Industrial Fans, Blowers & Air Movement Equipment worked example

Inlet/Outlet Velocity at 66% effective open-area factor: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop effective open-area factor to 66%, then walk the calculation through step by step. Estimate effective inlet or outlet air velocity from airflow, opening area, and efficiency or blockage allowance.

The inputs for this scenario

  • Airflow through the opening: 12,000 CFM (held at the documented default)
  • Inlet or outlet free open area: 8 sq ft (held at the documented default)
  • Effective open-area factor: 66 % (the input this scenario stresses; the baseline uses 92)

Working through the calculation

  • The calculation starts from the formula this tool documents: Raw inlet or outlet velocity = airflow through opening รท inlet or outlet open area.
  • Effective inlet or outlet velocity works out to 990 ft/min at these inputs, and this is the headline figure for the scenario.
  • Raw inlet or outlet velocity works out to 1,500 ft/min at these inputs.
  • Open-area efficiency allowance works out to 66 % at these inputs.
  • Runtime works out to 8 hr at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where effective open-area factor sits at 92% and the headline result is 1,380 ft/min, this scenario comes in 28.26% below the baseline at 990 ft/min.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to effective open-area factor, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. It assumes uniform velocity across the face; in reality flow concentrates near the fan throat and separates at corners, so localized velocities can run well above the average.

Results at a glance

  • Effective inlet or outlet velocity: 990 ft/min (headline result)
  • Raw inlet or outlet velocity: 1,500 ft/min
  • Open-area efficiency allowance: 66 %
  • Runtime: 8 hr

Run it with your numbers

  • To rerun this with your own numbers, open the live Inlet/Outlet Velocity calculator, set effective open-area factor to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.