Why a Tight Blower Door Score Is Critical to HERS Success in 2025 Massachusetts Homes
Overview
Airtightness isn’t just a checkbox—it’s one of the biggest drivers of energy performance in new homes. In Massachusetts, where the Stretch Code requires 3 ACH50 or less, your blower door test result can make or break your HERS (Home Energy Rating System) score.
In this article, we’ll explain what a blower door test measures, how it impacts HERS modeling, and why proper air sealing during construction is essential. If you’re building a new single-family home in 2025, these insights could mean the difference between code compliance and costly delays.
What Is a Blower Door Test?
A blower door test measures how much air leaks through a home's envelope by depressurizing the house and quantifying how quickly air enters through gaps and cracks. The result is expressed in Air Changes per Hour at 50 Pascals (ACH50).
Why Airtightness Matters
Air that leaks into a home often brings unconditioned outdoor air, which increases heating and cooling demand.
Leaky homes are harder to make comfortable.
ACH50 scores directly affect a home’s HERS rating—lower leakage typically means a lower (better) score.
Stretch Code Requirements
As of 2025, Massachusetts homes built in Stretch Code municipalities must achieve 3 ACH50 or better. That’s a tight standard, and it emphasizes the importance of continuous air barriers, detailed planning, and quality installation.
How the Blower Door Score Impacts HERS Ratings
In a HERS model, blower door results are one of the most influential performance variables. Here’s why:
Every point counts: A poor test result (e.g., 5 ACH50 instead of 2.5 ACH50) can raise your HERS Index by 5–8 points—potentially causing a failure in Stretch Code towns.
Other systems get dragged down: Even if you have high R-values and an efficient heat pump, excessive leakage can offset those gains.
Tighter homes often qualify for increased incentives: Lower HERS scores can unlock greater rebates, especially for all-electric or solar-integrated homes.
How to Achieve ≤ 3 ACH50 Without Guesswork
Massachusetts builders aiming to hit or exceed the 3 ACH50 blower door requirement should treat airtightness as a design priority, not an afterthought. That means thinking about air control from the first site meeting through final inspection.
Begin With the Barrier
Every build should start with a clearly defined air control layer. For most new construction in 2025, the best results come from exterior air barriers—such as taped sheathing, fluid-applied membranes, or fully adhered housewraps. These systems are easier to inspect, less prone to being compromised by subs, and generally outperform interior approaches like airtight drywall.
Be Strategic About Penetrations
Mechanical chases, hose bibs, can lights, and bath fans often turn into leak factories if not detailed properly. Take the time to walk the framing and layout before trades arrive, and make sure every penetration is sealed with durable materials like acoustical sealant, backer rod, or tape systems designed for air sealing.
Don’t Skip Early Testing
One of the smartest things builders can do is schedule a mid-construction blower door test—usually after sheathing and rough-ins but before insulation. This is your chance to find and fix leaks while they’re still accessible. Catching a framing gap or attic bypass at this stage can save you hours of finish work down the line—and could improve your HERS score by several points.
Watch the Usual Suspects
Even tight homes can fail blower door tests due to overlooked problem areas. Pay close attention to:
Attic transitions (especially at top plates)
Basement rim joists and sill plates
Garage-to-house connections
Chases and dropped soffits
These areas often get rushed—and they’re some of the biggest contributors to leakage.
Remember: air sealing isn’t just about meeting code—it’s about delivering a better, more comfortable home that performs well for decades.
Common Questions
What happens if I fail the blower door test?
If your home doesn’t meet the required 3 ACH50 or lower, you won’t be able to finalize your HERS Rating or meet code in a Stretch Code town. In most cases, this means bringing in additional air sealing measures—such as AeroBarrier—to tighten up the envelope.
While it’s rarely necessary to open up walls, addressing the issue after insulation and drywall can be more labor-intensive and costly than if it’s caught earlier. That’s why we recommend mid-construction testing to catch leaks when they’re easiest to fix.
Is there a benefit to going tighter than 3 ACH50?
Yes. Tighter homes are more comfortable, require smaller HVAC systems, and achieve better HERS scores—often unlocking rebates.
What’s the easiest way to improve my ACH50?
Start with framing-stage air sealing. Once insulation is in, your options are limited and more costly.
Can Spectrum Energy help?
Absolutely. We offer HERS ratings, mid-construction blower door testing, and actionable guidance to make sure you hit your targets the first time.
Planning a new construction project in 2025? Let Spectrum Energy help you design and build for airtightness and HERS success. Contact us today to schedule your blower door test and energy rating consultation.
