KfW 55 - Ventilation system yes/no? - Experiences

Hello everyone,

we are currently dealing with the technical aspects of our single-family house.

I haven’t found a thread discussing whether a ventilation system generally makes sense or not. So here is a general discussion thread about it:

At the beginning, we looked at various timber frame construction providers, which made us very sensitive in this area. Of course, a ventilation system is quite important here due to the tighter building envelope, which I can fully understand. However, everything is also marketed accordingly...

Since we are now going to decide on a regional solid house provider, completely different questions arise:

I currently have a detailed offer from a solid construction company:

- 10k extra cost for thermal insulation measures
- 13k extra cost for a central ventilation system or 9k extra cost for a decentralized ventilation system

--> Therefore, the repayment bonus of 18k is of little use to me; on the contrary, I even pay extra for it (of course, I get a “better” house as a result)

Key data:

- Single-family city villa 150m² with basement
- Air-water heat pump
- Building material brick


The questions I now ask myself:

1. Is a ventilation system at all necessary to achieve KFW 55?
2. If yes, does it perhaps make more sense to go for KfW70 and “ignore” the subsidy?
3. Is a ventilation system really that great? You also read a lot about noise, maintenance intensity, etc.
4. If yes, for our building project decentralized or centralized? I have read a lot of good and consistently positive things about decentralized, so centralized seems rather out of the question? Correct or not?
5. Does it still work differently with a KfW55? Do you really have to ventilate every 2 hours? Are there any experience reports?
6. Is the KfW55 surcharge of about 10k without a ventilation system justified? Are the prices for the ventilation systems justified?

I know this is an endless topic of discussion and that there are clearly two opinions here. However, we find it incredibly difficult to make a decision here. Maybe a few discussions and information here will motivate us to be able to decide.

1. I think so, but I’m not entirely sure.
2. If you have the right company that doesn’t take advantage of you, you usually end up with the additional costs not being higher than the subsidy. How anyone can charge €9000 for a decentralized system is a mystery to me, for example. I’m currently retrofitting one in an apartment. 6 units cost me about €2400, 6 x core drilling costs €475, I’m doing the electrical work myself, but if the electrician connects them, that should be feasible for €500. Then we’re at €3500. If the contractor (who, by the way, has even cheaper purchasing prices) wants to make a profit on that, it should cost a maximum of around €5000.
3. Yes, it is! Feels like 95% of the people who have one would never want to be without it. The people who speak against it don’t have one. In new builds, I would always do a well-planned, central ventilation system, then there are no problems with “noise.”
4. As I said, in new builds I would do it centrally. You don’t have a hole to the outside in every room, you don’t have fan noise, you only have one unit and better efficiency in terms of heat recovery.
5. Regardless of KFW55, KFW40 or energy saving regulations. Houses are tight nowadays. It doesn’t matter whether you have a wooden house or solid construction. Both are airtight. No air and therefore no moisture passes through a 36 cm brick wall with plaster! That means you need to ventilate regularly and a lot, or install a controlled residential ventilation system.
6. Hard to say... I always have in mind that companies know exactly that the builder receives the KFW subsidy and then raise the price accordingly. I think the surcharge between energy saving regulations and KFW55 shouldn’t really be that high. I would NEVER do without a ventilation system in a new build!

The two opinions only exist because there are people who have a controlled residential ventilation system (and would never give it up) and people who don’t have one yet and think you don’t need one.

That already reads very well and overlaps with many things I have also already thought about.

Especially the story regarding the price... I also consider that completely exaggerated and suspect that the developers are pushing the prices up enormously because they know very well that nowadays everyone wants to receive the subsidy.

I have to make sure to negotiate accordingly.

So basically the optimal solution would be: KfW 55 --> grab a repayment grant of 18k and then negotiate so that the developer builds KfW 55 for me for 18k and installs a proper central ventilation system. Everything else probably doesn't make sense...
What would still be interesting, if I build KfW 70, is then a ventilation system totally pointless? Would that really be a disadvantage? Just for my understanding. Is that even done nowadays?
Assuming the developers are totally stubborn there and I say: screw the subsidy, we build KfW 70 and save all the money and then also have no additional technical device and ventilate "manually" as standard.

If you are afraid or believe your provider is ripping you off, you should not build with them.

On the other hand, is it now a developer or a general contractor [GU]?

Otherwise, in the first conversation just say that you want KfW 55 level but build without a KfW loan.

If you are afraid or believe your provider is ripping you off, you shouldn’t build with them.

On the other hand, is it now a developer or a general contractor?

Otherwise, just say in the first meeting that you want KfW 55 level but are building without a KfW loan.

GU, sorry. Unfortunately, I use it as if it were the same. But we are building with a GU.

Yes, the question is, which provider doesn’t try or do that? I’m really curious what comes from the other company.

As I said, with this GU I don’t know if it’s actually ignorance or if they are just calculating thoroughly and "ripping off."

That’s why I’m here to ask how other builders deal with this case. I think everyone who builds a solid house faces this in some way.

By the way, you shouldn't expect much from the idea of negotiating. The companies are all busy and don't need to negotiate.