Planning controlled residential ventilation via local heating / sanitary company

Many heating engineers have their controlled residential ventilation systems planned by the manufacturer, but apparently they do not want to work with private individuals.

I find that absolutely understandable.

There is still a lot that can go wrong during execution, especially if the planning comes from a third party.

The mindset of the OP is probably similar and yes, precisely the reason for not wanting to have this specialist planning done by the general contractor's lackey. Heating, ventilation, and climate control are rather ungrateful fields of activity for the half-knowledgeable. The proportion of houses built with controlled residential ventilation is increasing, but the GCs still seem to have significantly more "experience" with "proven technology."

Personally, I consider planning and execution by two different companies for a small trade like controlled residential ventilation to be unfavorable.
There is still a lot that can go wrong during execution, especially or precisely when the planning comes from a third party.
Isn't there the possibility to find a heating engineer who can do or have the planning done?

I would also prefer if planning and execution came from a single source, but so far I haven’t found a company in the area where I felt there was real expertise regarding ventilation. The standard heating/plumbing contractor from our general contractor does install controlled residential ventilations, but he himself is not convinced of them and rather advised us against it, which is a disqualifying factor for me. Since the installation of controlled residential ventilation is partly carried out by some people here in the forum on their own, I actually thought that at least this part could also be carried out by the standard heating/plumbing contractor of our general contractor. Can so much really go wrong if there is a good plan behind it and everything is specified exactly? Our general contractor was pretty relaxed about it and said that it is actually quite common in larger projects for ventilation planning and execution to be carried out by different companies.

I have already had contact with several heating/plumbing companies, and what really surprises me is that all of them said they only install controlled residential ventilations in about 10% of single-family houses. I actually thought that by now this would be standard in new builds?!

Our general contractor was actually quite relaxed and said that it is often the case, especially in larger projects, that ventilation planning and execution are carried out by different companies.

Yes, in my opinion this is absolutely appropriately seen as a specialist planner issue; and which I also agree with, as one that is best understood by the system developers. The executing companies also like to get the planning directly from the supplier. It hardly matters to the specialist planner from whom they receive their files.

I have already been in contact with several heating/plumbing companies and what really surprises me is that they all stated they only install controlled residential ventilation systems in about 10% of detached single-family homes. I actually thought that this would now be standard in new constructions?!

"Standard" are floor-to-ceiling windows. The client usually thinks technologically in terms of funding and would thus only include controlled residential ventilation where it would raise the overall building equipment package into the next funding level. Controlled residential ventilation is really "in demand" more or less only among pollen allergy sufferers, the other clients apparently regard it somewhat like a kind of shutter motor for the tedious ventilation (and consequently a cutting topic to keep the budget on track).