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

Created on: 19 May 2020 13:29
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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.
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Bookstar
27 May 2020 16:05
From an energy perspective, controlled residential ventilation is pointless. It’s purely about comfort.

There isn’t much that can go wrong with it. 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, depending on the region and features.
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dhd82
27 May 2020 16:37
I think the original idea of the OP is fundamentally wrong.
I don’t install something in my house just because it is subsidized, but because I am convinced of it.
Either I want a centralized ventilation system or I don’t; I appreciate the subsidy and am happy to cover the difference between the investment and the subsidy.
Regarding ongoing costs:
Filter replacement every two months (they can be left in longer, but due to the site conditions and a lot of construction dust in our new development): 20 € per replacement
Electricity consumption: 50 W per hour = 438 kWh
tomtom7927 May 2020 19:20
dhd82 schrieb:

Filter replacement every two months (you can leave them in longer, but due to the site conditions + a lot of construction dust in our new development): 20 € per replacement
Electricity costs: 50 W per hour = 438 kWh
I can cut the filter mats myself, then I pay a maximum of 20-30 Euro for G5 filters in about 2 m² (21.5 ft²), and they last 2 years.
Mycraft27 May 2020 19:54
Same here... why should you pay ten times more when the mat stays the same. But yes, I have also bought pre-cut pieces before, but only because they were priced about the same as the material sold by the meter.
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dhd82
27 May 2020 20:49
Thanks for the tip, I will look into making the filters myself.
Do you also do this for the supply air filter?
My system has two filters: a G4 filter for the exhaust air (mat) and an F7 filter for the supply air (filter box).
AxelH.27 May 2020 22:21
We are using the Vitovent 300 W from Viessmann. A pack of 20 G4 filters costs 30 euros. They come ready-to-use and cut to size. This is more than enough for over 2 years. So, filters are definitely not a major cost factor.