It measures leakage under defined test conditions
A duct-leakage test uses a calibrated fan and pressure measurements to evaluate how much air escapes through openings in the tested duct system. The result can help identify a repair opportunity or verify completed sealing. It is not, by itself, a measurement of your utility savings or the air reaching each room.
PNNL's duct-leakage testing guide describes different test configurations. Ask which test is proposed and what decision it will inform. A useful report names the system, test boundary, pressure, and units rather than presenting a bare percentage with no explanation.
duct-leakage testing guide · Source checked 2026-09-07
Distinguish total leakage from leakage to outside
Total leakage includes openings to all spaces around the tested ducts. Leakage to outside concerns air crossing out of the home's air barrier, including into an unconditioned attic or crawlspace. “Outside” therefore does not only mean open sky.
PNNL's leakage-to-outdoors guide explains the use of house and duct pressure measurements to distinguish this leakage. The location matters: a hole in a duct within conditioned space has different consequences from one drawing air from an unconditioned attic. Even interior leakage can affect distribution, so a small outside-leakage result does not prove that the ducts serve every room well.
leakage-to-outdoors guide · Source checked 2026-09-07
Read the units before judging the number
CFM means cubic feet per minute. A result labeled CFM25 is airflow at a test pressure difference of 25 pascals. Reports may also divide leakage by conditioned floor area or another defined reference. Ask for both the measured result and any normalized calculation.
For example, a hypothetical report with 100 CFM25 and 2,000 square feet has 5 CFM25 per 100 square feet: 100 divided by 2,000, multiplied by 100. That arithmetic does not say the home loses 5% of its heating or passes a local requirement. It simply expresses the same test result relative to floor area. The applicable criterion and test method must be stated separately.
Request the details needed for a fair comparison
Keep this record for each tested system, especially if the home has more than one air handler. Have the tester explain anything excluded or temporarily sealed as part of the procedure.
| Report field | Why it matters |
|---|---|
| Test type | Total leakage and leakage to outside answer different questions |
| Boundary | Identifies the ducts, air handler, and components included |
| Conditions | Records test pressure, setup, and relevant limitations |
| Result | Shows units and any denominator used for a normalized figure |
| Criterion | Names the applicable program, code, or agreed repair target |
| Comparison | Makes before-and-after results traceable to comparable methods |
A new-construction program limit is not automatically the legal requirement for an existing-home repair. Ask the professional to identify the rule applicable to your location and scope.
Pair the test with an inspection and airflow checks
A leakage result will not locate every defect or tell you whether a branch is crushed, undersized, or poorly balanced. Inspection and room airflow measurements address those other questions. A sealed duct can still have excessive resistance or deliver too little air to a bedroom.
ENERGY STAR's duct-sealing guidance identifies damaged connections and hard-to-condition rooms as reasons to investigate. Ask the contractor to connect each recommended repair to a finding: a disconnected branch, a leaking joint, or a return problem. Our closed-bedroom guide covers the separate question of return paths.
ENERGY STAR's duct-sealing guidance · Source checked 2026-09-07
Define what the repair price includes
Ask which sections will be accessed, how hidden or inaccessible ducts will be handled, and whether damaged insulation or outer coverings are included. If a sealing method is proposed for inaccessible areas, ask what it can address and what physical repairs still require access.
Specify retesting before agreeing to the work. Request a final result using a comparable method, a list of repairs completed, and an explanation of any remaining leakage. Keep cosmetic restoration and access work visible in the quote so bids describe the same job. A savings estimate should state its assumptions rather than treating test leakage as a direct energy-loss percentage.
Use the result to make the next decision
For a heat-pump replacement, leakage is one part of assessing the existing air distribution. Combine it with the proposed equipment's airflow and pressure requirements using our duct-reuse guide. If the question is leakage through the house itself, ask about a blower-door test.
When requesting a ductwork inspection, describe the comfort problem and ask whether testing will help define the repair. That keeps the measurement tied to a useful decision instead of buying a report without a next step.
Editorial review: 2026-09-07