A Manometer is a precision pressure measurement instrument using a liquid column (typically water or mercury) to measure pressure differentials in HVAC systems. Manometers are essential diagnostic tools for verifying system airflow, filter conditions, and proper duct pressure balancing.
Types and Measurement Range
Inclined-tube manometers offer enhanced sensitivity for low pressures, measuring 0-10 inches of water column (in. W.C.) with 0.01 in. W.C. resolution. U-tube manometers measure ±20 in. W.C. with direct left-right liquid comparison. Digital manometers provide electronic readout of differential pressure, absolute pressure, or velocity pressure. Water column height of 1 inch W.C. equals 249 Pascals. Most HVAC applications require 0-5 in. W.C. range for duct and filter pressure drop verification.
HVAC Diagnostic Applications
Technicians measure filter pressure drop to determine replacement timing, typically replacing when drop exceeds 0.5 in. W.C. Duct system pressure balancing verifies branch duct pressures at 0.02 in. W.C. differential. Static pressure measurement at supply plenums indicates adequate airflow and coil loading. Return air plenum pressure confirms supply-return balance preventing room pressurization or depressurization.
Proper Usage
Manometer accuracy depends on proper leveling and zero calibration before each use. Liquid column must move freely without sticking or bubbles. Readings require 30 seconds for liquid stabilization at each measurement point. Digital manometers provide faster readings with automatic temperature compensation. Regular calibration against known pressure standards ensures measurement accuracy. Improper readings from dirty or tilted manometers lead to incorrect system adjustments and poor commissioning results.