Centrifugal Fans Explained: Choosing the Right Blade Design for Maximum Performance

Types, Applications, Selection

Centrifugal fans power industrial ventilation across virtually every sector, generating high static pressures to move air through ductwork, filters, and system resistance. Understanding blade designs, from high-efficiency airfoil wheels to rugged radial configurations, helps to make the best selection for your application. Learn how centrifugal fans work, explore different wheel types, and discover how to choose the right design for maximum efficiency, reliability, and performance in your facility.

How Centrifugal Fans Work to Build Static Pressure

Centrifugal fans operate on a simple, powerful principle: converting rotational energy into airflow and pressure. The process begins when a motor drives an impeller (wheel), causing its blades to rotate. This rotation draws air axially into the center of the impeller.

From Impeller to Volute: Converting Velocity to Pressure

As air enters the spinning impeller, centrifugal force accelerates it outward along the blade surfaces. The high-velocity air is then collected by the volute (scroll housing), a specially shaped casing that gradually expands in cross-sectional area. This expansion slows the air down, efficiently converting its kinetic energy (velocity pressure) into potential energy (static pressure). It is this static pressure that provides the force needed to push air through system resistance.

The Role of Fan Laws and Variable Frequency Drives (VFDs)

Fan performance is governed by a set of principles known as the Fan Laws, which dictate how changes in speed, diameter, and density affect airflow, pressure, and power consumption. A key takeaway is that a small change in fan speed results in a significant change in performance. This is why Variable Frequency Drives (VFDs) are so effective. By adjusting the motor's speed to match the system's exact demands, a VFD can deliver substantial energy savings and give you precise control over your ventilation system.

Centrifugal Fan Types and Performance

Airfoil and Backward Inclined Fans for High Efficiency

Airfoil fans represent the pinnacle of centrifugal design, achieving mechanical efficiencies up to 90%. Their blades feature a curved, aerodynamic profile (similar to an aircraft wing), reducing turbulence for smoother airflow. This makes them perfect for clean air applications where energy costs are a primary concern, such as commercial HVAC and clean process ventilation.

Backward inclined fans feature single-thickness blades angled away from the direction of rotation. While slightly less efficient than airfoil designs (typically 75-80%), they offer similar high-pressure performance with a greater tolerance for airstreams containing light, non-sticking dust.

Backward Curved Fans for Balance and Durability

Backward curved fans bridge the gap between high-efficiency designs and rugged industrial models. Their blades curve away from the direction of rotation, providing good structural strength while achieving efficiencies of 70-75%. They can handle light to moderate dust loads better than airfoil or backward inclined designs, making them a versatile choice for general industrial ventilation and HVAC systems where air may not be perfectly clean.

Radial Fans for Material Handling and Abrasive Airstreams

Also known as paddle-wheel fans, Radial designs feature blades that extend straight out from the hub. This simple and robust configuration prioritizes durability and material handling over efficiency (typically 60-65%). The wide spacing between blades resists clogging, allowing the fan to convey abrasive, sticky, or particulate-laden air. They are the workhorses for material conveying, dust collection, and high-temperature exhaust systems.

Common Applications by Environment and Air Quality

The versatility of centrifugal fans allows them to serve critical functions across nearly every industry. Matching the fan type to the environment is key to long-term success.

Clean Air Systems and Commercial HVAC

For commercial HVAC and clean manufacturing processes, efficiency and low noise are important factors. High-efficiency airfoil and backward inclined fans are the standard choice, moving large volumes of air while minimizing energy consumption and operational sound.

Industrial Ventilation with Light to Moderate Particulate

General manufacturing facilities often require fans for fume exhaust, dust collection, and general ventilation where the air is not perfectly clean. Backward inclined and backward curved fans provide a durable, efficient solution that can handle light dust loads without compromising performance.

Demanding Environments: Corrosive, High-Temp, and Material Conveying

In the toughest environments, durability is non-negotiable.

• Chemical and Wastewater Plants: Require fans made from corrosion-resistant materials like FRP or stainless steel to withstand acids, caustics, and other harsh chemicals.
• High-Temperature Applications: Found in power generation and heavy industry, these demand robust fans, often radial blade designs, built to endure extreme heat.
• Material Conveying: Mining, agriculture, and woodworking facilities rely on radial blade fans to move abrasive or sticky materials without clogging.

Selecting the Right Centrifugal Fan

Proper fan selection is a systematic process that balances performance requirements, efficiency, and environmental conditions to achieve a long-lasting fan and controlled operating costs.

Pre-Selection Checklist

Before you begin, gather the following system inputs:

• Define required airflow volume (CFM).
• Calculate total system static pressure.
• Characterize air quality and particulate type.
• Determine operating temperature range.
• Identify necessary materials of construction.
• Measure available physical space constraints.
• Specify maximum allowable noise levels.
• Select control method (VFD or constant).
• Confirm available power source and voltage.
• List all regulatory compliance needs.

Calculating Your Airflow (CFM) and Static Pressure Needs

Your first step is to define the required airflow (CFM) based on space volume, air change rates, or process needs. Next, calculate the total system resistance (static pressure) by adding up friction losses from ductwork, filters, hoods, and other components. Underestimating static pressure will result in poor airflow, while overestimating it wastes energy.

Matching Fan Design to Your Operating Point (BEP)

With your CFM and static pressure defined, you can select a fan. Choose a blade design that matches your air quality. Then, using the fan curve, select a fan size and speed so that your operating point is near the fan’s Best Efficiency Point (BEP). Operating near the BEP maximizes energy efficiency, minimizes noise, and reduces stress on the fan components, extending its service life.

Key Material and Construction Considerations

Finally, consider the operating environment. Extreme temperatures, corrosive gases, or explosion hazards will dictate the necessary materials of construction (e.g., FRP, stainless steel, special coatings) and motor specifications. Quality bearings, sized for the load and speed, are also crucial for reliable service with routine lubrication.

Frequently Asked Questions

What are the key differences between airfoil, backward inclined, and radial blade centrifugal fans?

Understanding centrifugal fan selection means knowing how designs impact performance. Airfoil vs radial fan: airfoil and backward inclined blades deliver top energy efficiency for clean air, while backward curved types balance efficiency with some dust tolerance. Radial fans excel where durability and material handling are key, especially in harsh or dusty environments. 

How do I select the right centrifugal fan for my facility's needs?

Effective centrifugal fan selection starts by calculating required airflow (CFM) and static pressure. Factor in air quality, temperature range, and materials of construction. Use a fan curve to identify models operating close to your best efficiency point (BEP) for higher performance, lower costs, and longer service life. Consider VFD control for flexible speed and energy savings.

Why is operating a fan near its Best Efficiency Point (BEP) important?

Operating near the best efficiency point (BEP) on the fan curve maximizes energy efficiency and minimizes noise and wear, which extends system life. Centrifugal fans matched to their BEP have lower operating costs and better reliability. VFD control helps keep your system at its BEP, even as conditions change.

Why Choose Hartzell Air Movement?

Hartzell Air Movement combines over 150 years of experience with innovative designs like precision-balanced one-piece impellers and application-specific construction. Our centrifugal fans deliver verified performance across industries including chemical processing, HVAC, food manufacturing, and heavy industry. The investment in proper selection pays dividends through reduced energy costs, minimal maintenance, and reliable performance over decades of operation.

Ready to select the optimal centrifugal fan for your application? Contact Hartzell's engineering team to discuss your requirements or request a performance curve review. Our team will help match the right fan design, materials, and configuration to your operating conditions, so you get efficient, reliable air movement customized to fit your needs.