Decentralized vs. Central Controlled Residential Ventilation? Points for KfW House Calculation

A lovely good morning to everyone,

we, 30 years old and 27 years old, are currently planning our 2 full-storey house as a KfW 70 house with ~140sqm. Through the forum and various sales talks, we have become aware of the fact that the new houses, especially as KfW, are quite airtight.

Now the question arises for us about ventilation. The seller offered us an inverter controlled residential ventilation system for just under 7,730.00 EURO. After some research here in the forum as a guest and also via Google, I came across the fact that there are also central controlled residential ventilation systems. This seems to be the better option for us because you don’t have the noisy fans in every room, as is the case with a decentralized system. In addition, you don’t have holes in the insulated walls in every room.

In advance, I have looked at the Zehnder ComfoAir 350 system as a central controlled residential ventilation. There are good opinions about it and it is cheaper compared to a Hoval HomeVent RS 250. Now the question arises for me whether this is the right choice or whether one can do without a controlled residential ventilation system in a KfW70 house?! I am also undecided, if a controlled residential ventilation system is necessary, whether it should be a decentralized or central controlled residential ventilation version?.. There is so much to consider and especially the sellers only tell you what you want to hear, partly wanting to get rid of their stuff.

Furthermore, I wonder if we can improve the rating of a KfW house with a controlled residential ventilation system with heat recovery, i.e. without controlled residential ventilation with heat recovery KfW70, with controlled residential ventilation + heat recovery = KfW 55?

As primary energy, we use district heating, which the city generates with a primary energy factor of 0.11. No solar, no geothermal etc.

I would be happy to receive numerous answers.

Best regards
mirage

Hi Mirage, a few remarks from a layperson: - the KfW calculation should improve significantly - decentral only makes sense if you want to ventilate individual (few) rooms selectively - it becomes more comfortable and better with a central controlled residential ventilation system - however, you have pipes throughout the house, costs, etc. Best regards

Tomorrow PeterXYZ,

ah, yes, the decentralized for a few rooms makes sense. Our developer, whom we are considering more closely, uses prefabricated concrete parts that are cast in a factory according to the plan. Does that make a difference when planning a central controlled residential ventilation system?

Has anyone had experience with this?

Regards
mirage

Hello,

we, 30 years old and 27 years old, are currently planning our second full-story house as a KfW 70 house with ~140 sqm. Through the forum and various sales talks, we became aware of the fact that the new houses, especially as KfW, are quite airtight.

That is so.

.... This seems to be the better option to us, since you don’t have the noisy fans in every room, as is the case with a decentralized system. Besides that, you don’t have holes in the insulated walls in every room.

The fans of a decentralized ventilation system are anything but noisy; who says such a thing?

I initially looked at the Zehnder ComfoAIR 350 system as a central controlled residential ventilation. There are good opinions about it and compared to a Hoval HomeVent RS 250 it is cheaper.

First of all, I can hardly imagine that you will have any significant influence on the brand to be installed; every provider has their preferences/contracts. However, the important thing is, in any case, that the controlled residential ventilation is adapted to the needs of the house and not based on the provider’s preferences.

Now the question arises whether it is the right choice or if one can do without a controlled residential ventilation in a KfW70 house?!
I am also unsure, if a controlled residential ventilation is necessary, whether it should be a decentralized or central controlled residential ventilation version?.. You have to consider so much and especially the sellers only tell you what you want to hear, partly wanting to get rid of their stuff. Furthermore, I wonder if we can improve the rating of a KfW house with a controlled residential ventilation with heat recovery, i.e. without controlled residential ventilation with heat recovery KfW70, with controlled residential ventilation + heat recovery = KfW 55?

The decision for a controlled residential ventilation system with or without heat recovery should never be made based on a few - negligible - values for the calculation of the Energy Saving Ordinance; that is all smoke and mirrors and takes place almost exclusively on paper.

Deciding on a central controlled residential ventilation always makes sense; the heat recovery is not necessarily required because it costs more than it makes sense. You have a high gain in comfort and especially in the first years - if the system was properly installed - no risk of mold due to the drying out of the house. Furthermore, you can leave the house to itself anytime with peace of mind - for example, on vacation - without asking family or neighbors to ventilate the house; if your flowers are planted in Seramis, you also don’t need anyone to water the flowers.

Best regards

Hello,

...Choosing a central controlled residential ventilation system always makes sense; heat recovery is not necessarily required, as it costs more than it is worth.

I see that a bit differently. The true value of a controlled residential ventilation system is measured by comfort and controlled ventilation. The price difference between a central controlled residential ventilation system without heat recovery and one with heat recovery is not as significant as is often assumed.
The "cooler" the climate location, the more effective the controlled residential ventilation system with heat recovery. Furthermore, it always makes sense to consider the controlled residential ventilation system in connection with the other system technology. The controlled residential ventilation system with heat recovery partially and significantly reduces heating loads, so that, for example, when a heat pump is used as a heat generator, often a unit with a smaller capacity can be chosen. This saves several thousand €, especially with a brine heat pump, since not only the unit but also the source becomes cheaper. Here, the additional expense for heat recovery often disappears, and it results in not only an investment saving.
Best regards.

Hi,

many thanks for your numerous responses. It is as Bauexperte already suspected. We are both fully employed, I leave the house at 5:00 a.m. and my partner at 5:30 a.m., and we are back home around 4:20 p.m. I am a civil servant with 41 hours per week :-( and she works in the public service, so we are never home earlier.

From our developer, we have more or less free rein; if I say I want the Zehnder ComfoAir 350 enthalpy, then it will be installed...

As confirmed above, we fear that we will not take ventilation very seriously because no one is home all day anyway, at least not yet. And when I think about ventilating completely twice a day, I do that for the first three weeks after moving in; after that, you just don’t feel like it anymore because the day is already way too short.

This is roughly what my day looks like.
4:45 a.m. get up
5:05 a.m. head to work
6:00 a.m. work starts
3:30 p.m. work ends
4:30 p.m. home
5:15 p.m. sports
6:45–7:00 p.m. home
9:00 p.m. go to sleep

My partner’s schedule is similar, except that she has citizen consultation hours until 6:00 p.m. on Tuesdays.

@Bauexperte,

I have read about the noisy decentralized controlled residential ventilation from various internet research and the data sheets of the respective manufacturers, for example InVenter Twin at about 60 dB seems very loud to me. Especially my partner reacts very sensitively to high-pitched sounds and humming noises. The price difference of about 1500 EURO to the central controlled residential ventilation seems moderate to me in view of this.

What other recommendable German systems are there? At the moment, the topic of controlled residential ventilation is really bothering me, especially because I plan to live in it for the rest of my life (that’s the plan). And trying to retrofit something afterwards can only be a compromise and more expensive...

Regards
mirage
P.S. no, I am not a police officer