ᐅ KfW 55 – Ventilation System: Yes or No? – Experiences

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.

1. I think so, but I’m not completely sure.
2. If you have the right company that doesn’t take advantage of you, usually the additional costs won’t be higher than the funding. For example, it’s a mystery to me how someone can charge €9,000 for a decentralized system. I’m currently retrofitting one in an apartment. Six units cost me about €2,400, six core drillings cost €475, I’ll do the electrical work myself, but if an electrician connects them, it should be doable for around €500.
That brings us to €3,500. If the builder (who usually has better purchase prices) wants to make some profit on that, it should cost a maximum of about €5,000.
3. Yes, it is! It feels like 95% of people who have one wouldn’t want to do without it anymore. The people who argue against it don’t have one. In new builds, I would always recommend a well-planned, central ventilation system; that also eliminates any problems with “noise.”
4. As I mentioned, for new constructions I would choose a central system. You don’t have a hole to the outside in every room, there’s no fan noise in each room, there is only one unit, and you get better efficiency in terms of heat recovery.
5. Whether it’s KFW55, KFW40, or the energy saving regulations, houses nowadays are airtight. It doesn’t matter if you have a timber frame or solid construction; both are airtight. No air or moisture passes through a 36 cm (14 inch) brick wall with plaster! That means you need to ventilate regularly and thoroughly or install a controlled residential ventilation system.
6. Hard to say... I always keep in mind that companies know the builder receives the KFW funding and then increase the price accordingly. I believe the additional cost difference between meeting the energy saving regulation and KFW55 shouldn’t really be that high. I would NEVER do without a ventilation system in a new build!

The two opinions exist only 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 it’s unnecessary.

This sounds very promising and aligns with many of the ideas I’ve already considered.

Especially regarding the price issue... I also find it completely exaggerated and suspect that developers significantly inflate the prices because they know very well that nowadays everyone wants to take advantage of the subsidies.

I need to make sure I negotiate accordingly.

So, in principle, the ideal solution would be: KfW 55 --> secure a repayment grant of 18,000 (approximately 18k) and then negotiate so that the developer builds the KfW 55 standard for me and installs a proper centralized ventilation system. Everything else probably doesn’t make sense...

What would still be interesting though, if I build to KfW 70 standard, is a ventilation system totally unnecessary then? Would that really be a disadvantage? Just for my understanding. Is this still common practice today?

Assuming the developers are very stubborn about this and I say: forget the subsidy, we build KfW 70 and save all that money while not having any additional technical equipment and just ventilate “manually” as standard.

If you are worried or feel that your provider is overcharging you, you should not proceed with the construction.

Secondly, is it a property developer or a general contractor?

Otherwise, in the first meeting, simply state that you want the KfW 55 standard but are building without a KfW loan.

T_im_Norden schrieb:

If you are worried or think your provider is overcharging you, you shouldn’t proceed with the build.

Also, is it a developer or a general contractor?

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

General contractor, sorry. I unfortunately use the term as if they were the same. But we are building with a general contractor.

Yes, the question is, which provider doesn’t try or actually does that? I’m really curious what the other company will say.

As I said, with this general contractor I don’t know if it’s genuine lack of knowledge or if they are simply calculating aggressively and “overcharging.”

That’s why I’m here to ask how other homeowners have experienced this in similar cases. I think anyone building a solid house faces this issue in some form.

By the way, you shouldn’t expect much from the idea of negotiating.

The companies are all busy and do not need to negotiate.