Planning controlled residential ventilation via local heating / sanitary company

Hello, after a long back and forth I have almost convinced my wife that we need a controlled residential ventilation system. Her main concerns are the dry air in winter and the noise development. Today we had a conversation with the local heating/plumbing company that works with our general contractor. Unfortunately, the plumber rather reinforced my wife's concerns and said that dry air is indeed quite a big problem and, regarding my objection about the possibility of an enthalpy heat exchanger, he said that it would hardly bring anything and would just cost money.

My biggest fear is actually a poorly planned controlled residential ventilation system (noise, drafts, etc.) and I have the feeling that the chances with the company are not small. We were offered a Helios Controlled Residential Ventilation EC 370w. As far as I have found out about this device, it seems to be one of the older models and rather undersized for our house (202 sqm on 2 full floors). When I asked, the plumber said that this had enough leeway and that we definitely would not hear anything. The planning of exhaust and supply air etc. is done by the local company. According to the plumber, they have a lot of experience with controlled residential ventilation systems and there have never been any problems with noise etc. so far. I had understood that the planning is usually done by the large companies (Zehnder, Helios, etc.) and only the installation is then done by the heating/plumbing company, which I would definitely prefer.

How was it for you? Who planned the system? Does anyone know the Helios device or is it correctly dimensioned for our house if you want to avoid noise?

Last house central controlled residential ventilation - planned by the heating engineer (whatever about that - doesn't matter). Plot. You don’t have any noise or drafts with a central controlled residential ventilation. So no worries.
You can get dry air in winter. But you also have that without controlled residential ventilation with pure heating air - just a few % more humidity. Enthalpy exchangers already help. Plants etc. as well.
I can’t tell you anything about Helios from my own experience. But in my opinion, it’s also not bad if the device is older. Basically, a central fan blows air in or sucks it out. That is far from high-tech.
Currently, I have a decentralized ventilation installed in my new house. It is more noticeable (by noise), but even here you don’t feel any draft (except at full power).
My conclusion: Never again without controlled residential ventilation. Always fresh and pollen-free air in the house.

Thank you for the response! The issue with dry air is actually the only relevant point for me against a controlled residential ventilation system. So far, I thought that the dryness problem could be well solved with an enthalpy exchanger. What does such an exchanger really provide? Almost everyone in our family actually has problems with the upper respiratory tract, so I definitely want to avoid dry air. Does anyone know the Helios 370 and isn't the device actually too small for our house?

An enthalpy heat exchanger does not drain condensate, so it returns all the condensate generated (several liters per day) back to the supply air. It works so well that after two winters I still have trouble keeping my building dry and increasingly rely on window ventilation.

Especially if you don't want dry air, a controlled residential ventilation system with EWT is recommended. All other types of ventilation dry the air much more. The alternative to controlled residential ventilation is not to not ventilate, but to ventilate through windows. Here the loss of moisture is significantly higher. There is surely somewhere a calculation example where some smart person has already calculated this.

If the heating engineer says that an EWT is useless, I would look for another heating engineer and another provider for the ventilation system.

You don't have any noise if the system is properly planned. This includes, for example, two instead of one air outlet in the bedroom, a slightly oversized ventilation unit, silencers, and corresponding flow-optimized valves.

I have no experience with Helios but I would personally recommend Zehnder.

Hey, my construction has been bone dry since winter (CM measurement screed & humidity with hygrometer). You always read that a new building can't be dried out for a year. Where does the discrepancy come from? Now I'm afraid that moisture has been trapped somewhere and can't escape, but over time damage will go unnoticed somewhere. Until I suddenly die from mold exposure or dry rot grows out. Can that be possible?

Tell me, my construction has been bone dry since winter (CM measurement screed & air humidity with hygrometer). You always read that you can't get a new building dry for a year. Where does the discrepancy come from? Now I'm afraid that moisture has been trapped somewhere and can't get out, but over time an unnoticed damage develops somewhere. Until I suddenly die of mold exposure or the house fungus grows out. Can that be?

I'm not an expert, but I consider that unlikely.
The interior plaster has a strong capillary effect. As soon as it comes into contact with moisture anywhere, it draws it over a large area into the plaster and releases it into the room air. There are certainly differences whether it's gypsum or lime plaster, but I consider it unlikely that it "traps" moisture. Did you use a mineral paint for the interior coating?

With me, it rained a lot during the shell construction and the brick wall stood in water. According to the manufacturer's statement, that's no problem as long as it doesn't freeze or rain directly into the brick from above. This water certainly takes its time until it is released into the room air.