Step-by-Step Procedure
Set Up Blower Door
- Install the blower door in an exterior doorway and depressurize the house to –25 Pa relative to outside.
Connect Duct Tester
Attach the DucTester fan to the return duct using a sealed flange and flex duct.
Seal all other supply and return registers to isolate the system.
Use Two Gauges
Gauge A monitors house interior pressure (maintained at –25 Pa).
Gauge B measures duct pressure relative to the house.
Depressurize Duct System
Turn on the DucTester and adjust its fan speed until the duct system reads 0 Pa relative to the house.
This means both house and duct are –25 Pa relative to outdoors.
Record Leak Flow
- Gauge B displays the CFM value required to maintain duct pressure at 0 Pa—this is the leakage to outdoors value.
Why this Method Works
Direct measurement of outdoor leakage: Only air leaving into unconditioned space is captured.
Stable testing environment: Depressurizing the house ensures a clear pressure boundary.
Two-gauge accuracy: Separating house and duct pressure readings avoids confusion or overlap from single-gauge setups.
Tips & Best Practices
Seal thoroughly: Ensure all vents are tightly sealed before starting to prevent measurement errors.
Stabilize readings: Allow ~60 seconds for pressures to settle after adjustments.
Gauge configurations: Make sure each gauge is on the correct mode and pressure channel—Channel A for pressure, B for flow.
