ᐅ Ventilation through wall or ceiling outlets?

We are currently planning the mechanical ventilation system with heat recovery. On the upper floor, our builder is only installing wall outlets for the ventilation and is somewhat reluctant to install ceiling outlets. He argues that each ceiling opening would pierce the vapor barrier twice, and that every bend in the ceiling ductwork tends to increase noise levels. Is this correct? We actually prefer ceiling outlets, as the wall inlets would otherwise have to be placed on the only wall where a wardrobe could fit. Our attic is being converted, meaning the ceiling is not part of the thermal envelope to the outside. Does the vapor barrier still matter in this case?

Additionally, the wall outlets are generally planned quite close to the door (in some cases behind the door). Is this a reasonable approach? When air is being extracted from the bathroom, the fresh air seems to immediately flow out of the room towards the bathroom.

No, it is not practical to plan vents by the door … we had to do this in one room because there was no other option since we also have an exposed roof structure, but if it is not necessary, you avoid it for exactly the reasons you mentioned. In our case, the system was planned by the manufacturer based on the floor plan.

If your ceiling is still dropped below the rafters, the ducts might fit there alongside electrical cables, depending on the actual height of the space in between.
Our setup was as follows: rafters/battens/foil/aluminum profiles/gypsum boards.
We have our outlets for exhaust air on the upper floor installed in the wall, and supply air coming from the floor.

If possible, choose round ducts instead of flat ones (for example, flat ducts can cost three times as much as round ones). However, this depends on the floor construction height.

I planned and installed our controlled residential ventilation system myself (DIY) and we are not yet completely finished. Therefore, I had quite a bit of freedom regarding this topic.

If the pipes for ceiling outlets were located outside the thermal envelope, that would be a real problem (condensation). To be able to provide any suggestions at all, information about the wall and ceiling construction, as well as more general details about the building, would be important.

So, in my case, the pipes on the upper floor are located between the vapor barrier and the drywall, so within the thermal envelope.
The pipes for the ground floor are embedded in the upper floor’s floor structure. Of course, it would have been better to place them in the ceiling cavity (requiring less floor build-up), but my general contractor didn’t agree to that because the structural design was already finalized at the time of the ventilation planning.

My spiral ducts are located outside the thermal envelope, so I carefully insulated them with aluminum-faced mineral wool or Kaiflex. A bit more effort, but it works without any issues.