What is static pressure?

Static pressure is the pressure created by everything else in the ductwork that resists the airflow from the fan. This can include anything from the ductwork itself to the various dampers, coils, and other components installed in the system.

Static pressure is measured in “inches of water column” or simply “in. wc”.

When static pressure increases, the HVAC system must work harder to overcome it. This means the system must increase the volume of air it is pushing and which also increases the energy being used.

How much more energy is needed? The 3 Fan Laws can help which you can read about here. 

Why is static pressure measured in “in. wc”? Why not PSI?

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