What static pressure means
The blower creates a pressure difference to move air through the system.
Static pressure is measured in inches of water column and compared with equipment specifications.
How it is measured
A manometer measures return-side and supply-side pressure through test ports.
Pressure drop across the filter or coil can identify the restrictive component.
Common causes
Undersized return ducts, restrictive filters, dirty coils, closed dampers, crushed flex duct, and poor transitions are common causes.
Increasing blower speed may worsen noise if duct capacity is inadequate.
Why it matters
High static can cause noise, weak airflow, uneven comfort, furnace limit trips, and frozen coils.
ECM motors may increase speed and energy use trying to maintain airflow.
Correction options
Solutions may include larger filter area, added returns, duct repairs, coil cleaning, grille changes, or blower adjustments.
Measurements should support the proposed correction.
Frequently asked questions
Can a dirty filter cause it?
Yes.
Can it damage a furnace?
It can contribute to overheating.
Can it freeze a coil?
Yes.
Is it the same as airflow?
No.
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