How airtightness affects energy efficiency

Unsealed cracks and openings in a home's exterior—also known as the "building envelope"—can lead to significant energy loss.

Energy waste: Air leakage can account for 25% to 40% of the energy used for heating and cooling in a typical home. Conditioned air escapes through cracks, forcing HVAC systems to work harder and increasing utility costs.

Reduced comfort: Air leaks cause drafts and lead to uneven temperatures throughout the house, creating uncomfortable hot or cold spots.

Poor indoor air quality: An effective air barrier helps control the flow of air and prevents outdoor pollutants like dust, allergens, and humidity from entering the home. A tight home with proper mechanical ventilation offers better control over indoor air quality.

Moisture problems: In both hot and cold climates, air leaks can allow moisture to enter wall cavities, where it can condense and lead to structural damage, mold, and mildew.

A blower door pressure test is the standard diagnostic tool used to measure a home's airtightness, identify air leaks, and quantify how much energy is being lost.

How blower door testing works

A blower door is a diagnostic tool consisting of a powerful, variable-speed fan mounted within an adjustable frame and a flexible panel that temporarily seals an exterior doorway. 

1. Preparation: To perform the test, all exterior windows, doors, and intentional vents (like fireplace dampers) are closed. All interior doors are left open to allow air to move freely throughout the house.

2. Depressurization: The fan is turned on to pull air out of the house, which lowers the air pressure inside relative to the outside. This pressure difference forces outside air to rush in through every unsealed gap and crack in the building envelope.

3. Measurement: A pressure gauge called a manometer measures the pressure difference, and the calibrated fan measures the total airflow needed to maintain a constant pressure. This measurement is most often taken at a standard pressure of 50 Pascals (Pa), which simulates a 20 mph wind blowing on every side of the home at once.

4. Leak detection: While the test is running, technicians can use tools like infrared cameras, smoke pencils, or their own hands to pinpoint the exact location of air leaks.

5. Analysis: The results are used to calculate the home's airtightness, often expressed in "Air Changes per Hour at 50 Pascals" (ACH50). This metric indicates how many times the entire volume of air inside the house is exchanged with outside air in an hour under the test's pressurized conditions. 

Key metrics

• Air Changes per Hour (ACH): Calculated by multiplying the blower door's airflow measurement in cubic feet per minute (CFM) by 60 and then dividing by the home's total volume. For residential properties, the lower the ACH50 number, the more airtight and energy-efficient the home.

• Cubic Feet per Minute (CFM): This is the direct measurement of airflow through the fan during the test. A higher CFM number indicates a leakier home. 

After the test

Based on the blower door test results, an energy auditor can recommend targeted improvements to reduce air leakage and increase energy efficiency, such as: 

• Adding weatherstripping to doors and windows.

• Applying caulk or sealants around plumbing, wiring, and other penetrations.

• Installing new insulation in attics, walls, and crawl spaces. 

For new construction or very airtight homes, mechanical ventilation may be necessary to ensure adequate fresh air for a healthy indoor environment.