The HERS Index is THE Home Energy Efficiency Gauge

Serenbe Lane HERS Index Proud Green Home LG Squared, Inc.GET ON BOARD THE HERS TRAIN, YOU’LL BE GLAD YOU DID.

The HERS Index is already the industry standard for measuring a home’s energy efficiency. In 2015, the International Energy Conservation Code (IECC) will allow the option for all new homes to use the HERS Index to comply. Considering that residential buildings account for approximately 36.5% (2012 figures) of the electricity consumption in the United States, it’s a good idea to pay more attention to how homes are designed and built, and how we live in those homes. The HERS Index, while not perfect (what is?), is for both new construction and remodeling, and it’s primarily used to help ensure that a house and it’s occupants are on the right path to using lower energy consumption.

Most homeowners have never heard of it despite many builders making it standard in every home they build. Architects are somewhere between homeowners and builders. Property appraisers and Real Estate Professionals are starting to see the HERS Index show up in MLS listings, but are mostly unaware of what it means. Mortgage lenders are seeing it in applications for Energy Efficient  and Energy Improvement Mortgages (EEM and EIM), and almost every Green Building Certification in the U.S. requires it.


The HERS Index (Home Energy Rating System) is the calculated result of an in-depth audit, or HERS Rating, of an existing or proposed new home that includes evaluation, performance testing, and reporting of the proposed work scope. It’s baseline is set at 100, which represents the home as if it exactly meets the minimum requirements of the 2006 IECC. Every index point lower than 100 means the home is that much more efficient. For example, a home that earns a HERS Index of 77 (for everywhere EXCEPT California) means that it is 23% more efficient.

The index is determined by a certified HERS Rater, whom performs a HERS rating (some call it an energy audit) on the home. The rating includes diagnostic testing (air leakage in the home (blower door test) and it’s duct system (duct tester)), visual inspections, and energy modeling. The results estimate how the home compares to the same home built to the meet the 2006 IECC, and gives projections on the energy consumption of the home. Based on the utility rates, the rater’s proprietary software (REM/Rate, Energy Gauge or EnergyPro) generates anticipated energy consumption, heating/cooling loads, and energy costs based on the construction, mechanical systems and location of the home. The rater and his/her software can also perform cost benefit analyses to determine cost effective solutions to design and build efficiently.


Proud Green Home at Serenbe, LG Squared, Inc. HERS Index

The recently completed Serenbe Lane Residence, a.k.a. Proud Green Home, achieved a HERS Index of -2. The HERS Index scale at the beginning of this post is from the official HERS Rating we completed on the home. That -2 means it is 102% more efficient than if it had been built to exactly meet the 2006 energy code. It also means that the home should produce more energy than it consumes, because “0” is considered “net-zero”. Attention to details, good design, and often installing an on-site alternative energy source like photovoltaics or wind powered generators were what really drove the low index. Though I’d love to see every home reach this level of performance, not everyone is ready. That said, we have several homeowner clients seeking at least 50% better than code (i.e. HERS Index = 50 or lower). In fact, our Athens, Georgia client is asking us to design their home to out-perform the Serenbe Lane Residence. Game on!

proud green home serenbe lot 200 lg squared inc ribbon cutting (1)


This past week, Georgia Power Company hosted about 40 industry professionals (mostly HERS Raters) in Savannah, Georgia, for their annual EarthCents New Home Rater Conference. They presented updates to the Earthcents New Home Program, and shared the results of some interesting market research and campaigning they’ve done over the last year to increase awareness of the HERS Index and home energy efficiency.

As of January 1, 2014 (which is an improvement from 2013), builders building homes served by Georgia Power are being offered the following incentives:

Builder incentives available for each all-electric system listed:

  • Electric heat pump (standard efficiency < 15 SEER) – $250 per system* (where available; please contact your local Georgia Power representative for availability, confirmation and details)
  • High-efficiency electric heat pump ( > 15 SEER) – $100 per system
  • Heat pump water heater or solar water heater – $250 per system

EarthCents New Home (HERS-rated home) – A whole-house approach to energy efficiency. The home must be tested and verified utilizing the national standard HERS Rating Index to validate the energy savings.

