A home’s airtightness is one of the most significant factors influencing its HERS Score. Air leakage increases heating and cooling loads, reduces comfort, and makes mechanical systems work harder—especially in New England’s cold climate.
Blower Door Testing quantifies this leakage and directly impacts the energy model used to determine your final HERS Rating.
How Air Leakage Affects Energy Efficiency
Uncontrolled air leakage allows conditioned air to escape and outdoor air to enter, increasing heating and cooling costs while creating drafts and uneven temperatures throughout the home. Over time, this air movement can introduce moisture into wall and ceiling assemblies, raising the risk of durability issues and mold. Excess leakage also forces HVAC systems to work harder, reducing efficiency and contributing to poor indoor air quality.
Explore details on blower door testing here: What Is a Blower Door Test?
Airtightness in the HERS Model
The HERS Index relies on blower door test results, measured as ACH50, to quantify how airtight a home’s envelope is under standardized conditions. This data is used to evaluate overall envelope performance, calculate heating and cooling loads, and determine required ventilation rates. Airtightness measurements also factor directly into projections of overall energy usage, making blower door testing a critical input for accurate HERS modeling and code compliance.
Learn how the rating is determined: Understanding Your HERS Score
Required Airtightness Levels in MA & RI
Massachusetts
- Base Code: ≤ 3 ACH50
- Stretch Code: ≤ 3 ACH50 (lower for high-performance homes)
Rhode Island
- RI IECC 2024: ≤ 3 ACH50
Learn more: Blower Door Testing for Code Compliance
Improving Airtightness Before Testing
Before blower door testing, Energy Geeks may recommend targeted improvements to reduce air leakage and improve overall performance. These measures can include sealing gaps around penetrations, adding or upgrading weatherstripping at exterior doors, and addressing common attic and basement bypasses. In some cases, improving insulation installation or completing duct sealing can further enhance airtightness and help ensure testing results accurately reflect the home’s intended efficiency.
Learn how preparation works: Test Preparation & What to Expect