HOLIDAY NOTICE:
A squirrel cage fan, also called a squirrel cage blower, is a type of centrifugal fan commonly used to move air through HVAC equipment, ductwork, filters, coils, and other components that create airflow resistance.
The name comes from the shape of its cylindrical blower wheel or impeller, which resembles an exercise wheel for a hamster or squirrel. The wheel consists of multiple blades arranged around its circumference and rotates inside a housing that collects and directs the air toward the discharge.
The terms squirrel cage fan and centrifugal blower are often used interchangeably in HVAC work. Blower wheel refers specifically to the rotating impeller inside the blower assembly.
Not every centrifugal fan uses a squirrel-cage-style wheel
Centrifugal fans can also use backward-inclined, airfoil, radial, and other impeller designs, each with different performance characteristics.
"Squirrel Cage" Fan Applications
Squirrel cage and similar centrifugal blowers are used in applications where air must be moved through equipment or against system resistance.
Common examples include:
- HVAC Systems: Blower assemblies in furnaces, air handlers, rooftop units, and other equipment distribute heated or cooled air through the system.
- Industrial Processes: Centrifugal fans may provide ventilation, remove fumes or airborne material, cool equipment, or supply process air.
- Electronics Cooling: Compact centrifugal blowers can move cooling air through electronic equipment where space or airflow routing is limited.
- Drying & Dehumidification: Blowers move air through dryers, dehumidifiers, and other drying equipment.
- Air Purification Systems: Centrifugal blowers can pull or push air through filters and other air-cleaning components.
- Automotive HVAC: Blower wheels move conditioned air across the heater core or evaporator and into the passenger compartment.
The exact fan design used depends on the required airflow, static pressure, available space, noise requirements, motor characteristics, and equipment configuration.
Read more about AC Blower Motors.
How Does it Work?
A squirrel cage blower wheel (also known as multi-vane style) consists of multiple blades arranged around a cylindrical wheel. The wheel is connected to a motor either directly or through a drive system, depending on the equipment design.
When the motor rotates the blower wheel, air enters the wheel near its center or inlet. The rotating blades transfer energy to the air, pushing it outward toward the wheel's perimeter.
The surrounding housing then collects and directs the air toward the fan discharge. In a typical centrifugal arrangement, air enters generally along the axis of the wheel and leaves the impeller in a direction generally perpendicular to that axis.
A centrifugal blower can move air through ductwork, coils, filters, heat exchangers, and other system components, but its performance depends on the wheel geometry, housing design, rotational speed, motor or drive configuration, and resistance of the connected system.
Is a Squirrel Cage Fan the Same as a Centrifugal Fan?
A squirrel cage fan is a type of centrifugal fan, but the terms are not exact synonyms.
A squirrel cage blower operates on the centrifugal fan principle, but “centrifugal fan” describes a broader family of fan designs; so, it's correct to say that a Squirrel Cage fan is part of the Centrifugal Fan umbrella.
Below are some other centrifugal impeller types:
- Airfoil
- Backward-inclined or backward-curved
- Radial
These designs do not have identical airflow, pressure, efficiency, sound, or power characteristics. The wheel commonly associated with the term squirrel cage in HVAC equipment is typically a cylindrical wheel containing many closely spaced blades.
Because terminology can vary by equipment manufacturer and application, the OEM model and part information should take priority over an informal fan name when identifying a replacement.
Centrifugal Fans - Impeller Types
Image credit: IQS Directory
The document attached to the article (ANSI/AMCA 99-16 - Standards Handbook), has some interesting information about centrifugal fan arrangements (pg.57), inlet box positions (pg.60), and rotation and discharge (pg. 61).
Squirrel Cage Fan vs. Axial Fan
Squirrel cage blowers and axial fans both move air, but they do it differently.
| Feature | Squirrel Cage (Centrifugal Fan) | Axial Fan |
| Air entering fan | Enters along the wheel axis | Travels along the fan axis |
| Air leaving fan | Leaves the impeller generally perpendicular to the inlet axis | Continues primarily parallel to the axis |
| Typical use | Moving air through ductwork, coils, filters, cabinets, and other system resistance | Moving larger volumes of air where relatively low pressure is required |
| Common examples | Furnaces, air handlers, packaged equipment, blower assemblies | Condenser fans, ventilation fans, exhaust applications |
What Should You Check Before Replacing a Squirrel Cage Blower?
A blower wheel that looks similar to the original is not necessarily a suitable replacement.
Whenever possible, start with the equipment manufacturer, model number, serial number, and OEM part number. Depending on the equipment, additional characteristics that may need to match include:
- Blower wheel diameter
- Blower wheel width
- Shaft or bore diameter
- Wheel rotation
- Inlet orientation and configuration
- Wheel and blade geometry
- Housing dimensions
- Direct-drive or belt-drive arrangement
- Motor voltage
- Motor speed
- Motor horsepower or power rating
- Motor mounting configuration
- Fan operating point and system requirements
Matching only the blower-wheel diameter or motor horsepower is not enough to establish compatibility.
Wheel position and clearance within the housing can also affect fan performance. When a fan or blower assembly has been disassembled, manufacturer instructions should be followed for the required wheel position, inlet clearance, alignment, fasteners, and startup checks.
For replacement parts, the OEM part number and equipment model information are generally the safest starting point. If you need any direction, don't hesitate to contact Liberty's sales team.
Choosing the Correct Blower or Replacement Part
Squirrel cage blowers are simple in principle, but identifying the correct replacement can require more than just matching the wheel's appearance. The blower wheel, motor, housing, rotation, dimensions, and system operating requirements work together as an assembly.
If you are replacing a blower wheel, motor, or complete blower assembly, start with the equipment model, serial number, and OEM part number, whenever available. This reduces the risk of selecting a component that physically fits but does not provide the airflow, rotation, clearance, or operating characteristics required by the equipment.
Frequently Asked Questions
De-energize the equipment and follow applicable energy-control and lockout procedures and manufacturer service instructions. Remove only accessible debris without bending blades or disturbing balance weights, wiring, or wheel position. If disassembly is required, use qualified service personnel..
Possible causes include uneven debris buildup, wheel misalignment, loose components, worn bearings, rubbing, or foreign material in the housing. Shut the equipment down and identify the source before returning it to service.
Static pressure is the airflow resistance created by filters, coils, ducts, dampers, and other system components. It affects the fan’s operating point and delivered airflow, so a replacement must match the system - not only the original wheel’s dimensions.
Only when permitted by the equipment design and manufacturer instructions. Increasing speed changes airflow and static pressure and can sharply increase motor power demand and sound. Use approved controls and verify the fan and motor operating limits.
