ᐅ Decentralized ventilation units for larger rooms (older buildings)
Created on: 1 Oct 2025 17:46
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RealUnreal
Hello everyone,
I have an older building, built in 1976.
Next year, I plan to install triple-glazed windows in several rooms.
The exterior walls have U-values mostly around 0.90, with some individual exterior walls as high as 1.4.
In one room (laundry room), I have been using a Bavarian-style ventilator (ventilation with heat recovery) for about two years, and since then, I have had no moisture problems, even though the window is always closed and sometimes a clothes dryer is running and damp laundry is being dried.
The rooms where the windows will be replaced are quite large.
One room is 66 m² (room volume 178.2 m³ (6291 ft³)).
The other room consists of a main area (living room) with 48 m² (room volume 130.39 m³ (4603 ft³)) and an adjoining kitchen (separated only by a glass door) with about 15 m² (room volume 40.96 m³ (1445 ft³)).
I would like a decentralized ventilation system with heat recovery for both rooms to avoid condensation issues with the new windows and to remove any excess humidity.
This would only replace manual ventilation since I do not want to have to ventilate constantly.
Only my wife and I live in the apartment (2 persons).
I do not want a alternating system but rather a unit with heat recovery and separate fans for supply and exhaust air.
I want to install the units myself (I also installed the Bavarian ventilator).
So, the installation should not be more complicated than the Bavarian ventilator.
The problem is that the house is built on a slope.
I can only exhaust to the front side (valley side), which has fairly large window fronts.
No more than one ventilation unit fits per room, and only if I reduce the size of one window.
In the meantime, I spoke with the company Meltem, and they said that a "heat recovery-II" unit would be sufficient for the living room.
They would recommend an airflow rate of 50 m³/h (about 30 CFM).
For the other room, they actually recommend two units with the same settings.
With the Bavarian ventilator, you generally estimate an air exchange rate of about 0.2 times per hour, so in 5 hours a complete exchange of air occurs.
I can easily achieve this or do it faster with the Meltem device.
The older "heat recovery" model (without II) is about 400.00 Euros cheaper, but the newer device is clearly recommended.
I would go for a version with a humidity sensor and controls.
What do you think?
Two units in one room is a bit difficult.
Maybe additionally window frame ventilators?
Best regards,
Unreal
I have an older building, built in 1976.
Next year, I plan to install triple-glazed windows in several rooms.
The exterior walls have U-values mostly around 0.90, with some individual exterior walls as high as 1.4.
In one room (laundry room), I have been using a Bavarian-style ventilator (ventilation with heat recovery) for about two years, and since then, I have had no moisture problems, even though the window is always closed and sometimes a clothes dryer is running and damp laundry is being dried.
The rooms where the windows will be replaced are quite large.
One room is 66 m² (room volume 178.2 m³ (6291 ft³)).
The other room consists of a main area (living room) with 48 m² (room volume 130.39 m³ (4603 ft³)) and an adjoining kitchen (separated only by a glass door) with about 15 m² (room volume 40.96 m³ (1445 ft³)).
I would like a decentralized ventilation system with heat recovery for both rooms to avoid condensation issues with the new windows and to remove any excess humidity.
This would only replace manual ventilation since I do not want to have to ventilate constantly.
Only my wife and I live in the apartment (2 persons).
I do not want a alternating system but rather a unit with heat recovery and separate fans for supply and exhaust air.
I want to install the units myself (I also installed the Bavarian ventilator).
So, the installation should not be more complicated than the Bavarian ventilator.
The problem is that the house is built on a slope.
I can only exhaust to the front side (valley side), which has fairly large window fronts.
No more than one ventilation unit fits per room, and only if I reduce the size of one window.
In the meantime, I spoke with the company Meltem, and they said that a "heat recovery-II" unit would be sufficient for the living room.
They would recommend an airflow rate of 50 m³/h (about 30 CFM).
For the other room, they actually recommend two units with the same settings.
With the Bavarian ventilator, you generally estimate an air exchange rate of about 0.2 times per hour, so in 5 hours a complete exchange of air occurs.
I can easily achieve this or do it faster with the Meltem device.
The older "heat recovery" model (without II) is about 400.00 Euros cheaper, but the newer device is clearly recommended.
I would go for a version with a humidity sensor and controls.
What do you think?
Two units in one room is a bit difficult.
Maybe additionally window frame ventilators?
Best regards,
Unreal
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RealUnreal3 Oct 2025 10:41[MEDIA=youtube]Cv0s6TgwbJg[/MEDIA]
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nordanney3 Oct 2025 11:40RealUnreal schrieb:
Let's take the "Meltem M heat recovery II" as an example. It has a capacity of 10-100 m³ per hour. At 50 m³ per hour, it produces indoor noise of 33.9 dB.
Are there any through-wall fans that can compete with that? It's like an airplane.
With my through-wall fans for basic ventilation, I have around 12 dB. At 50 m³ per hour, just over 20 dB.
The Meltem is really loud.
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RealUnreal5 Oct 2025 21:18Something different: In the area highlighted in yellow, I have a suspended ceiling grid that basically allows me to access every room from above the ceiling.
Right now, I'm focusing on the ventilation for the living room and the "swimming pool" because new windows are supposed to be installed there first.
The swimming pool was never realized and is now a normal room (extension).
In the room "Storage1," I could reach the outside and also install a central unit there.
Would that be an alternative?
How much does something like that cost compared to decentralized options?
Right now, I'm focusing on the ventilation for the living room and the "swimming pool" because new windows are supposed to be installed there first.
The swimming pool was never realized and is now a normal room (extension).
In the room "Storage1," I could reach the outside and also install a central unit there.
Would that be an alternative?
How much does something like that cost compared to decentralized options?
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nordanney5 Oct 2025 21:53RealUnreal schrieb:
Would this be an alternative? Only if you can install the appropriate ducts in both rooms. Supply and exhaust air are applied at different points on the ceiling when done correctly.
RealUnreal schrieb:
How much does this cost compared to decentralized options? Many times more. Depending on the equipment, maybe around 5 times as much (?). Much cheaper if you do it yourself.
And the question is how and where supply and exhaust air can be positioned in the rooms. It might even be a factor of 10 if it gets especially complex.
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RealUnreal6 Oct 2025 07:16nordanney schrieb:
Only if you can install the appropriate ducts in both rooms. Supply and exhaust air are applied at different points on the ceiling when done correctly.Does the position of the supply and exhaust air have to comply with specific regulations?
I would say this: In principle, it should be possible for me since the ceiling is dropped everywhere (suspended ceiling). It’s a bit tight in places, but if flexible ducts can generally be used and the openings to the rooms don’t need to be very large in diameter, it should work.
Technically, it’s basically like the installation of a decentralized unit, right? Except there’s a distribution box in between that distributes the air to the rooms. So, you would only need one central location for the main unit and from there to the distributor, then into the individual rooms?
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RealUnreal6 Oct 2025 08:03nordanney schrieb:
Now just a few filler words…I don’t understand this 🙄
Is it possible to install a device like this yourself if you are able to install a decentralized unit?
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