An important point for improving the air tightness of air ducting systems is the use of ducts with factory-fitted air-tight connections with flat gaskets [1]. Furthermore, to install tight air ducts, not only the installation itself is crucial, but also upstream processes and participants in planning (e.g. selection of the right standard), manufacturing (e.g. selection of sheet thicknesses) and transport (e.g. load securing and fixing of components) play a significant role.

In order to comply with the required European standards, care must generally be taken when handling the air duct parts.

The air duct parts:

  • must be transported conscientiously and stored cleanly.
  • must not be pushed over the connecting flange.
  • must be visually inspected for damage before starting installation.
  • no usage when damaged.

The following instructions must be observed during installation:

  • Depending on the air tightness class requirement, apply the duct sealing tape crosswise in the corner area and to the inner edge of the connecting profile. The tape may only be used once, i.e. after dismantling the air duct parts, the sealing tape must be replaced in order to reuse these parts.
  • The profile flanges must be screwed to the corner screw connections and checked again for strength after approx. 48 hours.
  • From an edge length of > 500mm (depending on the air tightness class and operating pressure), threaded clamps or sliding strips (min. 100mm long) must be fitted evenly over the edge length of the flange. The use must be adapted to the respective conditions and tested.
  • Symmetrical suspension of the ductwork must be maintained to ensure air tightness.
  • Fitting parts are delivered with loose frames (depending on the air tightness class provisionally with sheet metal friction bolts (tightness class A) or loose (class B, C, D)). After shortening the component, the frame must be fitted and then fastened and sealed. Fixing and sealing must be carried out in accordance with the requirements of the construction site or design specifications (pressure rating, tightness class).
  • A tightness test cannot be passed in case of defective execution of the mounting.
  • The installation has an influence on the tightness of the duct system of far more than 50%.
  • The final air tightness of the duct system is in the hands and therefore the responsibility of the installation company [2].


[1] Leprince V., Hurel N. and Kapsalaki M.,2020. VIP 40 Ductwork airtightness – A review.  AIVC, April 2020

[2] Installation instructions for ductwork. 2015


Posted in: Ductwork airtightness