ᐅ KfW 70 - 36 cm Ytong blocks - Ventilation system

Whether a cavity wall with brick veneer is the best option is hard to say. It always depends on what you want or need to achieve. However, it is certainly one of the more durable types of exterior cladding. It doesn’t necessarily have to be more expensive either. In my case, brick veneer façades were priced about the same as external thermal insulation composite systems (ETICS).

Dali schrieb:
Hello everyone,

we are planning to build a single-family house with the following specifications:
- one and a half stories
- on a concrete slab foundation
- approx. 125 sqm (1,345 sq ft)
- 36 cm (14 inches) Ytong blocks (without additional insulation)
- mineral-based exterior plaster
- KfW 70 standard
- triple-glazed windows
- heating: gas/solar; underfloor heating throughout the house

Regarding a ventilation system, we are undecided about what would be suitable.

Our options are:
- no ventilation system (our builder thinks we don’t need one)
- decentralized ventilation system
- decentralized ventilation system with heat recovery
- centralized ventilation system with heat recovery

We have read a lot in online forums, and the more we read, the more confused and uncertain we become...

Thank you very much in advance for your support!

Hello everyone,

As interesting as this discussion is, the original poster’s question referred to something else. This thread is now already on page 4, and few have addressed the initial question.

Unfortunately, I can’t provide much more input here myself, but I notice that opinions often come down to personal convictions. Views on this differ widely. Ultimately, you will probably have to make your decision based on your gut feeling and your budget.

Maybe this (almost concurrent) thread in this forum might be helpful for you:
https://www.hausbau-forum.de/threads/ventilatoren-fuer-feuchtraeume-und-abluftdunstabzugshaube.9077/

I’ll write my standard response, as I’m convinced that anything other than a central controlled residential ventilation system with heat recovery in new buildings is nonsense...

With decentralized systems, you might save on installation and procurement costs, but you end up with less comfort and higher operating costs afterwards...

Hello everyone,
I think it depends on the new build...
Here is a quote:
"
How a home ventilation system works: Warm air is circulated through ventilation ducts into the house. The system recovers energy from the exhaust air to preheat the incoming cold air. At the same time, used air and the moisture contained in it are extracted. If the heat recovered from the extracted air is not sufficient, additional electric heating is applied.
Disadvantages of a home ventilation system: The drawbacks are clear: it is very expensive to install, requires regular extensive cleaning and maintenance, and consumes additional energy for operation and reheating. There can also be health risks associated with a home ventilation system, as improperly designed heat exchangers, dirty filters, and deposits in the ventilation shafts can lead to contamination with bacteria, viruses, or Legionella, among others. The latter enters the breathing air and causes the potentially fatal Legionnaires’ disease.
To summarize: a home ventilation system is intended to correct a chain of building physics mistakes that have accumulated in the development of low-energy and passive houses. Ultimately, however, it is only another step into a dead end.
In low-energy houses without a home ventilation system, moisture must be removed by airing the rooms several times a day through rapid window ventilation, which causes a lot of heating energy to escape from the house."

The summary basically says it all... unfortunately, we can no longer do without ventilation systems in low-energy and passive houses, as the buildings are sealed as tightly as a plastic bag. I think sometimes less is more... If I can supply the extra energy my building consumes from renewable sources, for example, solar or wood, then that is fine.

Sorry, this might not fully fit here, but when I see some people who want their house to use almost no energy... yet on the other hand, they drive cars with 250 hp.

Mycraft schrieb:


With decentralized systems, you might save on installation and procurement costs, but you get less convenience and higher operating costs afterward...

Higher operating costs? I can't yet speak from personal experience, only based on the consultation I had at the ventilation office. Power consumption for each pair of fans with heat recovery = 12 euros per year. For our 170 sqm (1830 sq ft) we need 3 pairs of fans with heat recovery (so a total of 6 fans) = 36 euros per year for electricity (assuming continuous operation and 30 cubic meters of air exchange directly in the room). The exhaust fans in the wet rooms only run for short periods (triggered by humidity sensors and timers). I'm estimating generously a total of 50 euros per year for electricity (exhaust fans and fans with heat recovery).

Then there is the filter replacement – once per year. Each filter costs about 1.50 euros (for pollen filters 2.50 euros). Usually, the filters can be washed at least once in the washing machine, so often a replacement is only necessary every two years. For simplicity, assuming one filter change per year, with 6 fans that’s 9 euros (15 euros for pollen filters).

As I said, I’m just relaying the information from the consultation. However, I have seen similar figures regarding electricity costs from other users online.

Other operating costs? I really can’t think of any at the moment.

I might be wrong @Mycraft, but you mentioned higher operating costs for the central system in the other thread. That’s why I’m asking so specifically – I’m interested in the differences, advantages, and disadvantages of both systems (although we have already decided in favor of decentralized).

The electricity costs are comparable for both options... the central system has only 2 fans... whereas the decentralized system has 10 or more... so, overall, the values end up being similar.

However, with the decentralized system, you need more filters and have to clean the units more frequently because the heat exchangers, etc., clog up much faster than in central systems... Each fan also requires a separate condensate drain and must be installed completely sealed into the wall... and having 10 holes in the wall increases the risk of errors significantly...

Additionally, there is the factor that the fans can occasionally fail... and not always within the warranty period... of course, the seller says "They last forever," but that is not the case... and then you have to spend a bit more money... and so on.