Choosing industrial extractor fans by headline rating alone can leave a Swansea kitchen, workshop or toilet damp, hot or odorous. Calculate airflow and account for duct resistance. Then match the fan, controls, IP rating and electrical installation to the space.
Size airflow before choosing a fan
Required airflow is room volume in m³ × target ACH. This gives a starting result in m³/h. A 100 m³ workshop needing 8 ACH needs around 800 m³/h before duct losses. Toilets often need 6–10 ACH. Stores need 3–6 ACH, while workshops need 6–12 ACH.
Work out room volume first
Measure length, width and ceiling height in metres. Then multiply them. A 10 m by 5 m unit with a 3 m ceiling has a volume of 150 m³. At 8 ACH, its starting extract target is 1,200 m³/h.
Practical sizing rule: Calculate the m³/h target first. Then ask for the fan’s duty point at your expected duct resistance. The catalogue’s free-air figure describes performance with no ductwork attached.
Add capacity for duct resistance
Ducts, bends, filters, grilles and backdraught shutters create static pressure. This reduces the airflow that actually reaches the room. Check the manufacturer’s fan curve before choosing. It shows airflow at the expected pressure, not just fan diameter or free-air rating.
Compare more than the advertised extractor fan capacity. Record the free-air and duty-point m³/h figures. Also record impeller diameter, motor input in kW, voltage, phase and full-load current. Check the IP rating and sound pressure level at the stated measurement distance.
A 230 V single-phase fan may suit a small unit. A larger three-phase model can suit higher duties. The electrical supply must support that choice.
The airflow calculation sets the required duty. Wattage and fan diameter alone do not prove performance. Two similar fans can give very different airflow under static pressure.
Choose the fan and route as one system
Axial fans suit short, straight wall runs. Centrifugal, inline and roof fans usually suit longer ducts or higher resistance.
| Fan type | Best duct route | Pressure handling | Typical use |
|---|
| Axial | Short, straight wall exit | Low | Toilets and simple stores |
| Inline mixed-flow | Moderate duct length | Medium | Offices and utility areas |
| Centrifugal | Longer runs with bends | High | Workshops and plant areas |
| Roof extract | Vertical roof discharge | Medium to high | Larger commercial premises |
Match the fan to the duct run
An axial fan can suit a short wall opening. It often struggles with long runs and elbows. Centrifugal or inline fans cost more at first, but they can keep the designed airflow through more resistant ductwork.
Plan noise and discharge points
Noise comes from the motor, air speed and vibration. Check sound data, mounting and discharge location. This matters near workstations and neighbouring homes.
From room measurement to a usable extraction specification
1. Measure
Length × width × height
2. Set ACH
Match activity and moisture
3. Check losses
Ducts, bends, grilles
4. Specify safely
IP, isolator, controls
Provide replacement air
Extraction needs replacement air. A sealed room can make the fan pull against a vacuum. It may also create combustion risks around gas appliances.
Mounting affects both performance and installation cost. A wall or panel-mounted axial fan is often simplest. This works where air can leave through an external wall.
A window-mounted unit only suits safe glazing and weather sealing. It must also suit the site’s security needs. Ceiling-mounted and inline units can keep equipment away from occupied areas. They need supported ducts and accessible service points.
Roof-mounted extract fans suit vertical discharge. The roof opening needs correct weathering. Safe access must also be available.
Fit an external grille or louvre where appropriate. Check that a backdraught shutter does not add excessive resistance.
Moisture, heat, grease, dust and fumes need different extraction approaches.
Commercial kitchen extraction needs canopy capture and grease filters. It also needs cleanable ducts, fire safety and replacement air. The discharge point must suit the cooking load.
A failed fan may not be a like-for-like replacement. Cooking output, duct condition or system size may have changed.
Workshops need source capture
Dust and fumes need capture close to where they form. HSE COSHH guidance requires control of harmful substances. Welding, grinding or solvent work may need an LEV specialist. General room extraction may not be enough.
The most common mistake is relying on a room fan for a local hazard. A fan across the room cannot catch fumes at the bench.
Damp rooms need suitable protection
Damp rooms may need humidity controls and run-on timers. The IP rating must suit the exact location. Suitable circuit protection, isolators and electrical testing should form part of the installation.
Sector needs should refine the first ACH figure. In a warehouse, ventilation may need to address vehicle exhaust or heat build-up. Poor airflow in racking aisles can also be a problem.
A production area may need separate zones for process heat. It may also need zones for packaging odours or machine emissions. Public toilets often suit low-speed continuous extract. Humidity and occupancy controls can also use timed overrun.
Kitchen and workshop systems should capture pollutants near their source. Replacement air must reach the extracted area. Otherwise, the calculated airflow may not occur during normal use.
Avoid the costly installation mistakes
A correctly sized fan can still fail when its duct, power supply, controls or maintenance access are wrong.
Check power, IP and isolation
Larger fans may need a dedicated circuit or three-phase supply. Confirm cable size, protective device, motor wiring and local isolator before ordering. Keep test paperwork for future EICR records.
Dirty filters, grease and blocked grilles reduce airflow. Plan safe access for cleaning, shutters and roof equipment. Sensors should detect the true room condition. They should not react to a cold draught.
This advice is not enough for hazardous dust or flammable vapours. It is also not enough for welding fumes, spray booths, laboratories or high-grease commercial kitchens. These settings may need specialist LEV, filtration and fire-rated ductwork. They may also need commissioning and a compliance assessment. Potentially explosive atmospheres may need ATEX-rated equipment designed to BS EN 14986. A standard extractor fan is not suitable.
Before buying, ask a qualified Swansea electrician or ventilation contractor to check the airflow and fan curve. They should also check the duct route, IP rating, circuit and isolator location.
Your questions answered
What fan size does my space need?
Multiply room volume by target ACH. Choose a unit that gives that m³/h at the duct system’s pressure.
Should I choose axial or centrifugal?
Choose axial for a short, direct route. Choose centrifugal or inline for longer ducts, bends, filters or higher pressure.
How much airflow does a workshop need?
A general workshop often needs 6–12 ACH. Dust, welding fumes and solvents need source capture under COSHH.
Can one fan serve a commercial kitchen?
One fan can form part of the system. The canopy, grease control, duct cleaning, discharge and replacement air must suit cooking load.
The IP rating depends on the wet or dusty location. Check splash risk and the manufacturer instructions.
Long ducts and bends can reduce airflow. Blocked grilles, closed air paths and dirty filters also reduce actual airflow.
Specify the airflow before buying
Start with room volume and ACH. Then select a fan that gives the required airflow at real duct resistance. Match noise, controls and electrical protection to the site.
Seek specialist ventilation advice for fumes, explosive dust or grease-heavy cooking.
