Glossary · Testing & air leaks

Duct leakage test

Also called: duct blaster test · Duct Blaster · duct pressurization test · duct tightness test · duct leakage · CFM25

A test that pressurizes your heating and cooling ducts with a calibrated fan to measure how much air escapes through leaks.

What it means

The tester seals the supply and return registers, connects a calibrated fan (often called a duct blaster) and holds the ducts at 25 pascals. The airflow needed to hold that pressure is the leakage, reported as CFM25. Total leakage counts every leak; a second version, leakage to outside, counts only air lost to attics, crawlspaces, garages or outdoors.

Why it matters in an audit

Leaky ducts waste heating and cooling you've paid for and can pull dusty or humid air from attics and crawlspaces into the house, so duct sealing is often a high-ranked audit recommendation.

Typical numbers

Reference values with their sources. Your auditor’s report gives the figure for your own house.

What	Value	Source
Typical loss in US homes (ENERGY STAR)	About 20%–30% of the air moving through the duct system	energystar.gov ↗
US energy code, new homes (2021 IECC)	Total leakage 4 CFM25 or less per 100 ft² of conditioned floor area, or 3 if tested at rough-in without the air handler	energycodes.gov ↗
ENERGY STAR new homes (Version 3)	Rough-in ≤ 4 CFM25 per 100 ft² or 40 CFM25; final ≤ 8 CFM25 per 100 ft² or 80 CFM25, whichever is greater	basc.pnnl.gov ↗

In the United States

ENERGY STAR lists ducts located in an attic, crawlspace or garage as a warning sign of duct problems, and recommends sealing with mastic or metal tape, never duct tape.

Sources

Learn more here

Duct leakage testing →

Related terms

Duct leakage to outside The part of duct leakage that escapes outside the heated and cooled space, into attics, crawlspaces, garages or outdoors.
Blower door test A test that uses a powerful, calibrated fan in an outside doorway to pull air out of the house and measure how leaky it is.
Pascal (Pa) and "50 Pa" A small unit of air pressure; airtightness tests hold a house at 50 pascals, about 1/2,000 of normal air pressure, so results can be compared.
Ducted heat pump A heat pump that heats and cools through ductwork, like central air conditioning, either on its own or paired with a furnace.
Air sealing Blocking the hidden gaps where air leaks in and out of a house, which cuts drafts, heating and cooling costs, and moisture problems.
Manometer A precise pressure gauge auditors use to read small pressure differences, in pascals, during blower door, duct leakage and combustion safety tests.
Manual D (ACCA duct design) The US industry standard for designing and sizing a home's ducts so each room gets the airflow the heating and cooling equipment is meant to deliver.

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