Which ventilation system for old building renovation

Hello,

we have just bought an old building (1968 single-family house, fully basemented, 150m² living space). We will insulate it and upgrade the windows to KFW standard. The house has two children's rooms, two offices for home office, two toilets, a large bathroom, as well as kitchen and living room.

The question is what to do about the ventilation. Only window ventilation is out – we currently have that in our apartment (built in 2011, extremely airtight, but only window ventilation) and find it extremely unpleasant.

Currently, we are hesitating between:

1. Decentralized ventilation. It is unclear to me in how many rooms we should install fans here? Kitchen, the three WCs/bathrooms, bedroom and children’s rooms? What about the offices?

2. Exhaust air system for the bathrooms and kitchen. Supply air flaps in the other rooms. This would have the advantage of only minimal additional effort, since all bathrooms and the kitchen border the chimney, which still has space for ventilation pipes. And the core drillings for the supply air openings, but those are no big problem.
I would like to place the system in the basement, since there is enough space, electricity and so on. The attic is bad, there is no power, frost protection would have to be added, and it is difficult to access.

3. Exhaust air system like No. 2, but with heat recovery.

I would find a complete supply and exhaust air system nice, but my problem is the very high price and also the enormous effort to install the pipes somewhere. So that’s rather out.

Where I am currently somewhat desperate is finding good information about what the variants really ultimately cost, what one can do well oneself, and what the pros and cons of the different products are. I find it all opaque and difficult. Do you have any opinions or tips on this?

If a room only has supply air and the door is closed, you will eventually have overpressure there. That will become noticeable. I happen to know this because it was like that at an acquaintance’s place, but the system was just incorrectly set up. If the doors have ventilation slots, it would work. But that is, firstly, expensive because of new doors and secondly, probably especially bad for sound insulation.

Inform yourself about the possibilities of supplying cooled fresh air. I took a closer look at that for my project and found some interesting systems.

What else comes to mind is, are you even allowed to install the ventilation ducts in the chimney? You wouldn’t want to blow exhaust gases into the rooms.

Decentralized systems, probably best one per room. But I’m always skeptical about the noise generation.

Maybe you have a ventilated facade; if properly insulated, you could also lay the pipes there and thus easily reach every room from the outside. But I can’t say if that would be ideal.

A central system doesn’t have to be expensive; you can do a lot yourself (almost everything).

Hello Garfunkel,
thank you very much for your reply!
The pipes in the chimney should not be a problem, we have several flues in the chimney and they are separated from each other. It is just a bit unclear whether the thick pipes will fit in there at all.

Unfortunately, we don't have a ventilated facade - everything is solid.

Yes, it really isn't difficult - only the planning is annoying and I have found very few good contacts there so far.
At the moment, I am leaning either towards installing two to three Blumartin Freeair units (1 ground floor, 2 upper floor) or one central unit in the basement, if I can get the pipes somehow into all rooms without having to lower the ceiling everywhere (I can get to the upper floor from the attic, but the ground floor is problematic).