FAQs regarding natural smoke and heat ventilation – Airflow performances of natural ventilators

Preamble: Information given by EUROLUX in that note are checked by IFI and CSTB, which are the two notified laboratories which prepared the testing procedure presented in EN 12101-2, Annex B.


Natural Smoke and Heat Ventilators (NSHEVs) are in some cases offered by several manufacturers with high airflow performance for installation on flat roofs and with much less technical equipment than most products, e. g.:

  • they shall perform well without wind deflectors,
  • they have only one flap with a low opening angle,
  • the airflow efficiency claimed is 0.60 and above.

NSHEVs types concerned :

  • Double flap ventilators with and without upstand
  • One flap ventilators, roof mounted opening angle less than 120°


  • In some cases, manufacturers even present CE certificates for such types of NSHEVs.
  • This document mostly is not concerned with NSHEVs installed on sloped roof (30° and more) or wall mounted.


What is the highest reasonable level of airflow performance which can be expected for these types of ventilators?
  • Double flaps NSHVs with upstand 300mm high minimum and without wind deflectors:

    • c v is declared between 0.35 and 0.45 mostly.

  • Double flaps NSHEVs without upstand (often installed on glass roofs) and without wind deflectors:

    • c v is declared between 0.15 and 0.35 mostly.

  • One flap ventilator, with or without upstand, angle of opening less than 120°:

    • c v can be less than 0 (negative).
What are the risks in case of installation of such types of ventilators?
  • Double flap ventilator:

    • The efficiency for smoke evacuation of the building is reduced with the same ratio that the difference between announced performance an actual.

  • Double flaps NSHVs with upstand 300mm high minimum and without wind deflectors:

    • As an example for a claimed performance of c v = 0.65 instead of 0.40: The outflow of smoke is reduced by almost 40%.

  • Double flaps NSHEVs without upstand and without wind deflectors:

    • As an example for an announced performance of c v = 0.65 instead of 0.25: The smoke outflow is reduced by almost 70%.

  • Therefore the efficiency of such a system can be vastly reduced.

  • One flap ventilator, with or without upstand, angle of opening less than 120°:

    • In that case the coefficient of efficiency even can be negative. This means that there is the possibility, in case of windy conditions, for the outside wind to blow the smoke towards the floor and to increase considerably the risks due to the smoke. Using of NSHEV never should be done without considering the wind. Where the wind influence is not sufficiently covered by the products themselves, by mounting or by other systems (e.g. wind sensitive control systems) the NSHEV are not only inefficient. They are also dangerous and increase the risk for the user, the risk for the fire fighters and the risk for the real property.
What are the reasons explaining that wrong performance information?
  1. Fraud: Manufacturer uses test reports limited to wall mounting of NSHEVs also for installation on roofs.

  2. Manufacturer uses reports of tests done prior to harmonization of test procedures as defined in the EN standard:

    • Which did underestimate the effect of side wind,

    • Some CE certificates in early days of implementation of the EN standard did not specify in detail the limits for the product use. Many of these certificates have been updated. But it is possible that commercial departments of manufacturers still distribute the “older versions”, more favorable.

  3. With the introduction of the EN standard, numerous new bodies without prior experience in smoke ventilation were notified. Which led to errors in the certificates issued by some of these notified bodies, for example certificates including possibility of installation on flat roofs, when the ventilators were only tested without side wind effect.
What to do in case of uncertainty?
  • Clients should refuse such types of products.

  • Please ask for handing out not only for certificates but for the test reports to check the conditions of test, side wind effect and wind deflectors for example.

  • When help is needed, send information to your national manufacturer association as a member of EUROLUX for explanations (see http://www.eurolux-sv.de/eng/members.html). It will check with the laboratories in charge.
zurück zur FAQ-Übersicht