Hello everyone,
We are currently starting to deal with the technical aspects of our single-family home.
I haven’t found a thread discussing whether a ventilation system generally makes sense or not. So here is a general discussion thread on the topic:
At first, we looked into various timber frame construction providers, which made us quite sensitive in this area. Naturally, a ventilation system is quite important due to the tighter building envelope, which I can completely understand. However, everything is also marketed accordingly...
Since we have now decided to go with a regional solid construction company, completely different questions arise:
I currently have a detailed offer from a solid construction company:
- $10,000 additional cost for thermal insulation measures
- $13,000 additional cost for a central ventilation system or $9,000 additional cost for a decentralized ventilation system
--> So the repayment subsidy of $18,000 is of little use to me; on the contrary, I am even paying extra for this (of course, I get a “better” house in return).
Key Data:
- Single-family home city villa, 150m² (1,615 ft²) with basement
- Air-to-water heat pump
- Building material: brick
The questions I am now asking myself:
1. Is a ventilation system even necessary to achieve KfW 55 standard?
2. If yes, would it maybe make more sense to go for KfW 70 and forget about the subsidy?
3. Is a ventilation system really that great? There are many reports about noise, high maintenance, etc.
4. If yes, in our building project would a decentralized or central system be better? I have read a lot of positive things about decentralized systems, so central ones might not be an option? Is that correct or not?
5. Is it even possible to reach KfW 55 standard otherwise? Do you really have to ventilate every 2 hours? Are there any experiences?
6. Is the additional $10,000 cost for KfW 55 without a ventilation system justified? Are the prices for the ventilation systems justified?
I know this is an endless debate and there are clearly two opinions here. However, we find it really difficult to make a decision. Maybe a few discussions and information here will help us make up our minds.
We are currently starting to deal with the technical aspects of our single-family home.
I haven’t found a thread discussing whether a ventilation system generally makes sense or not. So here is a general discussion thread on the topic:
At first, we looked into various timber frame construction providers, which made us quite sensitive in this area. Naturally, a ventilation system is quite important due to the tighter building envelope, which I can completely understand. However, everything is also marketed accordingly...
Since we have now decided to go with a regional solid construction company, completely different questions arise:
I currently have a detailed offer from a solid construction company:
- $10,000 additional cost for thermal insulation measures
- $13,000 additional cost for a central ventilation system or $9,000 additional cost for a decentralized ventilation system
--> So the repayment subsidy of $18,000 is of little use to me; on the contrary, I am even paying extra for this (of course, I get a “better” house in return).
Key Data:
- Single-family home city villa, 150m² (1,615 ft²) with basement
- Air-to-water heat pump
- Building material: brick
The questions I am now asking myself:
1. Is a ventilation system even necessary to achieve KfW 55 standard?
2. If yes, would it maybe make more sense to go for KfW 70 and forget about the subsidy?
3. Is a ventilation system really that great? There are many reports about noise, high maintenance, etc.
4. If yes, in our building project would a decentralized or central system be better? I have read a lot of positive things about decentralized systems, so central ones might not be an option? Is that correct or not?
5. Is it even possible to reach KfW 55 standard otherwise? Do you really have to ventilate every 2 hours? Are there any experiences?
6. Is the additional $10,000 cost for KfW 55 without a ventilation system justified? Are the prices for the ventilation systems justified?
I know this is an endless debate and there are clearly two opinions here. However, we find it really difficult to make a decision. Maybe a few discussions and information here will help us make up our minds.
Bookstar schrieb:
From an energy perspective, controlled residential ventilation systems are nonsense. It's purely about comfort.
There isn’t much that can break. And if something does, replacement is inexpensive. The costly part of controlled residential ventilation is never the unit itself, but the ductwork and installation. Prices vary between 7,000 and 20,000 euros (approximately 7,500 to 21,500 USD), depending on region and equipment.This. I only hear from people who have a controlled residential ventilation system that it apparently saves a lot of energy.
dhd82 schrieb:
I find the original poster’s basic idea wrong.
I don’t install something in my house just because it’s subsidized, but because I’m convinced it’s beneficial.
Either I want a central ventilation system or I don’t. I appreciate the subsidy and gladly pay the difference between the investment and the subsidy.
