When choosing the right fan for HVAC or industrial ventilation equipment, many users wonder - is a plug fan a centrifugal fan? At first glance, plug fans and centrifugal fans seem quite similar, but their construction and air delivery methods reveal some important differences.
In this article, we'll explain how plug fans are related to centrifugal fans, what makes their design unique, and when to select each type for your system. Examples are included using our key products such as forward centrifugal fans, 355mm backward centrifugal fans, and 400mm EC backward curved centrifugal fans.
What Is a Plug Fan?
A plug fan (also known as a plenum fan) is technically a type of centrifugal fan, but with one major structural difference - it does not use a spiral scroll housing.
Plug fans feature a backward curved centrifugal impeller, typically mounted inside the cabinet of an air handling unit (AHU) or plenum box. The air is discharged freely in all directions into the plenum instead of being channeled into a duct via a volute casing.
Plug Fan Features:
Backward curved impeller
No scroll / volute casing
Air discharges into a plenum chamber
Easy for cleaning & filter access
Often paired with EC motors for energy efficiency
What Is a Centrifugal Fan?
A centrifugal fan also uses a spinning impeller to move air, but it includes a scroll-shaped housing (volute) that directs the air out into a defined outlet.
Types include:
Forward centrifugal fan – high volume, low pressure
Backward centrifugal fan and backward curved centrifugal fan – high efficiency and pressure
Radial blade fan – heavy duty, dirty air handling
Our products like the 355mm backward centrifugal fan and 400mm EC backward curved centrifugal fan are examples of high-pressure centrifugal fans designed for ducted ventilation systems.
Plug Fan vs Centrifugal Fan – What's the Difference?
| Item | Plug Fan | Standard Centrifugal Fan |
|---|---|---|
| Scroll Housing | ❌ No | ✅ Yes (volute or spiral casing) |
| Impeller Type | Backward curved | Forward or backward curved |
| Air Discharge | Free into plenum (multi-direction) | One defined outlet direction |
| Static Pressure Capability | Medium | Medium-high (especially backward curved type) |
| Typical Motor | Often EC motors | AC or EC motors |
| Space Requirement | Compact in AHU | Requires space for housing and duct connection |
Is a Plug Fan a Centrifugal Fan?
Yes - plug fans belong to the centrifugal fan family, specifically backward curved centrifugal fans, but without the scroll housing.
This unique structural change gives them greater flexibility in air handling units, filtration cabinets, and modular HVAC systems, where multi-directional airflow in a compact space is needed.
When Should You Use a Plug Fan?
Choose a plug fan if:
- You are installing into a plenum or AHU casing
- Space is limited and easy cleaning access is important
- Noise and energy savings are priorities (use EC plug fan)
- Choose a standard centrifugal fan (such as a forward centrifugal fan or backward curved centrifugal fan) if:
- You need high static pressure to drive air through long duct systems
- You require a defined air outlet direction
- You are designing industrial ventilation or extraction systems
Role of EC Technology
Both plug fans and centrifugal fans can be upgraded with EC motors for better performance.
For example, you can specify:
- 250mm EC axial fan modules inside compact AHUs
- 355mm backward centrifugal fan with EC motor for medium pressure
- 400mm EC backward curved centrifugal fan for high-pressure air handling units
With built-in 0–10 V or PWM speed control, EC technology delivers up to 50% energy savings and lower noise versus traditional AC-motor fans.
Typical Applications
| Plug Fans | Centrifugal Fans |
|---|---|
| Small & rooftop AHUs | Ducted HVAC systems |
| Cleanroom and lab plenums | Industrial ventilation & extraction |
| Air purifiers / filtration boxes | Kitchen exhaust, dust collectors |
| Modular air conditioners | General building supply & return air systems |
Conclusion
So, is a plug fan a centrifugal fan?
Absolutely - it's a special type of backward curved centrifugal fan, redesigned without the outer scroll casing. This allows it to discharge freely into a plenum space, making it perfect for compact air handling and filtration systems.
Whether you require an EC plug fan for smart AHUs or a traditional backward centrifugal fan for ducted ventilation, we offer a full range of products - including forward centrifugal fans, 355mm backward centrifugal fans, 400mm EC backward curved centrifugal fans, and EC axial fans - to meet your application needs.
Want help choosing the right fan type?
Contact us now for solutions tailored to your airflow, pressure, and installation requirements.
