Centrifugal Fan Selection Guide: Capacity, Pressure, Materials

Steps to Choose the Correct Centrifugal Fan

Selection should follow a fixed sequence rather than starting from the fan model number. Working through these points in order avoids the most common sizing mistakes seen in industrial installations.

1. Calculate the required air volume in cubic meters per hour based on room size, air changes per hour, or process exhaust requirements.
2. Add up the resistance of all ductwork, filters, dampers, and bends to determine total static pressure in pascals.
3. Check the operating temperature range, since fans rated for ambient air below 80 degrees Celsius cannot be used for hot gas extraction above 200 degrees Celsius without a high temperature variant.
4. Confirm the available motor power supply, as fans above 15 kilowatts often require three phase power rather than single phase.
5. Select the housing and impeller material based on whether the airstream carries dust, moisture, or corrosive vapors.

Determining the Capacity Your System Needs

Capacity, measured in cubic meters per hour or cubic feet per minute, is calculated from the volume of the space and the number of air changes required per hour for the application.

Oversizing capacity by more than 20 percent above the calculated requirement increases energy consumption without a proportional gain in ventilation effectiveness, while undersizing by even 10 percent can leave a system unable to meet air change targets during peak load periods.

Factors That Influence Operating Efficiency

Efficiency in a centrifugal fan is the ratio of useful air power output to electrical power input, and several design and installation factors determine how close a fan operates to its rated efficiency point.

Selecting Fans Based on Static Pressure

Static pressure requirements determine which fan class and impeller type can deliver stable performance under the actual resistance of the connected system, not just the open air rating shown on a basic spec sheet.

A fan selected only on airflow rating without checking the static pressure curve at that flow point can deliver as little as 60 percent of the expected airflow once connected to a system with higher than anticipated resistance, which is why the operating point should always be read from the fan curve rather than from the maximum rated values alone.

Material Grades for Different Operating Conditions

The housing and impeller material must withstand the chemical and physical properties of the air or gas being moved, since the wrong material grade can lead to corrosion failure or impeller imbalance within months of operation.

• Mild steel with epoxy or powder coating is suitable for dry, non corrosive air in general ventilation applications, offering a typical service life of 8 to 12 years.
• Galvanized steel provides additional protection in environments with intermittent moisture, such as parking garage exhaust or general outdoor installations.
• Stainless steel grade 304 is used where mild chemical exposure or food grade cleanliness is required, while grade 316 is selected for higher chloride exposure such as coastal or marine environments.
• Fiberglass reinforced plastic construction is used for handling acidic or alkaline fumes in chemical processing, resisting corrosion that would degrade metal housings within 1 to 2 years.
• Hardened or wear resistant steel impellers are specified for abrasive dust handling, extending impeller life from under 6 months with standard steel to 2 to 3 years in mining or grinding dust applications.