NBS Source
Passive Vapour Vent MK2


The Passive Vapour Vent MK2 contains a permeable membrane within the main plastic circular tube. This encourages moisture migration due the differences between external and internal temperature and air pressure.

The membrane acts as a molecular sieve, allowing water vapour to pass to the outside whilst resisting rapid air movement and therefore heat loss. The vent is also fitted with a specially designed cowl which counteracts the detrimental effects of external wind on performance.


  • No moving parts.
  • Works passively 24 hours a day (a passive dehumidifier).
  • Quiet operation (generates no noise).
  • Low installation cost.
  • Available in standard, extendable or high rise version.


  • Reduces draughty air flow and heat loss.
  • Suitable for most wall thicknesses.
  • Works at peak condensation times.
  • No night time disturbances from compressors or fans.

General information


Pr_70_65_04_28 External wall grillesPrimary


U90/340 Through wall ventilator ducts

U90/340 Through wall ventilator ducts

Specification data - External wall grilles

Product Reference

Passive Vapour Vent MK2




High Rise

Fitted with special integral rubber seal and compact cowl which alleviates the need for exterior access and allows installation from the interior.

Tube diameter

102 mm

152 mm

Tube length

350 mm

350 - 600 mm

Extendable only.

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Passive Vapour Vents