Passive stack ventilation

Description
Vents (usually located in kitchens and bathrooms) connected by near-vertical insulated ducts to ridge or tile terminals on the roof. Warm, moist air is drawn up the ducts via a combination of the stack effect and wind effect.

Unit cost of installation (3 bed semi)
From £1,300 dependant on ease of installation of ductwork.

Bulk cost of installation
Data not available

Maintenance
Periodic cleaning may be needed particularly in kitchens.

Lifetime
Should last the life of the dwelling.

Technical suitability
Capable of controlling relative humidity below 70% (the critical level). Can be used in conjunction with other forms of ventilation such as extract fans. Humidity-sensitive inlets are available to restrict flow of air when humidity is low, thus reducing heat loss when ventilation is not needed. No electrical connection is needed so there are no running costs associated with system.

When ducts pass through an unheated space such as a loft the ducts should be insulated. Bends in the ductwork should be no greater than 30o to the vertical so as not to restrict the air flow.

Non-technical constraints
Silent in operation, and well received by occupants - they are therefore unlikely to be tampered with.

Installation as a retrofit measure may be difficult depending on layout of the dwelling.

Potential concerns with fuel poor
No specific issues.

Ancillary benefits

Trigger points for work
Major refurbishment, Random remediation.

Technical Guidance Available
» BRE Information Paper IP13/94 'Passive stack ventilation in dwellings' 1994