Inline Duct Fans Explained: How to Choose the Right Size for Kitchens, Offices and Small Workshops
November 09, 2026
Not every room can have an exhaust fan on an outside wall. Basement offices, interior washrooms, server and electrical rooms, commercial kitchens, grow rooms and small workshops often need air to travel through ducting before it leaves the building. This is the job of the inline duct fan — a compact fan that sits inside the duct run and pushes or pulls air through it.
What is a mixed-flow inline fan?
Inline fans come in axial, centrifugal and mixed-flow designs. A mixed-flow impeller combines the high air volume of an axial fan with much of the pressure capability of a centrifugal fan. That makes it well suited to ducts with bends, filters, grilles and longer runs, where a simple axial fan would lose most of its airflow.
The four numbers that matter
1. Air volume (m³/h)
This is how much air the fan moves. A common approach is to multiply the room volume by the number of air changes per hour the space needs — washrooms and kitchens need more air changes than offices.
2. Static pressure (Pa)
Every metre of duct, every bend, filter and grille adds resistance. A fan's rated airflow falls as resistance rises, so always check the fan can still deliver enough air at the pressure your duct system creates. Longer or more complex duct runs need a fan with higher static pressure.
3. Duct diameter
Match the fan to the duct size. Undersized ducts raise air speed, noise and resistance; oversized fans on small ducts waste their capacity.
4. Noise level (dB)
For offices, bedrooms, clinics and meeting rooms, choose a fan with a low sound rating and use the low-speed setting where possible.
Sizing examples across a typical range
The Ayzair inline mixed-flow duct fan range shows how capacity scales with duct size:
| Model | Duct | Air volume (high/low) | Static pressure (high) | Power (high) | Sound (high) | Applicable area |
|---|---|---|---|---|---|---|
| AYZAIR-100 | Ø100/125 mm | 200 / 150 m³/h | 180 Pa | 28 W | 30 dB | 8–16 m² |
| AYZAIR-200 | Ø200 mm | 850 / 700 m³/h | 350 Pa | 70 W | 50 dB | 34–76 m² |
| AYZAIR-315 | Ø315 mm | 2,300 / 1,800 m³/h | 700 Pa | 320 W | 66 dB | 60–120 m² |
All figures are nominal at standard test conditions; actual output depends on duct resistance and installation.
Where inline fans work best
- Interior washrooms and toilets with no outside wall — small Ø100–Ø150 fans running quietly.
- Offices, conference rooms and basements needing fresh-air supply or exhaust.
- Commercial kitchens and pantries — larger diameters with higher pressure to overcome hoods and filters.
- Electrical, UPS and server rooms to remove equipment heat.
- Small workshops, labs and grow rooms that need controlled airflow.
Installation tips
- Keep duct runs as short and straight as possible; use smooth bends instead of sharp elbows.
- Mount the fan on vibration isolators or a firm bracket to reduce noise.
- Choose a housing with tool-free access so the impeller can be cleaned easily.
- Double-insulated bodies add electrical safety in damp areas.
Ayzair, a Pune-based manufacturer of ventilation and cooling equipment, offers inline mixed-flow fans from Ø100 to Ø315 mm with ceiling in-line, L-bracket and wall mounting. For help choosing a size, contact the team at ayzair.com/contact.
