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TECHNICAL SELECTION GUIDE
How to Select Axial, Centrifugal, Inline and Roof Fans
Fan type is not selected from airflow alone. System pressure, duct arrangement, mounting location, conveyed air, temperature, noise, efficiency and maintenance access determine whether an axial, centrifugal, inline or roof fan is suitable.
Direct answer
Fan type is not selected from airflow alone. System pressure, duct arrangement, mounting location, conveyed air, temperature, noise, efficiency and maintenance access determine whether an axial, centrifugal, inline or roof fan is suitable.
Technical review: MDES Engineering Technical TeamUpdated: 2026-10-25
Axial fans
Axial fans move air along the fan axis and are commonly used for high airflow at low-to-medium pressure in short ducts, walls, tunnels, car parks, cooling and process ventilation. Cased, wall, jet and explosion-protected versions suit different duties.
Centrifugal fans
Centrifugal fans draw air into the impeller and discharge it radially, allowing higher system pressures. Impeller geometry and material are important in long ducts, filters, cyclones, process extraction, pneumatic conveying and dusty air.
Inline fans
Compact fans installed directly in circular or rectangular ductwork for general ventilation and local exhaust. Service access, noise, vibration isolation and duct connections must be considered.
Roof fans
Roof fans discharge exhaust air above the building. Weather protection, curb, backdraft damper, wind, access and roof waterproofing must be coordinated.
Final selection
For every type, design airflow and static/total pressure must meet on the fan curve. Motor power, efficiency, speed, temperature, density, corrosion, particles, ATEX and smoke-extract classification are checked separately.
Quick fan-type comparison
| Fan type | Strength | Typical application |
|---|---|---|
| Axial | High flow, low-medium pressure | Tunnel, car park, short duct |
| Centrifugal | Medium-high pressure | Long duct, filter, process |
| Inline | Compact in-duct mounting | General supply/extract |
| Roof | Direct roof exhaust | Building and industrial extract |
Key points
- State airflow and pressure at one operating point.
- Identify static or total pressure.
- Provide temperature, gas content and duty cycle.
- Assess noise, efficiency and service access together.
Frequently asked technical questions
Can an axial fan be used on a long duct?
Only if its curve meets the duct resistance at design airflow.
Is a centrifugal fan always stronger?
It often produces higher pressure, but correct selection depends on airflow, efficiency, impeller and system curve.
Does a roof fan need a curb?
A suitable curb, waterproofing and service detail are normally required.
What information is needed for quotation?
Provide airflow, static or total pressure, temperature, air content, duty, electrical supply, mounting, noise and certification requirements.
Technical references
- Manufacturer fan performance curves
- Project duct pressure-loss and system-curve calculations
- Applicable fire, ATEX and motor standards
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