When it comes to supplying large volumes of air in compact systems, the double inlet fan (also known as a double inlet centrifugal fan, double inlet blower or double-suction fan) is a highly efficient solution. This type of fan is commonly found in HVAC units, air handling systems, and industrial ventilation equipment - but what makes it different from a standard centrifugal fan?
What Does "Double Inlet" Mean?
A double inlet fan features a centrifugal impeller that draws air in from both sides of the fan wheel, unlike a single inlet fan that only draws air in from one side. Air enters from two inlets, travels through the impeller blades, and is discharged radially outward into the fan's scroll housing.
How Does a Double Inlet Fan Work?
Air intake: air is sucked in from both sides of the impeller (twin-suction)
Impeller rotation: generates centrifugal force
Air discharge: exits the housing in a single direction with increased pressure
Because the airflow is balanced on both sides of the rotating wheel, the double inlet centrifugal fan offers higher airflow capacity while maintaining stable pressure, and helps minimize axial load on the motor shaft.
Advantages of Double Inlet Fans
| Advantage | Description |
|---|---|
| ✅ Higher airflow | Pulls air from both sides to deliver more volume |
| ✅ Compact for large air volume | Ideal for limited installation space in AHUs and FCUs |
| ✅ Balanced shaft loading | Reduces bearing stress and increases fan lifespan |
| ✅ Suitable for low-medium pressure | Perfect for HVAC supply and return air systems |
Common Types
Double inlet fans are typically forward curved centrifugal fans centrifugal fans due to their high-volume performance, but double-inlet backward curved centrifugal fans are also used when higher efficiency or pressure is required.
Our product range includes:
Forward centrifugal fans-often used as double inlet blowers in FCUs
Backward centrifugal fans and backward curved centrifugal fans – available for higher pressure versions
Intelligent upgrades using 400mm EC backward curved centrifugal fan or EC axial fan for greater efficiency
Typical Applications
| Application | Recommended Fan Type |
|---|---|
| Fan Coil Units (FCU) | Double inlet forward centrifugal fan |
| Air Handling Units (AHU) | Double inlet backward centrifugal fan |
| HVAC Supply / Return Air Box | Double inlet blower with EC motor (energy saving) |
| Air Curtain, Cabinet Ventilation | Compact double inlet squirrel cage fan |
| Industrial Process Ventilation | 355mm backward centrifugal fan (high pressure version) |
Double Inlet vs Single Inlet Fan
| Feature | Double Inlet Fan | Single Inlet Fan |
|---|---|---|
| Air Intake | Two sides | One side |
| Airflow Volume | Higher (larger capacity) | Lower |
| Space Efficiency | More air in compact build | Requires larger size to match airflow |
| Usage | HVAC, FCU, AHU, blowers | Ducted ventilation, exhaust |
| Example Product | Double inlet forward centrifugal fan | 400mm EC backward curved centrifugal fan |
Conclusion
A double inlet fan is a centrifugal blower that draws air from both sides of its impeller to produce greater airflow in a compact footprint. It is particularly well-suited for fan coil units, air handling units, HVAC supply systems, and environments where space is limited but performance requirements are high.
Whether you need a double inlet forward centrifugal fan for large airflow in a FCU or a double inlet backward curved centrifugal fan for higher pressure HVAC applications, we provide a full range of solutions - including 355mm backward centrifugal fans, 400mm EC backward curved centrifugal fans, and EC axial fan options for energy-efficient upgrades.
