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.
C
chamäleon
31 Jul 2020 14:47
A question from a layperson:
When an air conditioning system is combined with a controlled mechanical ventilation system, is the air cooled and then distributed throughout the house, or is a parallel system required, like those commonly found in office buildings, where in each room there is a separate split unit in addition to the controlled ventilation air outlet?
Mycraft31 Jul 2020 16:01
@chamäleon

Do you want it to be affordable and fast or complicated and expensive?

To answer your question: Although both devices are responsible for air distribution, their systems are fundamentally very different in their functions.

Therefore: No, with a mechanical ventilation system you can’t really cool the air, even if a cooling cassette is included. But you will always get fresh air.
rick201831 Jul 2020 18:43
Cooling through mechanical ventilation with heat recovery is only possible with very high effort. This no longer corresponds to standard mechanical ventilation with heat recovery.
Tarnari31 Jul 2020 18:54
A colleague told me that in a hotel somewhere in Asia, they don’t have separate heaters anymore but only air conditioning units with heating functions in the rooms. So, one device does it all.

Kind of like, “never mind the electricity costs, as long as it works.”
tomtom7931 Jul 2020 19:03
This happens everywhere, even the French with their cheap nuclear power used to heat like this in the past.

Briefly about controlled residential ventilation: ours is running continuously. Currently, it’s 37°C (99°F) outside, completely darkened indoors, 23°C (73°F) at 6 p.m. Without shading, we easily have 26°C (79°F) or more, and with the door to the garden open, even 30°C (86°F).
Tarnari31 Jul 2020 19:05
tomtom79 schrieb:

This happens everywhere—even the French with their cheap nuclear power used to heat this way in the past.

A brief note on controlled residential ventilation: ours is running constantly. Currently, it is 37°C (99°F) outside, completely dark inside, and at 6 p.m. it’s 23°C (73°F) indoors. Without shading, the temperature easily reaches 26°C (79°F) or higher, and with the door to the garden open, even 30°C (86°F).
Blinds or external venetian blinds?

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