Blower door tests are a critical part of modern HVAC design. They measure how much air leaks in and out of a building, which directly affects heating and cooling loads. Properly documenting these tests is essential for permit submissions and AHJ approval.
Why Blower Door Documentation Matters
AHJs want to see that your Manual J load calculations reflect actual building conditions. Incorrect assumptions about infiltration can cause:
- Oversized or undersized equipment
- Rejected permit submissions
- Inaccurate energy usage predictions
Documenting blower door test results ensures that your calculations are defensible and that your project complies with professional standards.
Understanding Infiltration in Manual J
Infiltration is the uncontrolled air exchange through cracks, joints, and openings in a building envelope. It is typically measured in ACH50 (air changes per hour at 50 Pascals) or converted to CFM (cubic feet per minute) for load calculations.
Load Calc Guru Defaults:
- Uses an ACH interpolation based on building tightness and story distribution.
- Automatically calculates default infiltration values for load calculations.
However, field testing often shows that actual infiltration differs from software defaults. That’s where documenting your blower door test comes in.
Step 1: Conduct a Blower Door Test
Perform a blower door test according to standard procedures:
- Seal the building and set up the blower door fan.
- Measure the pressure differential and airflow.
- Record the ACH50 or CFM value.
Accuracy here ensures your load calculation is based on real conditions, not assumptions.
Step 2: Integrate Test Data Into Manual J
Load Calc Guru Pro users can override default infiltration values with measured CFM data. Steps:
- Open the project in Load Calc Guru.
- Enter the CFM value from your blower door test.
- Run the load calculation; the software will incorporate the measured value instead of the default.
Note: The PDF report will show the resulting infiltration-adjusted loads. It doesn’t label whether the CFM came from a test or default, but the loads reflect the entered value accurately.
Step 3: Present Data Clearly for AHJs
When submitting permits, include:
- The measured CFM value in your load calculation notes
- Room-by-room heating and cooling loads incorporating infiltration
- Any deviations from default assumptions
This makes it easy for AHJs to verify that your calculations reflect real-world building performance.
Step 4: Best Practices for Permit Submissions
- Include a brief statement describing how the infiltration value was determined.
- Use consistent room names and floor plan labeling.
- Keep all supporting documentation (blower door test sheet, project notes) available for inspection.
Load Calc Guru’s report generator consolidates this information into a clean PDF, reducing friction during the review process.
Common Mistakes to Avoid
- Ignoring measured data: Relying solely on software defaults may misrepresent the actual load.
- Mislabeling rooms: Ensure all conditioned spaces are properly named.
- Not noting deviations: If the test result differs from the default, include an explanation.
Following these guidelines will help AHJs understand and trust your calculations.
Why This Matters for Contractors
Accurate blower door documentation:
- Ensures HVAC systems are correctly sized
- Reduces the likelihood of permit rejections
- Builds credibility with clients and inspectors
By integrating measured infiltration into Manual J calculations using Load Calc Guru, you can produce professional, defensible reports quickly and reliably.
Action Step: If you haven’t yet measured your project’s infiltration, schedule a blower door test and enter the resulting CFM into Load Calc Guru. Your Manual J loads will reflect actual building conditions, giving AHJs confidence in your submission.