Inline Box Fan

Wall and window fans provide simple and cost-effective ventilation where ducted systems are impractical. They are commonly used in bathrooms, kitchens, utility rooms, and small plant areas to extract humidity, fumes, and odours directly outdoors. Installation is straightforward, involving a core-drilled wall opening or window cut-out, with accessories such as backdraft shutters and external grilles for weather protection.
In wet or humid areas, fans must have appropriate ingress protection (IP rating) to BS EN 60529. Where the fan penetrates a fire-resisting wall or ceiling, fire-stopping and sleeves must maintain the fire performance of the barrier in line with BS EN 1366 principles.

Fans should be tested in accordance with BS EN 13141-6 to confirm performance, ensuring compliance with Approved Document F (ventilation) and Approved Document L (energy efficiency). Products must also meet Ecodesign Directive/UK energy efficiency requirements.
Contractors and engineers favour wall and window fans for their fast installation, low cost, and compliance with ventilation regulations, making them suitable for residential and small commercial applications.

Fire compartmentation considerations:
When installing wall or window fans, installers must exercise caution where the fan or ductwork passes through fire-resisting walls, floors, or ceilings. Penetrating a compartment or barrier may compromise the building’s fire strategy if not properly sealed and detailed. Installers should always confirm whether the construction in question forms part of a fire compartment line, protected escape route, or other fire-resisting element. If there is any doubt, the responsible person or building owner should be consulted, and clarification sought from the project’s fire engineer, building control officer, or principal designer. Where a penetration is unavoidable, approved fire-stopping methods and materials must be used in accordance with the manufacturer’s tested details and the requirements of Approved Document B.

Both wall and window fans provide direct extract ventilation by moving stale air directly outdoors. Wall fans are mounted in external walls, while window fans are installed in glazing or window frames. Some window fans are reversible and can supply fresh air as well as extract, but wall fans are usually extract-only.

They are most commonly used in residential and light commercial settings such as bathrooms, kitchens, utility rooms, and small plant areas. In larger commercial buildings, centralised ducted systems are generally preferred over wall or window fans.

These fans do not directly reduce energy consumption, but by supporting natural ventilation they can reduce reliance on air conditioning or mechanical ventilation. This can help lower overall energy use when systems are designed and controlled effectively.

Installation must follow the manufacturer’s instructions and UK regulations. Key considerations include:

• Safe electrical connection in line with BS 7671 (IET Wiring Regulations)
• Correct IP rating (BS EN 60529) for use in bathrooms or other wet areas
• Ensuring fire compartment walls or ceilings are not compromised; if a penetration is made, it must be fire-stopped in line with Approved Document B
• Proper weatherproofing with shutters or grilles
  

Relevant standards and guidance include:

• BS EN 13141-6 – Testing of residential extract fans
• Approved Document F – Ventilation performance
• Approved Document L – Energy efficiency of building services
• BS EN 60529 – Ingress protection (IP ratings)
• Ecodesign regulations – Fan energy efficiency requirements
  For smoke control applications, only fans tested as part of a system to BS EN 12101-3 may be used. Standard wall/window fans are not suitable.
  

Commissioning should follow the manufacturer’s instructions and the project specification. For residential use, this means airflow testing to confirm compliance with Approved Document F. In larger systems, CIBSE Commissioning Codes and BSRIA guidance may also be relevant.

Contractors should collect all relevant documentation during installation, including manufacturer manuals, wiring diagrams, electrical test certificates, airflow test data, and details of fixings and sealing. This ensures the O&M manual accurately reflects the installed condition.

Fans must have a local, accessible, and lockable isolator in accordance with BS 7671. Isolators should be positioned to allow safe maintenance access without the need for ladders or unsafe reach.

No. Wall and window fans designed for domestic or comfort ventilation must never be used for smoke extract. Only fans tested and certified to BS EN 12101-3, as part of a complete smoke control system, are suitable for life-safety applications. Using uncertified products would result in non-compliance with Building Regulations and a potentially dangerous system.

Commissioning records should include measured airflow rates at extract points, damper or grille positions, electrical current readings, and confirmation of compliance with design values. These provide benchmarks for maintenance and troubleshooting.

Yes. In retrofit or larger projects, run/fault signals can be connected via volt-free contacts or relays to a building management system. Commissioning should confirm correct operation and ensure signals display accurately in the BMS.

Structural wall strength, wall thickness, and window frame integrity can limit installation options. Lightweight walls may transfer vibration and noise, so correct isolation methods and sealing should be used to avoid disturbance to occupants.

Noise can be minimised by ensuring good installation quality, using vibration isolation mounts, sealing correctly, and adjusting fan speed settings. In sensitive spaces, additional silencers or acoustic grilles may be required.

Most basic fans do not include filters. Where filters are fitted (e.g. in some supply fans), designers must account for additional resistance, and maintenance schedules must specify inspection and replacement intervals.