Energy efficiency isn’t just about comfort or lower bills—it’s about quantifying performance. The Home Energy Rating System (HERS) provides that benchmark, allowing homeowners, builders, and energy auditors to measure how efficiently a property operates.
At Home Energy Efficiency Consultant, we specialise in performing HERS testing across Massachusetts to help homeowners understand their home’s true efficiency level. This article explains how the HERS Index works, how scores are calculated, and the key tests involved in the process.
HERS Index Overview
The HERS Index is the nationally recognised scoring system developed by RESNET (Residential Energy Services Network). It measures a home’s energy performance and provides a single number to represent how efficiently it consumes and conserves energy.
Every home’s rating is benchmarked against a reference home—a theoretical model built to 2006 International Energy Conservation Code (IECC) standards. A HERS score of 100 represents that benchmark. Scores below 100 mean the home is more efficient; scores above 100 indicate it uses more energy than a standard new home.
Interpreting the HERS Rating Scale
The HERS Index scale ranges from 0 to 150, where:
- 0 represents a net-zero energy home—a property that produces as much energy as it consumes.
- 100 indicates a code-built home with standard energy performance.
- Every point above or below 100 corresponds to approximately 1% more or less energy use compared to the reference home.
Typical homes in Massachusetts generally fall between 60 and 90, depending on their age, insulation quality, heating system efficiency, and construction methods.
A score of 60 means the home is about 40% more efficient than a standard new build, while a score of 130 means it consumes 30% more energy than the baseline.
Step-by-Step Breakdown of the HERS Testing Process
To generate an accurate HERS Index score, a certified RESNET Home Energy Rater performs a combination of on-site testing and energy modeling. These procedures assess air tightness, ductwork leakage, insulation effectiveness, and mechanical system efficiency.
Blower Door Test for Air Tightness
The blower door test measures how airtight a home is—a critical factor influencing heating and cooling efficiency.
A high-powered fan is temporarily installed in an exterior doorway. When the fan depressurises the home, it forces air through unsealed gaps, cracks, and penetrations. Sensors then measure the air leakage rate, expressed in CFM50 (cubic feet per minute at 50 Pascals).
- High CFM50 readings indicate significant air leakage, meaning more conditioned air escapes and outdoor air enters.
- Low CFM50 readings show good air sealing and higher efficiency.
This test helps pinpoint energy loss through walls, ceilings, attics, and foundation gaps. Improving air tightness often yields some of the highest energy savings per dollar spent.
Duct Leakage Test for Air Distribution Efficiency
The duct leakage test evaluates the efficiency of the home’s HVAC distribution system. Even well-sealed homes can lose substantial energy through leaky ducts that allow conditioned air to escape before it reaches living spaces.
During testing, a duct blaster fan is connected to the home’s HVAC system. All supply and return vents are sealed, and pressure measurements are taken to determine leakage levels. The results are expressed as a percentage of system airflow lost through leaks.
For example:
- Tight duct systems may lose less than 4% of air.
- Older or poorly sealed systems can lose 20–30% or more, significantly impacting comfort and energy use.
Addressing duct leakage not only improves efficiency but also enhances indoor air quality and system longevity.
Energy Modeling and Data Analysis
After completing physical testing, the energy rater gathers detailed information about the home’s structure and systems, including:
- Wall, roof, and floor insulation R-values
- Window and door specifications
- HVAC equipment type, capacity, and efficiency
- Water heating system and ventilation details
- Lighting and appliance efficiency
All data is entered into RESNET-approved energy modeling software that simulates the home’s annual energy consumption under standard conditions.
The model compares the tested home to the reference model to generate the final HERS Index score. This score provides a direct, numerical indicator of the home’s overall energy performance.
Learn More: Step-by-Step Guide to Getting Your Home HERS Rated in Massachusetts
Interpreting HERS Scores in Real-World Terms
A HERS Index score doesn’t just represent efficiency—it directly correlates with energy costs and environmental impact.
Below is a general guide to interpreting HERS scores:
| HERS Score | Energy Efficiency Level | Approximate Energy Use Compared to Standard Home | Typical Example |
| 0 | Net-zero | 0% | Produces as much energy as it uses |
| 40–60 | High efficiency | 40–60% less | ENERGY STAR® homes or high-performance builds |
| 70–90 | Moderate efficiency | 10–30% less | Typical modern homes in Massachusetts |
| 100 | Standard code-built | Baseline | 2006 IECC reference home |
| 130+ | Low efficiency | 30% more or higher | Older, unretrofitted homes |
A lower score not only means reduced energy bills but often increased resale value, as energy-efficient homes are increasingly desirable to buyers in the Massachusetts housing market.
Key Factors That Influence the HERS Index
Several design and construction elements contribute to a home’s HERS rating. Understanding these allows homeowners and builders to target improvements strategically.
Building Envelope Quality
Insulation, air sealing, and construction materials have a direct impact on how well a home maintains indoor temperatures. Poor insulation or air leaks in attics, walls, and basements are major contributors to higher HERS scores.
HVAC System Performance
Outdated or improperly sized HVAC units consume more energy than necessary. High-efficiency heat pumps, sealed ductwork, and smart thermostats can dramatically lower a home’s HERS score.
Window and Door Efficiency
Low-E coatings, proper installation, and energy-rated windows prevent heat loss in winter and reduce cooling demand in summer—both critical in Massachusetts’ variable climate.
Lighting and Appliances
ENERGY STAR-certified lighting, appliances, and water heating systems contribute to a lower HERS score by reducing overall energy consumption.
Renewable Energy Integration
Incorporating solar panels or other renewable systems can offset the home’s total energy use, helping reach a HERS score closer to zero.
Benefits of Knowing Your HERS Rating
Understanding your HERS Index is more than an academic exercise—it’s a roadmap for improving performance and controlling energy costs.
Homeowners who invest in efficiency upgrades based on their HERS report typically experience:
- Lower monthly utility bills
- Improved indoor comfort and air quality
- Increased property value
- Eligibility for rebates and incentives through Massachusetts Clean Energy Center and Mass Save programs
- Reduced carbon footprint through decreased energy consumption
For builders, achieving a lower HERS score can also improve compliance with local building codes and help qualify for certifications like ENERGY STAR, LEED for Homes, or Zero Energy Ready Home.
Learn More: How Energy-Efficient Upgrades Impact Your HERS Score in MA
HERS Ratings in the Massachusetts Context
Massachusetts has some of the most ambitious energy efficiency standards in the United States. Many towns require HERS testing for new construction or major renovations as part of their Stretch Energy Code compliance.
Typical new homes that meet Massachusetts code today average around HERS 55–65, while high-performance or Passive House designs can achieve scores under HERS 40.
Older properties, especially those built before modern energy codes, often exceed HERS 100, highlighting the need for weatherisation, improved insulation, and HVAC upgrades.
Final Perspective
The HERS Rating serves as a precise, data-driven benchmark for understanding a home’s energy performance. It combines scientific testing, modeling, and measurable metrics to guide homeowners toward smarter energy decisions.
For Massachusetts homeowners aiming to reduce costs, improve comfort, and enhance sustainability, getting a professional HERS test is the most effective first step.Learn more about our comprehensive testing and reporting services on our HERS Rating Massachusetts page — or contact Home Energy Efficiency Consultant to schedule a consultation with a certified rater.
