When it comes to buying or building a home, energy efficiency is more important than ever. Almost all homebuyers look at the price of the home, the mortgage interest rates and the taxes on the home. But, determining how energy-efficient one home is compared to the next can save you money in the long run. Rising utility costs and growing environmental awareness have made energy-efficient homes a smart and sustainable choice. But not all energy-efficient homes are equal. That’s where the HERS Index comes in. Short for Home Energy Rating System, the HERS Index is the nationally recognized scoring system for measuring a home’s energy performance.
What Is a HERS Rating?
Think of a HERS Rating like a miles-per-gallon sticker, but for houses. Developed by RESNET (Residential Energy Services Network), the HERS Index tells you how energy-efficient a home is compared to a standard new home. The lower the score, the better the energy performance.
HERS Rating: The Measurement Tool
The HERS Index is a numerical score that measures a home’s energy performance. It's like getting a test score for how efficient the home is. A lower score means better efficiency.
For example:
- A HERS score of 100 = standard new home (baseline).
- A HERS score of 70 = 30% more energy-efficient than the baseline.
- A HERS score of 0 = net-zero home.
Most older homes score between 130 and 150, while energy-efficient new homes often score below 70.
What’s Involved in a HERS Rating?
A HERS Rating is determined after a certified HERS Rater performs a series of tests and inspections to assess the home’s energy efficiency. These include:
Blower Door Test
A blower door test is a diagnostic tool used to measure how airtight a home is. It helps identify air leaks, which are areas where warm or cool air escapes. These leaks can waste energy, raise utility bills, and make a home less comfortable.
Duct Leakage Test
A duct leakage test is used to measure how much air escapes from a home’s heating and cooling ductwork. When ducts have leaks, conditioned air can escape into unconditioned spaces like attics, crawlspaces, or walls, making your HVAC system work harder and driving up energy costs.
Insulation Inspection
An insulation inspection looks for the appropriate insulation for the climate and ensures it is placed where it should be (walls, attic, crawlspace.) It looks at the quality of the installation to determine if there are gaps, compression, or missing areas. Poor installation can significantly reduce performance. And last, it looks at the R-value to determine if the insulation meets or exceeds the recommended R-value (a measure of thermal resistance) for the area?
Windows Inspection
In the windows inspection the Rater looks at the U-factor (how well the window insulates) and Solar Heat Gain Coefficient (how much solar heat the window lets in). It looks at Air leakage to determine if the windows are properly sealed and caulked to prevent drafts. And it looks at the Frame and glass type to determine if the windows are double- or triple-pane and if they are ENERGY STAR® rated?
Ventilation Inspection
In the ventilation inspection, the Rater looks at mechanical ventilation to determine if the home has a Heat Recovery Ventilator or Energy Recovery Ventilator to bring in fresh air and expel stale air. It looks at the bathroom and kitchen fans to ensure they are properly vented to the outside and function efficiently. And it also looks at the airflow balance to ensure the ventilation system maintains a healthy indoor air quality without wasting energy.
Inspection of Appliances
Next, the Rater looks at the age, efficiency and Energy ratings of the installed appliances looking to see if they are ENERGY STAR certified. Older appliances typically use more energy than newer ones. The rater will also look at the type of appliance and fuel source. For instance, an electric vs. gas range or electric vs gas dryer. Efficient models lower energy consumption and improve the HERS score.
Evaluation of solar panels, if present
If the home has solar panels installed, the HERS Rater will look at the system size, orientation, tilt, and efficiency to determine how much renewable energy the home produces. This helps offset the home's total energy use and can significantly lower the HERS score.
After testing is completed, the rater enters all the data into software and a HERS Index Score is calculated.
Why Does the HERS Index Score Matter?
The HERS Index score matters because a lower HERS score translates to lower energy bills, improved comfort, and reduced environmental impact. For homeowners, this means monthly savings and better air quality inside the home. For home buyers, a low HERS score can signal a well-built, future-proof investment.
Builders often use HERS Ratings as a selling point, demonstrating the home's efficiency and quality. In fact, some mortgage lenders now consider a home’s HERS Rating when evaluating a buyer’s loan eligibility since lower utility bills reduce monthly expenses.
Is a HERS Rating and ENERGY STAR® the Same Thing?
A HERS Rating and ENERGY STAR® certification are closely related, but they aren’t the same thing. Here's how they connect:
ENERGY STAR®: The Certification
ENERGY STAR® is a label given to homes that meet specific energy efficiency standards set by the U.S. Environmental Protection Agency (EPA). These standards are stricter than typical building codes and include:
- Efficient heating and cooling systems
- High-performance windows
- Proper insulation and air sealing
- Verified energy-efficient lighting and appliances
To qualify, a home must be independently verified—and this is where the HERS Rating comes in.
How They Work Together
To earn the ENERGY STAR label, a home must be rated by a certified HERS Rater. The rater uses HERS Index testing (blower door, duct leakage, insulation inspection, etc.) to determine if the home meets ENERGY STAR program requirements.
While there isn’t a single required HERS score to earn ENERGY STAR, homes usually need to score around 70 or lower, depending on the climate zone and ENERGY STAR version.
So in simple terms:
- HERS is the score.
- ENERGY STAR is the badge.
- You can have a HERS Rating without ENERGY STAR, but not the other way around.
If you're buying or building a home and it has both a low HERS score and an ENERGY STAR label, it means:
- You’re getting a home that’s built better.
- You will pay less in utility bills.
- You’re reducing your environmental impact.
It’s a win-win for your wallet and the planet.