Duct pressurization testing measures the amount of air leaking from ductwork by sealing the system and applying a controlled pressure differential. Technicians seal all registers, grilles, and terminals, then pressurize the duct system to 25 pascals (0.1 inch water column) using a blower door or similar device. Pressure drop rate indicates total leakage volume.
Test Methodology and Standards
The blower door measures airflow required to maintain constant pressure; this volume directly correlates to duct leakage in CFM. ASHRAE 152 and IECC codes establish maximum acceptable leakage at 15 percent of system airflow for residential ducts. Leakage exceeding 300 CFM indicates significant energy losses and comfort issues. The test typically takes 10-20 minutes per system zone.
Performance Implications
Duct leakage reduces heating and cooling efficiency by 10-30 percent while contributing to humidity control problems and uneven temperature distribution. Pressurization testing identifies whether leakage occurs in accessible or concealed sections, guiding repair prioritization. Results inform decisions regarding duct sealing, insulation upgrades, or replacement. This measurement proves essential for energy audits and new construction verification.