What Is a Blower Door Test?
A blower door test is a diagnostic procedure that measures the air tightness of a building’s envelope. It’s required for new construction in most Massachusetts municipalities that have adopted the Stretch Energy Code — and failing it can delay your certificate of occupancy.
Here’s how it works: a calibrated fan is temporarily mounted in an exterior door frame. The fan depressurizes the building to a standard pressure of 50 Pascals (Pa). The airflow required to maintain that pressure is measured and divided by the building’s volume to calculate ACH50 — air changes per hour at 50 Pascals.
Massachusetts Blower Door Test Requirements
The Massachusetts Stretch Energy Code requires new residential construction to achieve 3.0 ACH50 or better. The standard Massachusetts Building Code (for towns that haven’t adopted the Stretch Code) requires 5.0 ACH50.
To put this in perspective: a typical older home in Massachusetts tests at 10-15 ACH50. Modern construction that passes the Stretch Code test is 3-5x more airtight than existing housing stock.
What Causes a Blower Door Test Failure?
The most common sources of air leakage in new construction are:
- Penetrations through the building envelope — pipes, wires, and ducts that pass through exterior walls, floors, or the ceiling/attic plane
- Attic hatch — often overlooked, must be weather-stripped and insulated
- Recessed lighting — must use airtight (AT) rated fixtures in insulated ceiling assemblies
- Band joists and rim joists — the connection between the foundation and framing is a major leakage point
- Window and door rough openings — must be properly flashed and sealed
- Top plates — the top of interior walls where they meet the ceiling/attic
- Electrical boxes on exterior walls
When Should You Schedule a Blower Door Test?
The blower door test must be conducted after the building is complete — all windows, doors, and mechanical penetrations must be installed and sealed. However, scheduling it before drywall is finished can be strategic: if you fail, it’s much easier to locate and seal air leaks before the walls are closed up.
Many experienced builders do an informal pre-drywall air sealing inspection and pressure test to catch problems early. We can help with this diagnostic process.
What Happens If You Fail the Blower Door Test?
If your test comes in above 3.0 ACH50, you’ll need to locate and seal additional air leaks before retesting. We use a variety of diagnostic methods to find leaks:
- Smoke pencils to visualize airflow around suspect areas
- Thermal imaging (infrared camera) to identify temperature differentials indicating leakage
- Pressure diagnostics to isolate which assemblies are leaking most
Most projects that fail can be brought into compliance with targeted air sealing — typically spray foam at penetrations, weatherstripping at the attic hatch, and caulk at top plates and band joists.
Blower Door Testing Costs in Massachusetts
Blower door testing is typically bundled with HERS rating services. Call (617) 501-6788 for a free quote. We offer same-day scheduling and work around your construction timeline across all 351 Massachusetts cities and towns.
Work With an Experienced Testing Partner
Home Energy Efficiency Consultants has performed blower door tests on thousands of Massachusetts new construction projects. Our owner has 25+ years of construction experience — so when we identify an air sealing problem, we can tell your crew exactly what to fix and how.
