Enter the fan flow rate (CFM), the total pressure (in. wg), and the fan power input (hp) into the calculator to determine the Fan Efficiency. 

Fan Efficiency Formula

The following formula is used to calculate the Fan Efficiency.

Efan = FR * Pt/ (6343 * Pi)*100
  • Where Efan is the Fan Efficiency (%)
  • FR is the fan flow rate (CFM) 
  • Pt is the total pressure (in. wg) 
  • Pi is the fan power input (hp) 

To calculate the Fan Efficiency, multiply the fan flow rate by the total pressure, then divide by the product of 6343 times the power input, then multiply by 100.

How to Calculate Fan Efficiency?

The following example problems outline how to calculate the Fan Efficiency.

Example Problem #1

  1. First, determine the fan flow rate (CFM). In this example, the fan flow rate (CFM) is given as 400 .
  2. Next, determine the total pressure (in. wg). For this problem, the total pressure (in. wg) is given as  30 .
  3. Next, determine the fan power input (hp). In this case, the fan power input (hp) is found to be 20.
  4. Finally, calculate the Fan Efficiency using the formula above: 

Efan = FR * Pt/ (6343 * Pi)

Inserting the values from above and solving yields: 

Efan = 400 * 30/ (6343 * 20) *100 = 9.45 (%)

Example Problem #2

Using the same method as above, determine the variables required by the equation. For this example problem, these are provided as:

fan flow rate (CFM) = 500

total pressure (in. wg) = 30

fan power input (hp) = 10

Enter these given values yields: 

Efan = 500 * 30/ (6343 * 10)*100 = 23.648 (%)