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