Duct Leakage Loss Calculator
Use the Duct Leakage Loss Calculator. Enter System airflow and Leakage percentage for a clear result, formula explanation, and practical planning checks.
Duct Leakage Loss measurements
Enter your values, then calculate.
Result
How to calculate duct leakage loss
This calculator finds duct leakage loss by multiplying total system airflow by the leakage percentage — quantifying how much conditioned air is being lost through duct leaks rather than reaching its intended destination.
How the calculation works
Leakage loss = System airflow × (Leakage percentage ÷ 100).
Example
A 1,200 CFM system with 15% duct leakage: Leakage loss = 1,200 × 0.15 = 180 CFM lost.
Frequently asked questions
How much duct leakage is normal?
Older, unsealed ductwork commonly leaks 15-25% or more of system airflow. Modern code-compliant systems that are properly sealed and tested can achieve leakage under 6%. An actual duct leakage test is the only reliable way to know your specific system's rate.
Duct Leakage Loss Calculator
Leakage loss = System airflow × (Leakage percentage ÷ 100).
Let's understand your duct leakage loss result.
Calculate a result above and this guide will help you interpret it using this calculator's own formula and explanation.
Pro Tips for Duct Leakage Loss
- Duct leakage in the 15-25% range is unfortunately common in older, unsealed duct systems; well-sealed modern systems can achieve under 6%.
- Duct sealing (mastic or foil tape at joints) is often a cost-effective efficiency improvement given how much conditioned air can be lost to leakage.
Common Duct Leakage Loss Mistakes to Avoid
- Assuming duct leakage is negligible without an actual duct blower door test, since leakage rates vary enormously and are often underestimated by eye.
When to Use This Calculator
This calculator finds duct leakage loss by multiplying total system airflow by the leakage percentage — quantifying how much conditioned air is being lost through duct leaks rather than reaching its intended destination.