ᐅ Is mechanical ventilation with heat recovery necessary for lightweight expanded clay aggregate construction and KfW55 standard homes?
Created on: 19 May 2021 07:34
M
Matthias_1212
Dear forum community,
After finding a plot of land, we now need to specify the technical building services.
We want to build a KFW55 house with a heat pump. So far, so good. After reading extensively in the forum, I was fairly certain that we would need a central mechanical ventilation with heat recovery system (MVHR), since we both work full-time in an office and probably won’t be able to regularly ventilate by opening the windows for air and moisture exchange.
Our builder believes that a central mechanical ventilation system is not necessary with his construction method because he uses expanded clay aggregate blocks. Additionally, he installs a controlled ventilation system integrated in the windows. According to him, a mechanical ventilation system is only installed—if at all—in about one house per year out of more than 100 houses built annually. He thinks the situation would be different with Ytong blocks, where a mechanical ventilation system is always necessary.
If we insist on a mechanical ventilation system, the additional costs would be around €15,000 for the unit (Pluggit) and €8,000 for raising the walls and screed on the upper floor—in total €23,000. From the reports here in the forum, I consider this surcharge to be very high.
Our builder uses expanded clay aggregate blocks. The wall structure is roughly:
- 15cm (6 inches) expanded clay aggregate
- 19cm (7.5 inches) insulation
- vapor barrier and exterior plaster
Total wall thickness: approximately 35cm (14 inches)
I am unable to assess the builder’s statements. Is it true that with expanded clay aggregate blocks a mechanical ventilation system is not needed due to their favorable moisture regulation properties?
I would be very grateful for your help.
Best regards,
Matthias
After finding a plot of land, we now need to specify the technical building services.
We want to build a KFW55 house with a heat pump. So far, so good. After reading extensively in the forum, I was fairly certain that we would need a central mechanical ventilation with heat recovery system (MVHR), since we both work full-time in an office and probably won’t be able to regularly ventilate by opening the windows for air and moisture exchange.
Our builder believes that a central mechanical ventilation system is not necessary with his construction method because he uses expanded clay aggregate blocks. Additionally, he installs a controlled ventilation system integrated in the windows. According to him, a mechanical ventilation system is only installed—if at all—in about one house per year out of more than 100 houses built annually. He thinks the situation would be different with Ytong blocks, where a mechanical ventilation system is always necessary.
If we insist on a mechanical ventilation system, the additional costs would be around €15,000 for the unit (Pluggit) and €8,000 for raising the walls and screed on the upper floor—in total €23,000. From the reports here in the forum, I consider this surcharge to be very high.
Our builder uses expanded clay aggregate blocks. The wall structure is roughly:
- 15cm (6 inches) expanded clay aggregate
- 19cm (7.5 inches) insulation
- vapor barrier and exterior plaster
Total wall thickness: approximately 35cm (14 inches)
I am unable to assess the builder’s statements. Is it true that with expanded clay aggregate blocks a mechanical ventilation system is not needed due to their favorable moisture regulation properties?
I would be very grateful for your help.
Best regards,
Matthias
N
nordanney19 May 2021 16:21Bookstar schrieb:
He just needs to do a bit of research. There’s plenty of information available on this. There’s a reason why most people turn these devices off. They are too expensive for that. Many forum members think these devices are great, especially if a central system cannot be installed. I have one myself and find it good. I don’t know anyone who switches them off. Why would they?
Constant fresh air, affordable, quiet, and eligible for subsidies.
M
Matthias_121219 May 2021 19:36After consulting with our building consultant, we have likely identified the reason for the necessary screed and floor height increase: the ceiling between the ground floor and first floor is only 12cm (5 inches) thick, which apparently leaves insufficient space for the underfloor heating.
I have now asked the developer about the additional costs for increasing the intermediate ceiling by 5cm (2 inches).
Another option would be to completely outsource the mechanical ventilation system and have it contracted externally.
I have now asked the developer about the additional costs for increasing the intermediate ceiling by 5cm (2 inches).
Another option would be to completely outsource the mechanical ventilation system and have it contracted externally.
nordanney schrieb:
Many forum members find these units great, especially when a central system cannot be installed. I have them too and think they are good. I don’t know anyone who turns them off. Why would they?
Always fresh air, affordable, quiet, and eligible for subsidies. Experiences vary a lot. Most people turn these off because of the noise; they are simply very disturbing. The draft is also very unpleasant when sitting nearby. Personally, I found the heat exchanger rather poor as well.
However, I can only speak for Lunos and Meltem. Maybe there are better manufacturers, but I’m not a fan of the technology either. Drilling a large hole into every wall does not make sense to me.
Cleaning also annoyed me. These units get very dirty and require a lot of effort to clean. And it’s not just once, but for every device.
M
Matthias_121220 May 2021 20:49After consulting with the builder, it is not possible to install the ducts within the precast concrete slab. However, they can be placed within the screed insulation. For this, the screed would need to be raised by about 5cm (2 inches). Additional costs amount to 3,000€.
The ceiling height on the upper floor would then be 2.45m (8 feet), which is sufficient according to our regional regulations. This way, we would save the 5,000€ cost for raising the ceiling.
I have now informed the builder that I prefer a Zehnder Q350 instead of the Pluggit AP310. I am curious about the next discussion...
The ceiling height on the upper floor would then be 2.45m (8 feet), which is sufficient according to our regional regulations. This way, we would save the 5,000€ cost for raising the ceiling.
I have now informed the builder that I prefer a Zehnder Q350 instead of the Pluggit AP310. I am curious about the next discussion...
Matthias_1212 schrieb:
I have now informed the builder that I would prefer a Zehnder Q350 instead of the Pluggit AP310. As you know, I’m someone who prefers natural ventilation—so it’s understandable that I’m not particularly eager to dive deep into details about controlled residential ventilation systems. Nevertheless, I suspect that my usual approach could also apply here, and I wouldn’t expect the builder to handle “too many” deviations from the standard. At least, not switching to a different manufacturer. Furthermore, I tend to favor decentralized systems in cases like this, especially if the builder has so far avoided experience with controlled residential ventilation.
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