The Fan Static Efficiency Equation

Fan static efficiency is the measure of the airstream’s potential, or optimal energy consumption, as determined by the ratio of power output to the power supplied.

But what constitutes good efficiency? How does it impact your decisions and operations? It allows you to determine how much horsepower you need to achieve maximum static efficiency in your application based on volume, pressure.

Defining and Making the Calculation


Volume is the quantity or velocity of air, gas, and/or other materials moving through the fan as measured in cubic feet per minute (CFM).

Static Pressure

Static pressure indicates how much resistance the airflow needs to move through as measured in inches of water gauge (in. WG).

Horsepower (HP)

Horsepower is the measurement of energy in units of power. It indicates how much energy the motor will provide and how much energy the fan will consume given application-specific factors.

Conversion Constant

A conversion constant is a number used to normalize equations containing varied units of measurement, in this case, CFM and in. WG. The conversion constant for static efficiency is 6343.

The Static Efficiency Equation

Static efficiency is the product of the volume and pressure you need in your application divided by the product of the conversion constant and horsepower, as follows:

Why Fan Static Efficiency Matters

You can use the maximum static efficiency to determine the horsepower you need in your application.

For example, if you have an industrial fan that can achieve 80% static efficiency and you’re trying to move 20,000 CFM through 10 inches WG of resistance, a 40 horsepower motor would get the job done. In the same application, if you selected a less efficient fan with only 50% static efficiency, the calculation would indicate 63 HP, so you’d have to bump all the way up to a 75 HP motor to drive it.

You can also use the fan static efficiency calculation to determine what type of industrial fan is optimal for your application. The higher the volume relative to static pressure, the more likely it is that you can select a high-efficiency fan.

Hear it from an Application Engineer

Senior Application Engineer Chet White explains how to calculate static efficiency and why it matters in this 2-minute whiteboard tutorial.

When you’re ready to start your project or update your maintenance program, reach out, and connect with one of our application engineers to discuss the details of your project.

Related Content

For more information on fan static efficiency, check out these additional articles:

We welcome comments and questions via our LinkedIn Page, and you can always Contact Us or Request a Quote for more details.