VentilFlex® in ventilation ducts

VentilFlex® in ventilation ducts

VentilFlex in ventilation ducts - Kompozitor

Source: Innotéka

VentilFlex® composite chimney liner in ventilation systems

Ventilation ducts of existing, old and especially monument buildings are no longer suitable for their purpose function that is to provide the desired or required air conditions in facilities with different purposes. These ducts, mainly due to their structure, do not meet the requirements. In case of old buildings, they are not fit for meeting the relevant current requirements even with regular professional maintenance applied since they were not designed for that purpose.
What are the subject requirements and how are they to be met?
By these days, it has become an obvious demand to have different alternative air conditions in the various rooms of a building at the same time. The number of air-exchange, temperature, moisture content and even the pressure should all be different, not to mention the number of particles and germs concerned.
Today, it is also a requirement for the buildings to be energy-effective and therefore the doors and windows are already airtight and the walls are heat-insulated even in the older buildings. Where shall we take fresh air from and what shall we do with the used air? These questions have already been responded by several good solutions, which are implemented by air handling systems and their relevant auxiliary units.
For that very purpose, Kompozitor Kft. designed their VentilFlex® duct liner technology and system in line with the following requirements.


Concerning air ducts, the most important requirement may be air-compactness,

  • since in case of forced flow, the input energy is proportional with the cube-number of the volume flow;
  • since the possibility of frame contamination has to be prevented;
  • since the planned air conditions need to be provided in all rooms concerned.

The ventilation system implemented with VentilFlex® technology meets the requirements of air compactness class D considered as one of the best classes.
The measured results of the VentilFlex® system are demonstrated in the following graph.

VentilFlex in ventilation ducts - Kompozitor
Air compactness test results of VentilFlex®

Surface roughness

The surface roughness of the wall of the air duct has a significant impact on the flow resistance. What is more important to highlight is why the smooth internal surface is good feature.
It is because less dust deposes on the surface during the operation. The dust particles – together with the moisture in the air – form a good basis for various germs. Germs include viruses, bacteria and fungi that may cause serious diseases. One of them is Legionella bacteria causing legionella disease. Smooth inner surfaces are also easier and faster to clean even with chemicals.
The surface roughness of VentilFlex® lining tubes is 0.0005 m that is competitive with other ventilation ducts produced from any other materials.

Heat and fire-resistance

VentilFlex in ventilation ducts - Kompozitor
VentilFlex® El 30 (left) and VentilFlex® El 60


The VentilFlex® liner is made of fibre-glass reinforced, heat-convertible resin (so-called composite) material. It has two types: one is made of a composite with low-combustibility and EI 30 classification, while the other one non-combustible with EI 60 classification.

Thermal characteristics

The structure of VentilFlex® lining tubes in case of the black colour design is glass fibre impregnated with three composite layers, whereas, in case of the red colour design, the number of layers is four. Average wall thickness is 3 mm. The heat conductivity of the tube material is 0.3 W/mK; therefore it is a bad heat conductor. For comparison: the heat conductivity of steel is 50 W/mK, while that of stainless steel is 16 W/mK. This means that taking the wall thickness of the steel tubes into consideration, which is 0.8–1.0 mm, the heat insulation capacity of the VentilFlex® tubes may reach up to a hundred times more than that of steels tubes.
Therefore, any application needs less insulation material. Therefore it is not common to use any insulation at the installation.

Mechanical features

The wall thickness of VentilFlex® tubes is over three times more than that of any metal ventilation ducts and the hardness of its material is not much behind the hardness of steel. Therefore, these lining tubes are a lot more stable and do not tend to dent at all. The following photos show one of those inspections that typically present features of stability.

Chemical requirements

The material of VentilFlex® ventilation duct resists to all such materials (acids, alkali), which may damage the material of stainless steel. What may be even more important than the former features is the fact that the material of the composite tube in its cured state does not discharge any material at all. Therefore, it can also be applied at duct sections transferring fresh air. Standard test results for that are available.

VentilFlex in ventilation ducts - Kompozitor
Vent pipe (VOC) test


Further, it is also interesting to mention that VentilFlex® ventilation ducts also comply with the test where more people (15 persons) through a vent pipe are to smell a duct placed in a chamber in a method that they are not aware of what is placed in the chamber. Lots of plastic products tend to fail at that test. VentilFlex® was given positive rating.

Places of application

VentilFlex® chimney liner tubes are mainly used for lining the ducts of existing buildings. The technology is fairly simple. The flat lining tube folded into half along the length is drawn in the ducts, and then it is inflated with air and hardened with steam. The liner takes the trace of the duct it is drawn into even if it is not straight. The shape of its cross section and the dimensions may be amended without having any joints in place. The installation of the liner can always be completed in a few hours without any deconstruction at all.
In Scandinavia, first of all, in Sweden, some one and a half million metres of ventilation ducts have been equipped with VentilFlex® liners to date. Especially the so-called grease ducts of industrial kitchens can be lined in a quick and safe method with the VentilFlex® technology.
The following photos show some examples of installation, where the ventilation ducts of a condominium are lined, and then having the air directed to a specific space, and are handling device controls the heat recovery and fresh air supply of the individual apartments.

VentilFlex in ventilation ducts - Kompozitor   VentilFlex in ventilation ducts - Kompozitor
Ventilation ducts lined with VentilFlex® and the space unifying the air ducts

Environmental compliance

The major technical parameters of the VentilFlex® liner tube

  • Wall thickness: 3 mm
  • Diameter: 60–1200 mm
  • Length: 3–80 m
  • Tensile strength: 150 MPa
  • Density: 1700 kg/m3
  • Heat conductivity: 0,4 W/mK
  • Heat-expansion factor: 24·10–6


The VentilFlex® technology has had the recommendation of such organisations, which were established by building and mechanical engineering deisgners’ companies in order to facilitate the designers’ work in having the best choice of appropriate materials. They include the Swedish and Byggvarubedömningen organisations.
The guarantee we provide for the technology with VentilFlex® ventilation ducts installed by our trained professional partners is 25 years.