Pressurization and Depressurization Testing for Airtightness Excellence

When it comes to Passive House construction, one of the defining metrics is airtightness. Achieving superior airtightness not only contributes to energy efficiency but also ensures optimal indoor comfort and long-term durability.  At the heart of this airtightness verification lies an essential tool: The Blower Door.

In this post, we’ll dive into how blower doors are used during Passive House testing—particularly for both pressurization and depressurization—and why this dual approach is crucial to meeting the rigorous standards of Passive House certification.

What is a Blower Door?

A blower door is a diagnostic tool designed to measure the airtightness of buildings. It consists of a powerful, calibrated fan that mounts into an exterior door frame, along with pressure gauges and manometers to measure airflow and pressure differences.

By either blowing air into (pressurization) or sucking air out of (depressurization) a building, the blower door simulates pressure differences similar to those experienced in real-world weather conditions. This helps identify how much air is leaking through the building envelope and where.

The Passive House Standard and Airtightness

Passive House certification demands extremely low air leakage—specifically, no more than 0.6air changes per hour (ACH50) at a pressure differential of 50 Pascals. To meet this, a project must undergo blower door testing that includes both pressurization and depressurization phases.

But why both?

Pressurization vs. Depressurization

Pressurization Testing: The fan pushes air into the building, creating positive pressure. This forces indoor air out through leaks, allowing the detection of outward leakage paths.

Depressurization Testing: The fan pulls air out of the building, creating negative pressure. Outdoor air is sucked in through leaks, which can help identify different leakage paths than during pressurization.

Why test both?

Materials and assemblies may behave differently under positive vs. negative pressure. For instance, flexible air barriers might balloon inward under depressurization and outward under pressurization, potentially revealing flaws that only show under one condition.  Wind barriers, window seals, and mechanical penetrations can also respond differently to each pressure scenario.

Testing both ways provides a more comprehensive picture of the building’s performance and ensures that the airtightness is robust in all real-world conditions. 

Conducting the Testin Passive House Projects

1. Preparation

·        Close all exterior doors and windows.

·        Seal intentional openings like flues or trickle vents, as per Passive House protocols.

·        Turn off HVAC systems.

2. Setup

·        Install the blower door system into a main entryway.

·        Calibrate the equipment and establish baseline readings.

3. Testing

·        Perform a series of tests at multiple pressure points (typically ranging from 10 to 60Pascals).

·        Conduct both pressurization and depressurization sequences.

·        Record airflow rates at each pressure level.

4. Data Analysis

·        Use the data to calculate air changes per hour at 50 Pascals (ACH50).

·        Evaluate for consistency between pressurization and depressurization results.

·        Identify and address significant discrepancies that may indicate weak spots or design flaws.

Beyond the Numbers: Diagnostic Insights

Blower door testing isn’t just about passing certification—it’s a diagnostic goldmine. Using smoke pens, infrared cameras, or even a simple hand, testers can locate specific leak areas during the test. This allows teams to:

·        Pinpoint problem areas like poorly sealed windows, penetrations, or top plates.

·        Implement targeted sealing strategies.

·        Verify improvements with follow-up testing.

Conclusion

A blower door is more than a certification checkbox—it's a window into the health and performance of your building envelope. By using both pressurization and depressurization, Passive House builders and designers can gain valuable insight, ensure compliance, and push their projects to meet the highest standards in building performance.

If you’re committed to Passive House principles, don’t skimp on this step. Embrace the blower door, test thoroughly, and let airtightness be a source of pride in your high-performance home.

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