Founder | BPI® Energy Auditor Certified Professional
You might wonder how energy efficient your home is. One of the most accurate tests of energy efficiency is the HERS Index. So what is the HERS Index, and how does it work?
The HERS (Home Energy Rating System) Index is the national standard for inspecting and measuring a home’s energy performance. The HERS Index focuses on energy consumed in a home, identifies areas for improvement, and tracks energy progress.
In the rest of this post, I will answer your questions about the HERS Index, what it includes, and why it matters. Understanding HERS should be a critical part of your plan if you’re serious about energy efficiency.
What Is a HERS Rating?
A HERS rating measures a home’s energy efficiency.
Residential Energy Service Network (RESNET) developed the HERS rating and is the nationally recognized certifier.
The rating ranges from 0-150, with a higher score indicating a less energy-efficient home.
To calculate the HERS Index, RESNET compares a home’s energy consumption to a reference home, defined by a home built to the 2006 International Energy Conservation Code (IECC).
A house with a HERS Index of 100 is as energy efficient as the reference home.
The HERS rating is primarily used on newer homes with more options for new energy-efficient technology.
However, older houses can still receive a HERS rating, so the occupants should expect a higher score that indicates a less energy-efficient home.
What Is an Average HERS Score?
The average HERS rating is 100 for a new home. RESNET bases this average on a new home built to the IECC 2006 code.
Some states require a lower HERS score for new construction, such as California, which mandates a score of 55.
Resale homes perform much worse in the HERS test, with the average score being 130.
When comparing against the new home average of 100, the typical resale home is 30 percent less efficient than a new home built to the 2006 IECC code.
The average of a particular state can vary due to environmental, economic, and legislative issues.
The five states that had the best and worst scores in 2021 are showcased in this table.
| Lowest HERS Score | Highest HERS Score |
| California (33) | District of Columbia (81) |
| Vermont (38) | Tennessee (69) |
| Alaska (40) | Kansas (68) |
| Maine (41) | Arkansas (67) |
| South Dakota (43) | Alabama (66) |
The above report is a sample of a HERS rating calculation we did on our first netzero home renovation project. You can see that the -$72 per year actually means the home produces more energy than it uses, producing a very low HERS rating. It says Not Certified because we used it for testing and didn’t pay for the test to be done yet.
What Is a Good HERS Rating?
A HERS index of under 100 is more energy efficient than a typical home built in 2006, with a score of 0 equaling a net-zero energy home.
For example, a house with a rating of 80 is 20 percent more energy efficient than a standard new home.
On the other hand, a home with a rating of 120 is 20 percent less efficient than a new home built to the 2006 IECC.
According to RESNET, out of all homes inspected and rated in 2021, the average HERS rating was 58. This rating means that it was 42 percent more efficient than a house with a rating of 100.
Most resale houses have a rating of 130, meaning they are 30 percent less efficient than a typical home built in 2006.
What Does a HERS Test Consist of?
A certified HERS rater conducts a HERS test and typically follows these steps.
- Site inspection: The rater will visually inspect the home’s building envelope and check for proper insulation and air sealing.
- Testing of systems: The rater will test the efficiency of the home’s heating and cooling systems.
- Blower door test: The rater will use a blower door device to measure the air leakage in the home’s building envelope.
- Duct blaster test: The rater will use a duct blaster device to measure the air leakage in the home’s ductwork.
- Data collection: The rater will collect data from all tests and use specialized software to analyze the results. They will then compare the home’s performance to a reference home that meets the guidelines set by RESNET.
- Report generation: The rater will produce a report that includes the home’s HERS rating, energy consumption, and recommendations for improvements to increase the home’s energy efficiency.
You may not know what a blower door test is, so here is a helpful guide.
When Is a HERS Test Required?
A HERS test is not typically required by law, but it can be beneficial for several reasons.
● To comply with local or state energy codes
● Incentive programs for energy-efficient homes
● Mortgage lenders may require a HERS test as part of the underwriting process to estimate utility bills and ensure the house is energy-efficient
● Homeowners may conduct a test to assess and increase the home’s energy efficiency
How Long Does a HERS Test Take?
The length of a HERS test can take between two and four hours, depending on the size and complexity of the home.
Specific variables will make a HERS test longer depending on the climate zone and the house’s location.
To get an accurate HERS rating from RESNET, the homeowner must use a certified HERS rater for the inspection.
What Does a Negative HERS Rating Mean?
A negative HERS rating means that a home produces more energy than it consumes and has an energy surplus. The homeowner can use the excess energy to power the house or sell it back to the grid.
You can also apply for special government incentives if your home has a negative rating.
To attain a negative HERS rating requires substantial financial investment into renewable energy and sustainable technology.
Furthermore, there can be many costs of renovation to build the necessary infrastructure needed to achieve a negative HERS rating.
Is My Property More Valuable with a Negative HERS Rating?
A negative HERS rating can make it more attractive to potential buyers. Energy savings, environmental benefits, and the ability to produce energy are benefits that can increase property value.
Of course, many other market factors can affect property value. Still, a negative HERS rating could entice a specific environmentally-conscious buyer.
Source: A9 Green HERS Index
How Do I Lower My HERS Score?
Decreasing energy consumption will reduce a home’s HERS rating. There are several things you can try to lower your rating:
- Add insulation and check air sealing
- Install windows
- Upgrade HVAC systems
- Change lighting
- Install solar panels
- Replace the water heater
This guide on water heaters is very valuable for understanding your heat consumption.
Final Thoughts
Knowing your rating on the HERS Index will help you analyze how much energy your home consumes.
An average new home will score 100, but many energy-efficient new homes will score much lower than the average. A negative HERS is possible for a home that produces more energy than it consumes.
A certified HERS rater must perform the test, which usually takes two to four hours to complete.
Some options to lower a HERS score include installing solar panels, upgrading your HVAC system, or installing LED light fixtures.