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HVAC & Airflow

Fan Static Pressure Calculator

System resistance a fan must overcome.

Enter your values

ⓘ Live results

Results
Total static pressure
0.68 in w.c.
In pascals
169
Largest component
duct
Select fan at
design CFM against 0.68 in w.c.

Quick answer

A fan must be selected at the system's total static pressure, not in free air, or delivered airflow falls short.

TSP = duct loss + filter + coil + grilles

How to use the Fan Static Pressure Calculator

  1. 1Enter each component's pressure drop at design airflow.
  2. 2Use a dirty-filter value, not a clean one, so the system still works months later.
  3. 3Select the fan from its curve at the total static shown.

Worked example

Using the values the calculator loads with:

Inputs

  • Duct loss0.25 in w.c.
  • Filter loss0.15 in w.c.
  • Coil loss0.2 in w.c.
  • Grilles and registers0.08 in w.c.

Results

  • Total static pressure0.68 in w.c.
  • In pascals169
  • Largest componentduct
  • Select fan atdesign CFM against 0.68 in w.c.

Frequently asked questions

Why does free-air CFM mislead?

Fan ratings in free air ignore the system; a 400 CFM fan may deliver 250 CFM once ducted.

What is a typical residential total?

Around 0.5 in w.c. is the design target for a standard air handler.

About this calculator

Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.