Advanced Calculator Inputs
Enter test pressure, duct area, measured leakage, leakage class, and reporting controls. Results appear above this form after submission.
Formula Used
Allowable Leakage = F × A ÷ 100
Actual CL = Measured Leakage × 100 ÷ A ÷ P0.65
F is the leakage factor in cfm per 100 ft². CL is the selected leakage class. P is test pressure in inches water gauge. A is tested duct surface area in ft². The calculator also applies safety margin and instrument uncertainty for a conservative pass check.
How to Use This Calculator
- Enter the project name and duct section.
- Select a surface area method.
- Add duct dimensions or manual surface area.
- Enter the test pressure and measured leakage.
- Select the target leakage class.
- Add design airflow, margin, and uncertainty if needed.
- Press the calculate button.
- Download the CSV or PDF report.
Example Data Table
| Section | Duct Type | Area ft² | Pressure in. wg | Target Class | Measured cfm | Expected Result |
|---|---|---|---|---|---|---|
| Supply Main A | Rectangular | 850 | 2.0 | 12 | 95 | Review margin |
| Return Riser B | Rectangular | 620 | 1.5 | 24 | 118 | Likely pass |
| Round Branch C | Round | 410 | 3.0 | 6 | 44 | Close check |
| Exhaust D | Mixed | 930 | 4.0 | 12 | 165 | Needs sealing review |
SMACNA Duct Leakage Testing Guide
Why Leakage Matters
Duct leakage changes system performance. It can waste fan energy. It can reduce delivered airflow. It can also create balancing problems. A leakage test gives a measured value. That value can be compared with a selected leakage class. This makes the review more consistent. It also helps teams document field quality before ceiling closure or final commissioning.
What the Calculator Measures
This calculator estimates allowable leakage from surface area, pressure, and leakage class. It also calculates actual leakage class from measured airflow. The result shows pass or fail status. It includes a conservative check when instrument uncertainty is entered. A safety margin can also be applied when a project needs stricter internal acceptance.
Pressure and Surface Area
Pressure is important because leakage changes with pressure. The formula uses pressure raised to the 0.65 power. Surface area is also important. A larger tested section can have a larger allowable leakage value. The calculator lets you enter area manually. It can also estimate area from rectangular or round duct dimensions.
Reading the Results
Start with the status banner. A pass means the conservative measured leakage is not above the adjusted limit. Then review actual leakage class. Lower class values indicate tighter ductwork. Check the leakage percentage of design airflow for context. This percentage is not a substitute for the class check. It is a useful operating indicator.
Using Reports
The CSV file is useful for logs and spreadsheets. The PDF file is useful for a submittal package. Keep the test pressure, duct area, measured leakage, and notes with the report. These details help another reviewer understand the test conditions. They also support later troubleshooting when system airflow does not match the design intent.
FAQs
1. What is a SMACNA duct leakage class?
It is a leakage rating based on airflow leakage per 100 square feet of duct surface at a pressure basis. Lower values usually mean tighter duct construction.
2. What unit should I use for pressure?
You can enter inches water gauge or pascals. The calculator converts pascals to inches water gauge before applying the leakage formula.
3. What does allowable leakage mean?
Allowable leakage is the maximum leakage airflow for the entered duct area, pressure, and selected leakage class before any safety margin is applied.
4. Why does the calculator use pressure to the 0.65 power?
The exponent models how leakage airflow changes with pressure. It is commonly used for duct leakage class calculations and pressure normalization.
5. What is conservative measured leakage?
It is the measured leakage increased by the instrument uncertainty percentage. This helps create a stricter pass or fail decision.
6. Can I use a custom leakage class?
Yes. Select custom and enter the required leakage class from project specifications, commissioning criteria, or engineering direction.
7. Is leakage percentage of airflow the main acceptance test?
No. The class-based comparison is the main result here. Leakage percentage of airflow is added only as a practical reference value.
8. Why download both CSV and PDF reports?
CSV is best for data records and spreadsheets. PDF is better for sharing a readable field report with the project team.