HVAC Ductwork, Air Handling & Mechanical Products worked example

Damper Sizing with duct opening width of 60 in: a worked example

Push duct opening width up to 60 in and the picture changes. This example computes every intermediate figure at that operating point. Use this when selecting a volume control damper, fire damper, or smoke damper for a rectangular duct connection. Enter the duct width and height to get the face area, then check whether your design CFM produces a face velocity within the allowable range for the damper type. AMCA and manufacturer data typically specify maximum face velocities for control dampers between 1500 and 2500 FPM.

The inputs for this scenario

  • Duct opening width: 60 in (raised for this scenario; the documented default is 24)
  • Duct opening height: 16 in (unchanged)
  • Design airflow: 1,800 CFM (unchanged)
  • Maximum allowable face velocity: 2,000 FPM (unchanged)

Working through the calculation

  • Applying the documented formula (Damper face area = (width × height) ÷ 144 (sq ft)) to the inputs above produces each figure below.
  • At this operating point the engine returns 3,456,000,000 units for result, the number this scenario is built around.
  • At this operating point the engine returns 1,728,000 value for base product.
  • At this operating point the engine returns 2,000 x for multiplier.
  • At this operating point the engine returns 960 value for factor a x b.

How this compares with the baseline

  • Against the tool's baseline example, where duct opening width sits at 24 in and the headline result is 1,382,400,000 units, this scenario comes in 150% above the baseline at 3,456,000,000 units.
  • It computes damper face area from the opening dimensions, the design face velocity from airflow, and the margin against your maximum allowable face velocity. The value of this scenario is the size of the gap it exposes: that gap, priced out over a year, is the budget you can justify spending to close it.

Results at a glance

  • Result: 3,456,000,000 units (headline result)
  • Base product: 1,728,000 value
  • Multiplier: 2,000 x
  • Factor A x B: 960 value

Run it with your numbers

  • Every input above is editable in the live Damper Sizing calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.