Duct External Static Pressure (ESP) Calculator

This Calculator estimates the External Static Pressure Loss through a linear length of Duct for duct systems sized based on frictional loss. In order to size a fan's ESP, consider only the length of duct along the route with the largest pressure drop.

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Air Duct

The total fan ESP should overcome the system pressure drop, which should be the sum of pressure drop due to friction of air along the duct, and all losses through duct accessories and equipment such as dampers and grilles. Along the length of ducts with the greatest loss, only ONE terminal grille (exclude the branches) but ALL in-line dampers are to be considered.

A general example of pressure drop of few types of duct accessories are shown below. The higher the "restriction" of the accessories to the airflow of the duct system, the higher the pressure drop of the system across the accessory.

Accurate data on Pressure Drop shall always be retrieved from individual product datasheet for each type of accessories and their installation configurations, air flow and acceptable noise level.