Diagnostic Service
Blower Door Testing
Quantify air leakage. Locate bypasses. Verify results.
The Most Useful Diagnostic Tool in Building Science
A blower door test measures the total air leakage of a building under controlled pressure conditions. It tells you — with a single number — how leaky a house is. Combined with a systematic inspection, it tells you where the leakage is and what to do about it. We use blower door testing as part of our Home Performance Assessment, as a standalone diagnostic service, and as a verification tool after corrective work is complete.
The Process
How a Blower Door Test Works
A calibrated fan is temporarily mounted in an exterior door frame. The fan depressurizes the house to a standard reference pressure — typically 50 Pascals below outdoor pressure. At that pressure, the fan's airflow rate equals the building's total air leakage rate. The result is expressed as CFM50 (cubic feet per minute at 50 Pascals) or ACH50 (air changes per hour at 50 Pascals).
Setup
The blower door frame and fan are mounted in an exterior door. Interior doors are opened; HVAC systems are temporarily shut down. The test takes about 15 minutes to set up.
Depressurize
The fan draws air out of the house, creating a uniform negative pressure throughout. This amplifies all air leakage pathways — making them detectable by feel, smoke, or thermal imaging.
Measure
The fan's airflow rate is measured at the reference pressure. This gives the total leakage number — CFM50 and ACH50 — which can be compared to code requirements, program standards, or baseline measurements.
Locate
While the house is under pressure, we walk the building systematically — using thermal imaging, smoke pencils, and our hands — to locate the specific bypasses and leakage pathways driving the number.
Diagnostic Value
What the Test Tells You
Total Air Leakage
A single, objective number that characterizes the building's overall tightness. Useful for comparing to code requirements, program thresholds, or your own baseline.
Where the Leakage Is
With the house under pressure, leakage pathways become detectable. Thermal imaging and smoke reveal bypasses that are invisible under normal conditions.
Where to Focus Corrective Work
Not all leakage pathways are equal. The test helps prioritize which bypasses to address first for the greatest improvement in comfort and energy performance.
Whether Corrective Work Performed
A post-work blower door test confirms that air sealing and insulation improvements actually reduced leakage — and by how much. This is the only way to verify results objectively.
North Country Climate
Why Air Leakage Matters More in the North Country
In a cold climate, air leakage is the dominant mechanism of heat loss — more significant than conduction through walls or ceilings in most existing homes. Stack effect in a North Country winter is powerful: warm air rises and escapes through the top of the house while cold air infiltrates at the bottom. Every bypass in the attic floor, every unsealed penetration, every gap at the rim joist is a direct pathway for heat to leave and cold to enter. Reducing air leakage is almost always the highest-return improvement available in an existing North Country home.
Services & Pricing
Blower Door Testing Services
As Part of a Home Performance Assessment
Blower door testing is included in our Home Performance Assessment when conditions warrant. The assessment also includes a building-envelope inspection, thermal imaging, moisture observations, and written findings with prioritized recommendations.
Book a Home Performance AssessmentStandalone Blower Door Test
A standalone blower door test for homeowners who need a leakage measurement for a specific purpose — program compliance, post-work verification, or a baseline before undertaking improvements.
Contact usNew Construction Testing
Code-compliance blower door testing for new construction. We test to the IECC standard and provide documentation for the building permit. Retests available at $295 when the initial test fails or when verification of corrective work is needed.
Builder servicesReady to Know How Leaky Your Home Is?
Blower door testing is included in the Home Performance Assessment — the right starting point for any building-performance project.