole for the fan in the outside wall, a window remains tilted open 24/7 now – energetically nonsensical as anything, but you can rationalize everything.

Here we can close the topic anyway, the OP has decided on the ventilation system and with that for energy efficiency, quality of life and, by the way, for the resale value of the house.

In retrospect, I have to revise my term "Stone Age ventilation" and sincerely apologize for it.

As is well known, people in our latitudes learned in the early Middle Ages that one can separate smoke and heat from the fire. This naturally also caused a significant increase in construction costs back then – the fact that hardly any complaints about this have survived today is probably only due to the non-existence of internet forums at the time. Of course, it was only in hindsight that people realized this discovery was the main driver for a sharply increased quality of life and life expectancy.

So if we can place the separation of bad air and heat in the early Middle Ages (around 500–1000), then the (rather ineffective but at least problem-recognizing) window rebate ventilation corresponds more to antiquity, and ventilation by tilting the window to the Bronze Age. At least.

The houses from the 2000s were not wrapped up as much as our current ones. We built at the same time

As a rule, airing takes place in passing

but I don’t need more than 1 minute to open and close windows.

Yes, but honestly: one minute is not airing, but simply opening the window.
Advice from the Federal Environment Agency:
In the cold season, depending on temperature and wind, it is sufficient to air 2-3 times a day for about 5 minutes per room with one or several wide-open windows to ensure adequate ventilation.

our uncontrolled residential ventilation called child is chatting again longer at the open door with the neighbor child etc.

That reads cute and you can certainly smile about it, but that's exactly what you want to avoid. Not that the child is chatting, but that energy escapes uncontrollably from the house and you have to heat up again because of it.
And yes, it is hard, and you behave that way yourself, too, but that's one of the no-gos.
If my husband leaves the door open, then I hang a key on the outside and lock the door. I would also make the child move ;-) Because that is not necessary.
If that works for you, then fine. However, I also read in another forum more often that mold is now settling in the house without a ventilation concept. And that's where you can't generalize with the note "it works well without it for us." There are enough who do not want or cannot ventilate regularly and where the house did not come through the construction phase dry as a bone.

How much energy does the ventilation system actually save

I can only speak of life energy. You just don’t have to take care of it, can get ready in the morning and go out the door without worrying, in the evening as well, and you don’t have to let cold air into the house if you don’t want to.

on the other hand, everyone runs to the fitness center because they don’t get enough exercise.

That was my argument against the electrics of my roller shutters. You have to weigh somewhere what else comes on top or what is only built as standard. But I understand your last argument about construction costs: Everyone complains but installs nice-to-haves worth €50,000 if you count the additional sqm for pantry, dressing room, and kids’ bathroom.

If you were following the relevant threads, you would have seen that I never joined in the "oh god oh god building is so expensive, we have to go back to the 70s" chorus but instead say "you get what you pay for". ... That a ventilation system excludes a lawnmower robot or vacuum robot would be news to me, is there a law about that? If so, please let me know, I would break it.

Who has, can... but if the OP is already at the pain threshold, then he just has to decide. Either to give up other amenities or to accept longer terms, which at current interest rates leads to a significantly different price. What was 20k suddenly becomes 40k or more over the term. And if he can no longer afford it, then he can sell his valuable house and look for an apartment with a ventilation system on the housing market.