Published: May 2026 | Blower DoorAir SealingMassachusetts
Failing a blower door test can cause delays on your construction project — but it’s more common than you think, and it’s almost always fixable. Here’s what to do if your home doesn’t pass.
What Does It Mean to “Fail” a Blower Door Test?
Under the MA Stretch Code, new residential construction must achieve 3.0 ACH50 or less. If the test result is above 3.0 ACH50, the home fails and must be air-sealed and re-tested before a certificate of compliance can be issued.
Common Causes of Blower Door Test Failures
- Attic bypasses: Gaps in the ceiling where interior walls meet the attic plane are the #1 source of air leakage in new construction.
- Top plates: Unsealed top plates at exterior walls create continuous air pathways.
- Band joists and rim joists: The area where the floor framing meets the foundation wall is frequently missed.
- Plumbing and electrical penetrations: Pipes and wires that penetrate the building envelope need to be sealed.
- Recessed lighting: Non-airtight recessed light fixtures in the ceiling create direct paths to the attic.
- HVAC penetrations: Duct boots, exhaust fan housings, and equipment curbs that penetrate the building envelope.
How to Find the Leaks
While the blower door is depressurizing the house, a technician can use smoke pencils, infrared thermal imaging, or just their hand near suspected leak points to identify where air is entering. Thermal cameras are particularly effective at finding insulation voids and major air leakage pathways.
How to Fix Blower Door Failures
Most failures can be corrected with a few hours of targeted air sealing. Effective sealants include:
- Spray foam: For larger gaps, penetrations, and rim joists
- Mastic sealant: For duct connections and HVAC penetrations
- Caulk: For smaller gaps around windows, doors, and plumbing
- Weatherstripping: For door gaps
How Many Re-Tests Do You Get?
There’s no limit on the number of re-tests, but each re-test may incur an additional fee. Most projects that fail their first blower door test pass on the first re-test after targeted air sealing.
Schedule Blower Door Testing in Massachusetts
If you’re approaching your blower door test — or need a re-test — HERS Rating Company provides fast, accurate testing for all 351 MA cities.
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