Estimate the total external static pressure a fan must overcome — duct friction, fittings, filters, coils and diffusers all added up — to select the right fan.
traqR keeps your mechanical jobs, commissioning figures and service records against each site so the numbers stay with the system.
Start free trialMultiply the total effective length — straight duct plus the equivalent length of fittings — by the friction rate in Pa per metre.
Filters, coils and grilles each drop pressure. Add their pressure drops (using dirty-filter figures to be safe) to the duct loss.
The total external static pressure is what the fan must develop at the design airflow. Select a fan whose curve meets that duty with margin.
External static pressure (ESP) is the total resistance a fan must overcome to push air through the ductwork, filters, coils and grilles of a system, measured in pascals or inches of water gauge. The fan has to be selected to deliver the design airflow against that pressure.
Add the duct friction loss (effective length × friction rate) to the pressure drops across the components — filter, coil, grilles and any other equipment in the airstream. This tool sums those to give the total external static pressure and converts it to inches of water gauge.
A filter’s resistance rises as it loads with dust, so sizing on the clean-filter figure leaves the system short of airflow before the filter is due for a change. Using the dirty (final) pressure drop ensures the fan still delivers the design flow near end of filter life.
No. It’s a simplified estimate to help select a fan and sanity-check a system. A detailed calculation traces the full index run with actual fitting losses and component data, to a recognised method and standards such as AS 1668.
This calculator is a simplified estimate of external static pressure for guidance and fan selection. Detailed pressure-loss calculation should use actual fitting losses and component data to a recognised method, by a competent HVAC designer.
traqR keeps mechanical jobs and commissioning records against each site so the numbers stay with the system. Try it free for 14 days.