What is a Back Draught Shutter?

A back draught shutter (also spelled back draft shutter) is a mechanical device installed within ventilation ducting to prevent reverse airflow—stopping cold or contaminated air from re-entering a room when the fan is inactive. It is particularly critical in UK residential and retrofit projects to maintain thermal comfort and comply with Part F (Ventilation) of the Building Regulations (2021 edition).

Types & Mechanisms

  1. Integral Shutters:
    • Built into extractor fans (e.g., bathroom/kitchen fans).
    • Typically use a lightweight hinged flap or membrane that opens under fan pressure but closes via gravity when off.
  2. Standalone Shutters:
    • Fitted separately in duct runs, often for centrifugal fans or complex systems.
    • May use thermo-electric actuators for precision (e.g., in mechanical ventilation with heat recovery/MVHR systems).

Regulatory Context

  • Approved Document F (2021): Requires ventilation systems to minimise uncontrolled air leakage (Section 2.16). Back draught shutters help meet dwellings’ airtightness targets under Part L (Conservation of Fuel and Power).
  • BS EN 13141-1:2019: Covers performance testing for ventilation components, including shutters.

Practical Applications

  • Retrofit Projects: Essential when upgrading older properties to prevent cold draughts via existing ducts.
  • Extensions: Ensures new ventilation systems (e.g., kitchen extractors) do not compromise thermal efficiency.

Related Terms

  1. Centrifugal Fan: A high-pressure fan type often paired with standalone shutters for longer duct runs.
  2. MVHR (Mechanical Ventilation with Heat Recovery): Systems where shutters prevent heat loss during off-cycles.
  3. Airtightness (Part L): Shutters contribute to reducing unintended airflow in sealed homes.
  4. Intermittent Extract Ventilation (IEV): A Part F-compliant strategy using shutters for humidity control.
  5. Ductwork Leakage Testing: Shutters must be inspected during post-installation tests per BS EN 12237.