Learn what HVAC static pressure means, where resistance comes from and why excessive pressure can reduce blower airflow and system performance.
Static pressure is commonly described as the resistance the blower works against while moving air through the HVAC system.
Filters, coils, transitions, ducts, dampers, grilles and registers all contribute resistance. The blower's ability to maintain airflow depends on its performance characteristics at that pressure.
A system can have a powerful blower yet still deliver poor airflow if system resistance is excessive.
Pressure measured across the external air-distribution path of the equipment according to the relevant procedure.
Resistance added by the air filter.
Resistance as air passes through the indoor coil.
Positive pressure on the discharge side of the blower.
Negative pressure relative to ambient on the return side.
Airflow generally changes as static pressure changes.
Many service symptoms are easier to understand when you know what the system is trying to do. Pressure, temperature, airflow, heat transfer and controls are connected; a change in one can affect several measurements elsewhere in the system.
Professional HVAC diagnosis may require electrical meters, refrigeration gauges and temperature probes, airflow or static-pressure instruments, combustion analyzers and manufacturer-specific procedures. The Academy explains the concepts without encouraging unsafe internal testing.
Connect pressure, temperature and phase change.
Understand the air side of the system.
Review the complete system in homeowner terms.
Look up unfamiliar HVAC terminology.
Use the Learning Center for homeowner-focused explanations, the Troubleshooting Center for symptoms, and the Buying Guides when you are evaluating equipment or proposals.
Connect the technical concept to the complete residential system.
Look up related components, measurements and trade terminology.