Experiences with central exhaust system without heat recovery

I will answer zizzi's questions. Yes, we have underfloor heating. No, there was no choice, as this system is the standard of my GU. Controlled residential ventilation was then an extra cost. Without any ventilation, he only does it upon express request and under protest. Karsten

Currently living in a KW 70 house without a ventilation system. Our humidity is also at 30-40%. The system would not make it worse.

So we are also facing the decision and have sought support from the energy consultant (KFW application/calculation).
Quote: Underfloor heating provides long-wave thermal radiation, which is designed to warm building structures and objects to ensure comfortable living.
Heat recovery from air that is not highly energy-containing is then not always sensible. A counter-calculation justifying the additional costs of the central system with heat recovery is not necessarily given for the initial situation of setting KfW55 as a target.
For various reasons, we have now decided on central exhaust air with decentralized fresh air inlets in the window.
There should be no talk of drafts.

This is just our experience so far, which is awaiting implementation this year.

So we are also facing the decision and have had support from the energy consultant (KfW application/calculation).
Exact quote: Underfloor heating provides long-wave thermal radiation, which is designed to warm the building structure and objects to ensure comfortable living.
Heat recovery from air that does not contain much energy is then not always sensible. A counter-calculation that justifies the additional costs of central systems with heat recovery is not necessarily given for the starting point of setting KfW55 as the target.
For various reasons, we have now decided on central exhaust air with decentralized inlet air units at the window.
Drafts are out of the question.

This is just our experience so far, which is awaiting realization this year.

Probably we consulted with the same person [emoji6]
I got the same information from our contact person (architect) who worked for years as an energy consultant. We want/will build KfW70 with underfloor heating. He said that with normal ventilation we will have no mold problems. I think central exhaust system + decentralized inlet air is an option where you get a bit more comfort and fresh air for little money. My only fear is drafts caused by inlet air, but Nordlys reassured me with his experience.

Hello Zizzi and Steija1,
we are currently considering the same things you were thinking about 2 years ago and I would be very happy to hear about your experiences with the central exhaust system. When we were dealing with prefabricated houses, we had already decided against a controlled residential ventilation system (To everyone whose fingers are twitching now: We don’t need to discuss that here anymore ). We are now building with Ytong/mineral wool insulation/brick facing and underfloor heating. According to our construction company, there have never been mold problems even without ventilation (??). And we also reach KfW55 without controlled residential ventilation (among other things because of the combined heat and power plant). The house is already energetically calculated this way and construction has already started. A friend of ours, who is a dedicated installer (and who wouldn’t get a contract for this construction site anyway, so he has no conflict of interest), talked us into the conscience that we absolutely need some form of automatic ventilation and has now brought this solution into play. The central exhaust system seems to us to be a conceivable alternative. At least the costs are significantly lower and the sometimes discussed contamination and cleaning of supply air ducts is eliminated. What seems important to me is that the exterior vents can be completely closed if necessary (e.g. in case of warning about toxic gases or similar, or if you don’t get along with the possible draft), that the sound insulation is good and it would be great if a filter could be installed.
Unfortunately, it is really difficult to find information and experience regarding this form of ventilation. Therefore, it would be incredibly valuable to hear something from you. Has this model proven itself for you? What are the disadvantages in practice? Cold draft, flow noises, noise disturbance from outside due to window ventilators? How high did the doors have to be above the floor so that the air exchange works?
If I understand correctly, the energy standard is not worse with the central exhaust system than it is calculated now with conventional window ventilation, right? We wouldn’t want to risk our KfW loan + funding.

Hi, so we have now been living in the house for 1 1/2 years and I can only share my experiences, which have probably already been hotly discussed here, but it wasn’t about the fundamental question controlled residential ventilation vs...

So we have the central exhaust from all wet rooms and the kitchen, which was very important at the beginning, because the house quickly created high humidity levels due to moisture from the construction. This naturally decreases over time and is no longer a factor you directly notice. Still, I would say that without the system it becomes very difficult in the long term due to the airtight construction, even if you are away for a few days. The exhaust is controlled via my KNX system and thus not continuously running, but on warm days especially at night running at full power to get cool air into the house. In winter then dosed to create the necessary air exchange. No big stress with airing etc.. and yes, we left out a controlled residential ventilation system during construction for cost reasons (about 5000€ more) and I would say in retrospect the decision was okay. Sure, you have worse efficiency, but you first have to recover that sum, the calculation might be somehow representable over decades (if at all). What that means for your Kfw loans should be something the energy consultant can tell, as he makes the overall calculation from all components that play a role within the Energy Saving Ordinance.

Best regards,

Jan