Central ventilation systems in residential buildings: Proper planning for fail-safe operation

The topic of energy efficiency is and remains one of the top issues in the construction industry.

The reasons for this include the numerous energy requirements of the Energy Saving Ordinance (EnEV) in the area of renovations and the new construction of residential and office buildings. In particular, the building shells should accordingly be insulated to be as airtight as possible in order to retain in the building both the heat used in winter and the cooling achieved in the summer. A requirement that has a positive impact on the balance sheet but a negative impact on the exchange of air: The previous means of ‘natural’ air circulation through windows and gaps etc. is no longer used; this means used air and pollutants remain in the room. The resulting moisture also remains in the room and thus facilitates the build-up of mould.

In order to avoid this, building users must in theory ventilate their rooms approximately every two hours – which, particularly in residential units owned by working people, is simply not possible in practice. The German Building Energy Act (GEG) takes these facts into account. It specifies requirements for a minimum air exchange which is regulated by means of DIN 1946-6. In accordance with this DIN standard, a project-related ventilation concept must be created for new buildings and renovations. Architects and planners thereby assume tangible responsibility. It is their task to proactively notify the builders of directive DIN 1946-6. If they fail to do so, the principal may assert corresponding recourse claims in the event of damages. The installation of fan-controlled ventilation and extraction – either as a centralised or decentralised ventilation system – to allow the automatic control of air in the living space avoids matters ever coming to this. Particularly in the central ventilation system, there are a few matters to note in terms of the insulation.

Central ventilation systems: Planning makes all the difference

In the case of a decentralised ventilation system, built-in wall devices are inserted into either the exterior wall or directly into the masonry. As no complex piping systems have to be laid, this type of ventilation is suitable in particular for retrofitting in existing buildings and in individual living spaces.

The installation of a central ventilation system on the other hand involves much more intensive planning and is suitable for use in core renovations and new buildings. In the context of central air extraction and supply technology, a central ventilation device with an air extraction and supply fan is fitted in the cellar, for example. Pipes then run from these fans throughout the entire building. The central ventilation device thus regulates the air in multiple residential units.


In the case of central extraction technology, the air is discharged centrally and fresh air is fed in decentrally, which allows the residential units to be controlled individually. Both systems give rise to low air pressure which is offset by external wall valves. In order to design the entire ventilation system to be fail-safe in the long term, the pipes must be insulated in all cases. A further advantage: Proper insulation of the air-duct network lays the groundwork for ‘efficient heat recovery’, whereby the heat from the extracted air is transferred to the fresh air. In this regard, a distinction is to be made between the following requirements:

1. Pipes with cold air which pass through warm rooms
This situation occurs primarily in the case of external and outgoing air pipes. The problem here lies in the temperature differences: If the temperature in the pipe is lower than the external temperature, condensation, and therefore corrosion, occurs on the external surface of the pipe. The moisture on the pipe is also a breeding ground for the build-up of harmful bacteria.

To avoid condensation, the insulation must offer as high a vapour diffusion resistance factor as possible, i.e. the insulating material must not absorb water. Kaiflex insulating materials excel here with excellent values of up to μ ≥ 10,000. The insulating materials has also a positive impact on the ambient air quality.

In the case of non-insulated exterior wall feed-throughs, it is essential to ensure that the insulation is laid up to the cold areas of the exterior wall. In accordance with DIN 1946-6, the insulation layer thickness on the external air pipe through the wall must amount to at least 60 mm; for the outgoing air pipe within the building it must be at least 40 mm.

2. Pipes with warm air which pass through cold rooms
This phenomenon can be found particularly in the case of air supply and extraction pipes. Here, temperature differences may also bring about problems: Uninsulated pipes demonstrably lead to heat losses. Condensation may also form on the inner surface of the extraction pipe.

In accordance with DIN 1946-6, the insulation must offer thermal conductivity of at least λ = 0.045 W/(m·K). Kaiflex insulating materials have a value of up to λ = 0.033 W/(m·K) , and are thus ideally suited to these requirements.

The thickness of the insulation depends largely on the external temperature, such as whether the pipe runs along the roof or in the basement. Here, the ventilation standard DIN 1946-6 regulates the minimum insulation material thicknesses for air pipes laid in different environments outside of the thermal envelope (such as in an unheated basement or attic).

3. Pipes with warm air which pass through warm rooms
In this case, neither of the two problems are generally relevant. If, however, the pipe is to be protected from the plaster, which cannot be allowed to come into contact with the raw material, insulation is recommended.

4. Noise protection
It is well established that it is annoying and unpleasant for residents if circulation noise can be heard. Compliance with the noise protection standard DIN 4109 ensures that sufficient air and structure-borne sound insulation is provided. Kaimann insulating materials provide the necessary vibration insulation in this regard. Open-cell foams absorb sound waves by allowing the sound wave to enter into the material and then be cushioned by means of friction.


(1) Definition of air pipes
External air pipe: Transportation of fresh air outside of the building to the central ventilation device
Outgoing air pipe: Transportation of heat-extracted exhaust air to the outside
Supply air pipe: Transportation of the heated air from the central unit to the rooms
Extracted air pipe: Transportation of used room air to the ventilation device