Residential Duct Leakage CFM25 (IECC Table R403.3.8)
Whether a residential duct system passes the energy-code tightness test.
Example
You enter
- Measured total leakage at 25 Pa (CFM25) 80
- Conditioned floor area (ft²) 2000
- Custom limit (CFM25 per 100 ft², Custom configuration only) 4
You get
- Normalized leakage 4.00 CFM25 / 100 ft^2
Checked against published worked examples from: BNP Media (The ACHR News); JADE Learning.
Details, formula, and sources
ScopeThe measured total leakage at 25 Pa (from a duct blaster) normalized to the conditioned floor area, CFM25 per 100 ft^2 = leakage / area x 100, against the IECC 2024 Table R403.3.8 limit for the test configuration and the number of ducted returns (4 with all components installed and fewer than 3 returns, 6 with 3 or more), or the 2021 limits. 80 CFM25 on 2,000 ft^2 gives exactly 4.0 -- a pass at the limit; a leakier 100 gives 5.0, a fail with two returns and a pass with three. A system serving 1,000 ft^2 or less is judged on total CFM25 instead. Distinct from the SMACNA leakage-class test for commercial duct. A field aid; the adopted energy code, the required test type, and the rater govern.
Formula or tablenormalized = leakage_cfm25 / cfa_ft2 x 100; limit from IECC 2024 Table R403.3.8 by configuration and ducted returns (3 / 4 / 6 / 8 per 100 ft^2 with fewer than 3 returns, 4 / 6 / 8 / 12 with 3 or more), or IECC 2021 R403.3.6 (3 / 4 / 8), or a custom limit; a system serving 1,000 ft^2 or less passes on total leakage <= 30 / 40 / 60 / 80 CFM25 under 2024.
Source and editionIECC 2024 §R403.3.7 (duct testing) and Table R403.3.8 (maximum total duct leakage) [§R403.3.5 / §R403.3.6 in IECC 2021], and the RESNET / ANSI 380 duct-leakage test method, by name.
Free accessIECC is viewable through the ICC public-access reader; the leakage / area x 100 normalization is public arithmetic.
What governsEstimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.
API field namesleakage_cfm25, cfa_ft2, limit, normalized
- Normalization CFM25 per 100 ft^2 = leakage / conditioned floor area x 100IECC 2024 §R403.3.7 [R403.3.5 in 2021]
- Limit by configuration IECC 2024 Table R403.3.8 by configuration, ducted returns and system size, IECC 2021 R403.3.6, or a custom limitIECC 2024 Table R403.3.8
- Rater governs the required test type and the rater's calibrated duct tester govern the official resultscope of this tile