PerformanceUp to date · Jan 15, 2026
ACH50 (Air Changes per Hour at 50 Pascals)
The number of times the total air volume of a house is exchanged per hour when the house is depressurized to 50 Pascals (about 0.2 inches of water column) during a blower door test.
Why It Matters
ACH50 is the standard air tightness metric. An older leaky house might measure 12-15 ACH50; an energy-efficient new home targets 3 ACH50 or less; Passive House requires under 0.6 ACH50.
Related Topics
Related Terms
Blower Door Test
A diagnostic test that uses a calibrated fan mounted in an exterior doorway to depressurize the house and measure the total air leakage rate, expressed in CFM50 or ACH50.
Air Sealing
The process of identifying and sealing unintentional air leaks in a building envelope — including gaps around pipes, wires, ducts, windows, and the attic hatch.