Regarding ongoing costs:
Filter replacement every two months (you can leave them in longer, but due to plot conditions plus a lot of construction dust in our new development): 20 € per replacement (about 21.50 USD)
Electricity costs: 50 W per hour = 438 kWh To be honest with you: I’m not convinced at all about an energy-saving house, but what else can I do nowadays?
Yesterday’s conversation with my general contractor (GC):
- Additional cost for KfW 55 standard is between 4,000 and 7,000 euros (approximately 4,300 to 7,500 USD), he needs to discuss details with the energy consultant
- He “unofficially” does not recommend a ventilation system. The houses they built 10 years ago are almost as airtight as the KfW 55 houses, so they would have needed a ventilation system back then as well. I shouldn’t worry about mold. Just ventilate normally and that’s no problem. In his 20 years of experience, he hasn’t seen mold in a single-family home so far. I don’t want to aim for KfW 55 for energy reasons—I honestly don’t care about that.
I mainly want to get the repayment subsidy and that’s it. What’s wrong with that idea?
He also said the potential for energy savings is very, very small.
--> Additional cost KfW 55 approx. 5,000 euros (about 5,400 USD) --> Repayment subsidy 18,000 euros (about 19,400 USD) --> that’s a 13,000 euro (about 14,000 USD) saving. Where exactly is the flaw in this line of thinking? I’ll skip the ventilation system and just ventilate normally?
And that’s exactly where I said everyone has a different opinion here. Just as the previous posts ("Apparently there are no two opinions here because only people without a ventilation system say that") applies the same to the other side...
My current GC installs ventilation systems in maybe 10% of the houses, if at all, he said.
Maybe the ventilation system is marketed very aggressively, just like the extra costs for KfW 55, to sell customers an additional technical feature and push the whole energy-saving topic?
Comfort, etc... maybe all that’s true, but do I really need it? Some here believe it’s actually necessary to avoid mold. But I just suspect that this is not the case in practice if you ventilate properly and normally.
Maybe I’m wrong here?
I had a similar conversation with a general contractor (GC). Their entire argument fell apart the moment I read the contract – the same GC, who claimed "works perfectly fine without mechanical ventilation," clearly excluded all damage caused by moisture and required the homeowner to ventilate multiple times a day. This approach is not consistent.
I was allowed to visit an occupied KfW55 building without mechanical ventilation, where no ventilation had been done beforehand – my first impression was: the air felt quite stale. Is the mechanical ventilation off? No, there isn’t any installed. It’s not needed, the atmosphere is like in an older building. I see. In my old building, there are box windows and air always comes through somewhere.
I was allowed to visit an occupied KfW55 building without mechanical ventilation, where no ventilation had been done beforehand – my first impression was: the air felt quite stale. Is the mechanical ventilation off? No, there isn’t any installed. It’s not needed, the atmosphere is like in an older building. I see. In my old building, there are box windows and air always comes through somewhere.
Stop making all these constant claims.
Where exactly did anyone say that it is REQUIRED to avoid mold?
No one denies that you can also ventilate manually!
The question is whether you want to!
A tightly sealed house must/should be properly ventilated. If you want to go through the house four times a day to open and close all the windows, that’s perfectly fine. However, comfort and energy savings look different.
No one is forcing you to build a KFW55 house. There are plenty of people who still don’t do that nowadays. Everyone can decide for themselves within the framework of legal requirements. Whether it is wise or not is up to each person.
Sorry, your posts are becoming really difficult to read. You constantly make assumptions based on things you’ve heard somewhere....
Somehow, you seem to completely ignore most of the points made here.
Oh, and many general contractors and construction companies often skip more expensive, modern technology because they simply don’t master it and, of course, it’s more financially attractive to install less in your house.
Where exactly did anyone say that it is REQUIRED to avoid mold?
No one denies that you can also ventilate manually!
The question is whether you want to!
A tightly sealed house must/should be properly ventilated. If you want to go through the house four times a day to open and close all the windows, that’s perfectly fine. However, comfort and energy savings look different.
No one is forcing you to build a KFW55 house. There are plenty of people who still don’t do that nowadays. Everyone can decide for themselves within the framework of legal requirements. Whether it is wise or not is up to each person.
