central vs. decentralized ventilation system

Where do you live that the infrastructure is so bad? Here in the countryside on the Lower Rhine, there are enough craftsmen in every little village. Otherwise, try using portals.

Well, in the Lower Rhine region... Life pulses for us from the Rothaar Mountains. Yes, I had also thought about the portals. But you also need someone who maintains or repairs the thing if there is a malfunction, and the companies around here can also refuse by saying "It's not from us, we won't do anything." I'll probably have to take the cheapest one and try to negotiate with him whether I can get some material myself. But very few agree to that, because they have a mixed calculation.

The major manufacturers all offer maintenance themselves.
My HSLer even prefers that I go directly to the manufacturer and makes his maintenance more expensive on purpose to create the right incentive.
Have the ventilation planned by an independent engineer ([IB Heckmann]) and do it yourself.
It’s not rocket science.
I wouldn’t yet trust myself with a heat pump, but probably with ventilation.

Well, "maintenance." Changing the filter and maybe removing the heat exchanger, flushing it, and putting it back in. Basically, anyone who doesn't gouge their eye out with a screwdriver can manage that. There's no more "maintenance" than that.

But you also need someone who maintains the thing or repairs it if there's a malfunction, and there the

So I see that as the least critical. Maintenance can be done very well by yourself. I wouldn’t expect much repair after the warranty period. But for reasonably clever craftsmen, you should be able to manage everything yourself. Fans are mostly something like ebm motors, which you can also get separately. Sensors and switches might be a bit trickier.