What Is a Bathroom Exhaust Fan? Types and Selection Criteria
A bathroom exhaust fan is a small-diameter electric fan fitted into a ventilation duct to expel humid, stale air from bathrooms, toilets and laundry rooms.
A bathroom exhaust fan is a small-diameter electric fan that is fitted into a ventilation duct in the wall or ceiling and expels humid, stale air from bathrooms, toilets and laundry rooms. In spaces without a window or with poor ventilation, it removes steam and odours and so reduces condensation and mould.
Types of bathroom exhaust fans
| Type | Feature | Use |
|---|---|---|
| Wall / ceiling axial fan | Fitted at the duct opening or in a wall hole | Bathrooms and toilets with short ducts |
| In-line duct fan | Fitted inside the duct, in the ceiling void | Long ducts, several extract points |
| Fan with backdraft shutter | A flap that closes the return path when the fan stops | Shared shaft, wind-exposed outer wall |
| Timer or humidity-sensing fan | Runs on after the light goes off or until humidity drops | Bathrooms with a shower |
Selection criteria
- Diameter: The connection diameter of the fan must match the diameter of the existing duct or wall hole. 100, 120 and 150 mm are common diameters for bathroom fans.
- Air flow: The required air flow (m³/h) is the room volume (width × length × height) multiplied by the number of air changes per hour. Longer ducts and more bends reduce the actual air flow. Take the air flow value from the product label or the manufacturer's data sheet.
- Protection rating and mounting location: The second digit of the IP code indicates protection against water. An IP20 fan has no protection against water and must be mounted outside the splash zone of the shower and bath.
- Backdraft shutter: In flats connected to a shared ventilation shaft, a shutter stops air from the neighbouring flat flowing back.
- Control: The fan is connected to the light switch or to a separate switch. It helps if the fan keeps running after the light goes off, so humidity is cleared after a shower.
- Air inlet: Fresh air must come in to replace the extracted air; leave a gap under the door or fit a grille in the door.
Common mistakes
- Mounting an IP20 fan above the shower: The splash zone needs a product with at least IPX4 protection.
- Using a bathroom fan in the kitchen: Greasy vapour clogs the fan and the duct; a kitchen needs a range hood with a filter or a kitchen-type extractor.
- Choosing a diameter larger or smaller than the duct: A fan fitted without a reducer leaks or loses air flow.
- Blocking the air inlet: If the door seals tightly, the fan cannot draw air and becomes noisier.
- Confusing it with a panel fan: The axial cooling fans in the Fans category are for cooling electrical panels and equipment and are not suitable for bathroom ventilation.
Related standards
- IEC 60364-7-701: Electrical installations in locations containing a bath or shower; defines zones 0, 1 and 2 and the water protection required in them.
- IEC 60335-2-80: Particular safety requirements for household and similar fans.
Bathroom and toilet exhaust fans in the catalog
Welibaba lists 6 active bathroom and toilet exhaust fans; all are Bylion ASP series, white and IP20:
| Diameter | Standard type | Flat type (D) |
|---|---|---|
| 100 mm | ASP-100 `5510000004` | ASP-100D `5510000001` |
| 120 mm | ASP-120 `5510000005` | ASP-120D `5510000002` |
| 150 mm | ASP-150 `5510000006` | ASP-150D `5510000003` |
Compare the housing difference between the standard and flat types in the product images. For related needs, see the Fans and Ventilation category.
Frequently asked questions
What diameter of bathroom fan should I choose?
Choose by the diameter of the existing duct or wall hole. If the hole is 100 mm, fit a 100 mm fan; a duct of a different diameter needs a reducer.
Can a bathroom fan be mounted above the shower?
Only a fan with IP protection suitable for the splash zone (at least IPX4) can be mounted there. An IP20 fan must be mounted outside that zone.
How is the air flow of a bathroom fan calculated?
Multiply the bathroom volume by the number of air changes per hour. For example, a 2 × 2 × 2.5 m bathroom is 10 m³; multiplying this by the target number of air changes gives the required air flow.
Can a bathroom fan be used in the kitchen?
No. Greasy vapour clogs the bathroom fan and the duct; a kitchen uses a range hood with a filter.