KfW 55 - Ventilation system yes/no? - Experiences

From an energy perspective, controlled residential ventilation is nonsense. It’s purely about comfort.

Not much can break. And if something does, replacement is cheap. The expensive part of controlled residential ventilation is never the unit itself, but the ducts and installation. Prices range between 7,000 and 20,000 euros depending on region and equipment.

This. I only ever hear from people who have controlled residential ventilation that you apparently save a lot because of it.

I think the original poster’s fundamental idea is wrong. I don’t just install something in my house because it’s subsidized, but because I’m convinced of it. Either I want a central ventilation system or I don’t, I’m happy about the subsidy and gladly pay the difference between the investment and the subsidy. Regarding ongoing costs: Filter change every two months (you can leave them in longer, but due to the property conditions + lots of construction dust in our new development): 20 € per change Electricity cost: 50 W per hour = 438 kWh

I’ll be honest with you: I am 0.0 convinced by an energy-saving house, but what choice do I have nowadays?

Yesterday’s conversation with my general contractor:

- The surcharge for KFW 55 is between 4,000 and 7,000€, he still has to discuss it exactly with the energy consultant
- He “unofficially” does not recommend a ventilation system. The houses they built 10 years ago are almost just as “tight” as the KFW55 houses, so you would have needed a ventilation system back then as well. I shouldn’t panic about mold. Just ventilate normally and that’s no problem. In his 20 years of experience, he hasn’t had a single case of mold in a single-family house. I don’t want to use KfW 55 at all to be energy-efficient here, I actually don’t care about that at all
I actually just want to get the repayment subsidy and that’s it. What is wrong with that basic idea?
He also said that the energy-saving potential is very, very low…

--> Surcharge KfW 55 approx. 5k ---> Repayment subsidy 18k --> that’s a 13k saving. So where exactly is the basic idea wrong here? I’ll skip the whole ventilation system and just ventilate normally?

And that is exactly the point where I said everyone has a different opinion here. Just like the posts before me (“Apparently there are no two opinions here, because only people who don’t have a ventilation system say that”) the same applies to the other side…

My current general contractor installs ventilation systems in maybe 10% of houses, if at all, he said.

Maybe the ventilation system is also marketed extremely heavily, just like the surcharges for KfW 55 etc., just to sell customers an additional technical detail and to push the whole energy-saving story?

Residential comfort, etc… That may be all well and good, but do I really need it? Some here believe you actually NEED it to avoid mold. But I just suspect that in practice this isn’t the case if you ventilate properly and normally.

Maybe I’m wrong here, though?

I had a similar conversation with a general contractor. This whole argument collapsed the second I read the contract – the same "works great without controlled residential ventilation" contractor exempted himself from all damage caused by moisture and instructed the homeowner to ventilate multiple times a day. That is also not consistent. I was allowed to visit an occupied KfW55 without controlled residential ventilation, without prior airing – my first impression was: quite stuffy in here. Is the controlled residential ventilation off? No, there isn’t one installed. Don’t need it, atmosphere like in an old building. Aha. Well, in my old building there are box windows and air always comes in somewhere.

Stop making all these constant claims.

Where exactly did someone 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 tight house must/should be properly ventilated. If you want to sprint through the house four times a day to open and close all the windows, that is perfectly fine. However, comfort and energy savings look different.

No one forces you to build a KFW55 house. There are plenty who don’t do that even today. Everyone can decide that for themselves within the framework of legal requirements. Whether it is wise or not is up to each individual to decide.

Sorry, your posts are really becoming terrible to read. You constantly make things up and assume things because you heard something somewhere….

Somehow you seem to simply ignore most of the statements here.

Oh yes, and many GUs and construction companies often forgo more expensive, modern technology because they simply don’t master it and, of course, are more price-attractive if they install less in your house.

This. I also only hear from people who have controlled residential ventilation that you apparently save enormously because of it. I’ll be honest with you: I am not convinced at all by an energy-saving house, but what else is left for me nowadays? Yesterday’s conversation with my general contractor: - The surcharge for KfW 55 is between €4,000 and €7,000, he has to discuss it precisely with the energy consultant - He “unofficially” does not recommend a ventilation system. The houses they built 10 years ago are almost just as "tight" as the KfW 55 houses; then you would have also needed a ventilation system before. I shouldn’t worry about mold. Just ventilate normally and that’s not a problem. In his 20 years of experience, he has never had mold in a single-family house. I don’t want to use KfW 55 at all to be energy efficient here; I actually don’t care about that at all. I basically just want to get the repayment subsidy and that’s it. What is wrong with that basic idea? Besides, he also said that the energy-saving potential is very, very low... --> Surcharge KfW 55 approx. €5k ---> Repayment subsidy €18k --> makes €13k saving. Where is the basic idea wrong here, please? I leave out the ventilation system and just ventilate normally? And that’s exactly the point where I said everyone has a different opinion here. Just like the posts before mine ("Apparently, there are no two opinions here because only people who do not have a ventilation system say that"), the same applies to the other side... My current general contractor fits maybe 10% of the houses with a ventilation system, if at all, he said. Maybe the ventilation system is also marketed extremely, just like the surcharges for KfW 55 etc., simply to sell the customer another technical detail and to push the whole energy-saving number? Living comfort, etc... Might be all true, but do I really need it? Some here think you actually NEED it in order not to have mold. But I simply suspect that this is not the case in practice if you ventilate properly and normally. Maybe I’m wrong here after all?

In our old apartment (first occupancy after full renovation with ETICS) we always ventilated properly, meaning no tilt ventilation and always with our own front door 2 to 3 times a day with shock ventilation, and still we had mold stains in the corners. And that although no piece of furniture touched the wall directly. So from the outset it was clear: no ETICS and a central ventilation system. Basically, I don’t care whether someone wants, needs, or does not need controlled residential ventilation. Even benefits like “no musty smell in the bedroom after getting up” are not really arguments but first world problems. Based on experience alone, I am pro central controlled residential ventilation even though, looking at the material costs, it is sold/installed overpriced.

Stop making all these constant claims.

Where on earth has anyone said that it is NECESSARY in order not to have mold?
No one denies that you can also ventilate manually!

The question is whether you want to!
A tight house must/should be properly ventilated. If you want to run through the house 4 times a day to open and close all the windows, that’s perfectly fine. But comfort and energy saving look different

No one forces you to build a KFW55 house. There are plenty of people who don’t do that even nowadays. Everyone can decide for themselves within the framework of the legal requirements. Whether it is smart or not is up to each individual to decide.

Sorry, your posts are really becoming horrible to read. You keep putting things together and making all sorts of assumptions because you heard something somewhere....

Somehow you seem to simply ignore most of the statements here.

Oh, and many GUs and construction companies often skip more expensive, modern technology because they simply don’t master it and of course are more attractive price-wise if they install less in your house.

Yes, it is often disputed that it is not possible to ventilate manually, since the DIN standard says that you have to ventilate every 2 hours for 15 minutes.

Manual ventilation doesn’t bother me, I never said that I absolutely want this comfort. I like ventilating and have no problem with it. We don’t even need to talk about energy saving...

Why shouldn’t I build a KfW 55 house??? Again... I get a repayment grant of 18k with an additional cost of about 5k. WHY should I build a Kfw 70 house????

If you want to have the same fresh air in the house without [Kontrollierte-Wohnraumlüftung] as with it, you must ventilate by opening the windows fully every 2 hours, even at night. Do you find that realistically feasible?