Duct Leakage Testing in Nantucket, MA — CFM25 Limits & Test Process (2026)
The Nantucket duct-tightness requirement, how the Duct Blaster test works, the CFM25 thresholds you must meet, and how to schedule a documented test.
Duct Testing Quick Facts — Nantucket
- Ducts must leak no more than 4 CFM25 per 100 sq ft of conditioned floor area.
- Testing is required when any duct runs outside conditioned space (attic, crawlspace, garage).
- Systems entirely within the thermal envelope may be exempt — we confirm before testing.
- Performed with a calibrated Duct Blaster and documented for your building department.
Why Duct Leakage Matters in Nantucket
Leaky ducts waste the energy your heating and cooling equipment produces — pushing conditioned air into attics and crawlspaces instead of living space. Massachusetts code limits that loss to 4 CFM25 per 100 square feet of conditioned floor area (measured at 25 pascals). Sealed ducts lower bills, improve comfort, and are required to pass the Nantucket energy code and complete a HERS rating.
Nantucket Duct Leakage Limits
| Test timing | Maximum leakage | Applies when |
|---|---|---|
| Rough-in (air handler installed) | ≤ 4 CFM25 / 100 ft² | Ducts outside conditioned space |
| Post-construction (final) | ≤ 4 CFM25 / 100 ft² | Standard verification point |
| Ducts fully inside envelope | Testing may be waived | All ducts in conditioned space |
This threshold is enforced under the Stretch Code that applies in Nantucket.
How the Duct Blaster Test Works
1. Seal Registers
- Cover supply/return grilles
- Connect Duct Blaster to system
2. Pressurize to 25 Pa
- Fan pressurizes ductwork
- Measure leakage (CFM25)
3. Compare & Document
- Normalize per 100 ft²
- Pass/fail vs 4 CFM25
- Signed report
Schedule Duct Testing in Nantucket
We perform certified duct leakage testing throughout Nantucket, typically alongside your blower door test and HERS rating. See the full Nantucket energy code requirements for how it all fits together.
Quick Answers — Nantucket Duct Testing
Schedule duct testing in Nantucket.
Talk to a certified Massachusetts HERS rater and get a free, no-obligation quote.
Call (617) 571-4368 Get a Free Quote