Case 2: Smoke back-drafts and contamination in a ventilation system

Case 2: Smoke back-drafts and contamination in a ventilation system

The picture corresponds to the installation of several chimneys of combustion gases in a residential building in La Rioja. Twin wall stainless steel chimneys have been installed as required by the norm UNE 123001 but, when completing the installation, the following mistakes are made:


  • The three evacuation chimneys are completed at the same height.
  • They reach the same height that the concrete element with the ventilation outlet in the annexed building.


  • Revoke problems in the chimneys, especially if the three of them are not working at the same time.
  • In the case the chimneys are not working at the same time, the smoke expelled by the working chimneys may get into the one at rest due to the stack effect produced by the last one.
  • Depending on the predominant winds in the área, the stack effect on the smoke will also take place in the annexed ventilation system as the fume outlets of the annexed chimneys have been set at the same height.

Recomendaciones e instrucciones de colocación de remates de chimeneaProper solution:

Part 6 of the norm UNE 123001 points to the different possibilities which may take place when locating a coping on the roof of a building. The norm also makes it clear that the smoke outlet must be installed, at least, 40 cm. above the ventilation air intake element.

The Technical Department at Sabanza has designed a document about the installation of chimney coping which can be downloaded at the section of downloads or just by clicking on the image.