Can I enter an SI leakage class?

No, this model uses the US leakage-class convention with CFM, square feet and inches of water column. Enter measurements and a project class on that same basis.

Why does duct surface area matter?

Leakage class normalizes flow to 100 square feet of tested duct surface. The same leakage flow represents a lower class when the tested surface area is larger.

Can I enter zero measured leakage?

Yes, zero recorded flow gives a calculated class of zero. That arithmetic does not establish that actual leakage is zero; instrument resolution and test corrections remain part of your record.

Does a positive margin prove compliance?

No, it only compares your entries with the entered class allowance. Applicable specifications, test quality, measurement uncertainty and acceptance decisions still require review.

HVAC Ductwork, Air Handling & Mechanical Products calculator

Duct Leakage Class Comparison Calculator

Find the leakage class represented by your recorded airflow, duct area and test pressure. Enter the project's specified class to see the corresponding allowance and flow margin.

What this calculator does

Compare measured duct leakage with the leakage class specified for your project.

Formula used

Measured class = 100 × leakage CFM ÷ tested ft² ÷ pressure^0.65
Leakage at specified class = specified class × pressure^0.65 × tested ft² ÷ 100
Flow margin = leakage at specified class − measured leakage

Inputs explained

Measured Leakage: Corrected leakage flow from the applicable test record.
Tested Duct Surface Area: Surface area of tested ductwork, excluding temporary blanking plates.
Test Pressure: Positive pressure magnitude recorded on the applicable test basis.
Specified Leakage Class: Leakage class from your applicable project specification.

How to use the result

Best suited to recorded duct leakage comparison, project leakage allowance review.
Does not select a leakage class, validate test measurements or certify compliance. Does not establish safe test pressure, duct strength or a testing procedure. Listed input ranges are software limits, not equipment ratings or recommended operating conditions.

Current U.S. benchmarks

Industrial electricity averages 9.77 cents per kWh across the U.S. (EIA, Jul 2026), up 4.7% from a year earlier. Energy-intensive steps carry this directly into unit cost.
U.S. housing starts run at 1,275k per year (Census, Aug 2026), down 1.2% from a year earlier, the demand driver for building products.

Common questions

Can I enter an SI leakage class? No, this model uses the US leakage-class convention with CFM, square feet and inches of water column. Enter measurements and a project class on that same basis.
Why does duct surface area matter? Leakage class normalizes flow to 100 square feet of tested duct surface. The same leakage flow represents a lower class when the tested surface area is larger.
Can I enter zero measured leakage? Yes, zero recorded flow gives a calculated class of zero. That arithmetic does not establish that actual leakage is zero; instrument resolution and test corrections remain part of your record.
Does a positive margin prove compliance? No, it only compares your entries with the entered class allowance. Applicable specifications, test quality, measurement uncertainty and acceptance decisions still require review.

Last reviewed 2026-10-12.