Is residential ventilation only meaningful for 3 bedrooms?

Hello, we are currently planning a new single-family house (9mx9m, 2 floors + basement). We were offered the Energy Saving Ordinance 2009 or optionally Kfw 70 for an extra 13,000 EUR. In addition, a residential ventilation system for the 3 bedrooms on the 1st floor was offered to us at an extra cost of 3,850 EUR (Selfio EuroAir 180m³/h). So far, I have only read about ventilation systems for the whole house; to what extent does it make sense to equip only the bedrooms with the residential ventilation? Are there any disadvantages if not the whole house is connected to the ventilation system? If you build according to KfW 70, you should have a ventilation system for the entire house regarding mold infestation, right? Best regards eineuro

Well, since it is a central system, you can of course install the supply air valves in the bedrooms and the exhaust air valves in the bathrooms/kitchen... and you already have a central system for the whole house and not just for the bedrooms... however, I would take the Euroair 250, the extra cost is laughable but you get a lot more air throughput for it...

Well, and if you are at it anyway, then of course also install supply air valves in the living areas... they don’t cost the earth...

However, careful planning of the whole thing is mandatory... just installing it randomly is rubbish...

In response to my question about a ventilation system for the whole house, I was told that they do not offer that... I suspect they have no idea because the system actually already allows for that.

You really only have all the advantages of such a system if it is set up for the whole house, right?

Does it make sense to possibly outsource such a system?

Yes, it even makes a lot of sense, because then you can find someone who knows their stuff and does this every day...