Ventilation through the window rabbet or a decentralised ventilation?

It sounds compelling: Ventilation through the window rabbet is inexpensive, easy in mounting and cleaning. Without the need of special filter systems or electricity cables, simple mechanic ventilation gaps in the folding window frame enable fresh air and mould prevention user-independently.

For the ventilation via window rabbet, a part of the sealing strip is replaced by a simple ventilation gap in the frame. The air from the outside enters the room through the  lamellar-like parts at the lower rabbet space of the window and rises until it reaches the room through the space between frame and wing at the top. This fulfils the demanded user- independent ventilation according to the DIN 1946-6. However, before the implementation one should consider the following aspects.

1. There are rarely ideal situations

In order for the ventilation via window reveal to work, there has to be an airflow between two parallel building fronts facing each other. For houses with windows on only one side, or buildings with closed inner courtyards, like it is common for apartment complexes, the principle that depends on a continuous air exchange, is not a suitable option. Moreover it is to be considered that the scent from humid rooms such as kitchen or bath might be spreading throughout the rooms.

2. The energy balance worsens

For new buildings or renovation projects the energetic optimisation is of huge importance. Modern, triple-glazed windows as well as insulated facades are to keep the heat inside the building. The easy principle with the openings in the window's frame  to the contrary effect, since it does not enable any heat recovery. Especially during the winter this could lead to a continuous cooling of the rooms.

3. Valves are not individually adjustable

In case of strong wind exposure the valves of the window rabbet decrease to avoid draught and exclude rainwater. Nevertheless the gaps never close completely, so there might still be draught. Buildings that are subject to the protection against dust and pollen are not recommended to be opened with a ventilation through the window rabbet. Strictly speaking, those gaps even object the recommendations by the police regarding burglary and invading toxins, i.e. during fires or chemical accidents.

4. Humidity protection is not sufficient for inhabited houses

Suppliers of window rabbet ventilation often grant a ventilation for humidity protection with their devices. It is lesser known that those dehumidification devices only cover the protection if the inhabitants are present. If the required air exchange is not fulfilled and there is damage caused at the building, the planner faces a serious liability risk.
For a space of 70 square metres, the air volume exchange lays at about 30 cubic metres per hour. For inhabited buildings with an average use the norm recommends a so-called nominal ventilation of 95 cubic metres an hour.

Decentralised ventilation with heat recovery as an alternative?

The fulfilment of the required air exchange depends on multiple factors that have to be considered for the issuing of a ventilation concept. Next to the insulation standard, living space and number of inhabitants, for example the location and the natural air movements come into play in the decision for a suitable ventilation system.
A modern alternative to the ventilation through the window rabbet is the decentralised ventilation with heat recovery. The fresh air flows through purposefully placed ventilation devices from the outer walls to the inside living space. This may be more expensive in acquisition but more so efficient and therefore saves valuable energy.

Window rabbet ventilationDecentralised ventilation with heat recovery
Mould prevention (given ideal conditions)++++
Heat recovery-+++
Individual possibilities of adjustment-+++
Frost protection-+++
Sound protection-+++
Aquisition costs++++

ideal +++

very good ++

good + 

insufficient -

Comments (3)

  1. Gustav Sucher at Tuesday, 18. September 2018
    Mein Onkel überlegt gerade, ob er solche Fenster einbauen soll. Daher danke für diesen Blog. Nun kann ich etwas mit ihm über die Vor- und Nachteile dieser Fenster reden! Danke!
  2. Leo Gucker at Monday, 22. October 2018
    Hallo, wie sieht denn so ein Filtersystem aus? Ich habe schon oft davon gehört, dennoch noch kein solches System gesehen. Oder ist das runde Ding auf dem Bild an der grünen Wand solch ein System? Danke im Voraus.
    1. inVENTer GmbH at Monday, 22. October 2018
      Hallo Herr Gucker,

      die inVENTer-Filter unterstützen unsere dezentrale Lüftungsanlagen und filtern die Partikel aus der Luft, bevor diese in den Innenraum gelangen können. Die Filter befinden sich in der Innenblende unseres Lüftungssystems. Weitere Informationen diesbezüglich finden Sie hier:

      Mit freundlichen Grüßen,
      Ihr inVENTer-Team

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