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

Created on: 19 May 2020 13:29
E
exto1791
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.
S
Snowy36
2 Dec 2020 18:14
See post Ypg, who mentioned that sometimes there is a draft on the sofa...

When the mechanical ventilation supplies air at, say, 19°C (66°F) while the indoor temperature is 24°C (75°F), you naturally notice it.
Mycraft10 Dec 2020 15:12
Since questions about long-term tests and real experiences keep coming up, I checked my mechanical ventilation with heat recovery for the first time after 3 years of operation and found no significant dust buildup in the ducts or the unit itself.

Today, 6 more years later (9 years in total), I modified something on the exhaust duct and naturally took another look. Yes, some dust has accumulated in the main exhaust pipe; the yellow-brown area on the left is sealant. However, it’s generally minor amounts and only in the exhaust duct. The supply air ducts still look as if they were new.

Interior view of a round metal duct/ventilation shaft with several circular rings.
K1300S13 Dec 2020 16:42
Do you have no filters in the exhaust vents?
Mycraft13 Dec 2020 16:52
Of course, but these are not 100% airtight, otherwise they wouldn't work, and after 9 years of continuous operation, you still have fine dust in the ducts. I don’t want to imagine what it would look like without an exhaust air filter.
K1300S13 Dec 2020 16:57
In our case, after six years it still looks like new. However, they are plastic pipes.
Mycraft13 Dec 2020 18:30
You are welcome to show your installation. That way, we will have a reference after 6 years.

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