Sorry, your posts are becoming really difficult to read. You constantly make assumptions based on things you’ve heard somewhere....
Somehow, you seem to completely ignore most of the points made here.
Oh, and many general contractors and construction companies often skip more expensive, modern technology because they simply don’t master it and, of course, it’s more financially attractive to install less in your house.
exto1791 schrieb:
This. I only hear from people who have a mechanical ventilation system with heat recovery that it apparently saves a lot of energy.
Honestly, I am not convinced at all about energy-efficient houses, but what choice do I have nowadays?
Yesterday’s conversation with my general contractor:
- The extra cost for KfW 55 is between 4,000 and 7,000 euros (about 4,800 to 8,400 USD), he will need to discuss the details with the energy consultant
- He “unofficially” does not recommend a ventilation system. The houses they built 10 years ago are almost as airtight as the KfW55 houses, so a ventilation system would have been needed back then too. He told me not to worry about mold. Just ventilate normally and it’s not a problem. In his 20 years of experience, he has never seen mold in a single-family house. I do not want to use KfW 55 to be energy-efficient, that doesn’t really interest me. I just want to get the repayment subsidy and that’s it. What is wrong with this basic idea?
He also said that the potential energy savings are very, very small.
--> Extra cost for KfW 55 approx. 5,000 euros (about 6,000 USD) ---> Repayment subsidy 18,000 euros (about 21,600 USD) --> that’s a 13,000 euro (about 15,600 USD) saving. Where exactly is the problem with this reasoning? I skip the ventilation system and just ventilate normally?
And this is exactly the point where I said that everyone has a different opinion here. Just like the previous posts (“Apparently there are no two opinions here because only people without a ventilation system say that”), the same applies to the other side.
My current general contractor installs mechanical ventilation systems in maybe 10% of the houses, if even that, he said.
Maybe the ventilation system is marketed extremely heavily, just like the extra costs for KfW 55 etc., simply to sell an additional technical feature and push the whole energy-saving idea?
Comfort and so on… that may be true, but do I really need it? Some say it is actually NECESSARY to avoid mold. But I simply suspect that this is not the case in practice if you ventilate properly and normally.
Maybe I am wrong?In our old apartment (first occupancy after major renovation with external thermal insulation composite system – ETICS), we always ventilated properly—no tilt ventilation but rather quick airing 2 to 3 times a day with our own front door—and still had mold spots in the corners. And that was despite no furniture touching the walls. So right from the start it was clear: no ETICS and a central mechanical ventilation system.
Basically, I don’t care whether someone wants, needs, or does not need a mechanical ventilation system with heat recovery. Benefits like “no musty smell in the bedroom after waking up” are not really valid arguments, just first-world problems. Based on experience alone, I am in favor of a central mechanical ventilation system with heat recovery, even if the material costs for it are overpriced when you look at them.
Specki schrieb:
Stop making constant claims.
Where exactly did anyone say that it is REQUIRED to avoid mold?
No one denies that you can also ventilate manually!
The question is whether you want to!
A well-sealed house must/should be properly ventilated. If you want to walk through the house four times a day to open and close all the windows, that’s perfectly fine. However, comfort and energy savings look different.
No one is forcing you to build a KfW 55 house. There are plenty of people who don’t build one even today. Everyone can decide this for themselves within the legal requirements. Whether it is wise or not is up to each individual.
Sorry, your posts are really becoming painful to read. You keep putting things together and making assumptions because you heard something somewhere....
It somehow seems like you simply ignore most of the statements here.
Oh, and many general contractors and construction companies deliberately avoid more expensive, modern technology because they simply don’t master it and, of course, are more attractive price-wise when they install less in your house.It is often disputed that manual ventilation is not possible, since the DIN standard requires ventilation every two hours for 15 minutes.
Manual ventilation is not a problem for me; I never said I necessarily want this comfort. I like ventilating and have no issues with it. We don’t even need to talk about energy savings...
Why shouldn’t I build a KfW 55 house??? Once again... I get a repayment bonus of 18,000 with an extra cost of about 5,000. WHY should I build a KfW 70 house???
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