  • Builder incentive – $600* per single-family home
  • Energy efficiency bonus incentive – $25 per point below 77 on the HERS Index

If the Serenbe Lane Residence had been served by Georgia Power, the Imery Group (builder) would have been eligible for a $2,900.00 rebate! $1,950.00 of that would have been from achieving a HERS Index of -2.


In some of their research, Georgia Power Company (GPC) discovered that about 75% of the homeowners in their focus group indicated that energy efficiency is a factor in the purchase of their home, and that a few builders had actually been asked by a homeowner about the HERS Index.

GPC has also undertaken a concerted public education campaign on the HERS Index in their service area.  The campaign includes radio ads, newspaper ads and billboards in the major urban areas of the state, as well as these two interesting videos that can be seen on their website:


Designing and building more durable and energy efficient homes is happening. Don’t get left behind!


Written by Chris Laumer-Giddens


12 Responses so far.

  1. We use the HERS index, if I think it is warm or cold we change something. 🙂

  2. Good to know, I had not heard about this, tks!!

  3. Martin Holladay says:

    This sentence is meaningless: “That -2 means it is 102% more efficient than if it had been built to exactly meet the 2006 energy code.”

    If you are comparing the energy use of X with Y, it’s best to say “Y uses 74% less energy than X.” If you say, Y is 74% more efficient than X, the meaning is much less clear.

    And I’m not really sure if even a physicist could properly explain what you mean when Y is 102% more efficient than X.

  4. Sabine Lam says:

    Why is the baseline in California higher than the rest of the US? I was under the impression that CA was more energy conscious and didn’t have to deal with extreme temperatures, which should result in a lower index?!

  5. I’ve heard of that one, Lisa! It’s being adopted by households all over the U.S. and Canada.

  6. Hi Sabine,

    Yes, all of that is generally true about California. They are one of the more progressive states in the country in terms of energy conservation.

    Extreme temperatures are not the only thing that affect energy consumption. In fact, lighting and appliances typically consume most of the energy in a home. In the case of the Serenbe house referenced in this post, lights and appliances are projected to consume approximately 43% of the total.

    However, neither lighting and appliances nor extreme temperatures lead California to have a HERS Index scale of 0-250. It’s just their that their scale extends to 250, where the National HERS Index actually stops at 150. And, that’s just the graphic that each uses. A HERS Index of 100 means the same thing in California as it does nationally…the house meets code. Anything above 100 is worse than code.

    I also would like to clarify that the baseline for California is also 100, and that 250 refers to the upper (or in terms of efficiency, “lower”) end of their HERS Index graphic scale. Nationally the graphic scale shows 150, as is shown in this post.

    The biggest difference between California and National HERS Indices is the baseline code. In California, their baseline code is California’s “2008 Building Energy Efficiency Standards”, and nationally it’s the “2006 IECC”. In general, the California code is more strict. It’s also more specific to California climate.

    Here is how California HERS Index scale is broken down.

    • “250” or more is likely to have very high energy bills, and many opportunities for efficiency improvements.
    • “100” uses the same energy as a new home that meets California’s 2008 Building Energy Efficiency Standards.
    • “0” is a super-efficient “Net Zero Energy Home” that consumes no more energy than it produces with solar or
    other onsite renewable sources.

    If you’re interested in more information about the California HERS Index, check out this document:

  7. Martin,

    Saying “more efficient” simplifies what I could have said in more detail, and that perhaps a physicist could explain. Since you bring it up, I am happy to explain what 102% more efficient means for this home.

    It is projected to use 61% less energy than if the home had been built to meet the requirements of the 2006 IECC. To provide enough power for the other 39%, the house is equipped with 10kw of on-site (roof) solar power. The remaining 2% (61+39+2 = 102) is excess power produced by the solar panels that is either sold back to the power company, used as a credit toward the next energy bill, or just extra.

    Saying “more efficient” is a common and simple way of explaining all this, which I believe we need more of. In fact, I know at least one self-proclaimed energy nerd who has used the same expression to explain how the HERS Index works in one of his own blog posts, saying, “The lower a home’s HERS Index, the more efficient the home.” It makes sense to more people, and in fact, has a lot of meaning.

    For our more technically-minded clients (we have several), I typically give more detail.

  8. […] Many cities and states across the country are starting to require some level of HERS ratings.  South Hampton NY is reported to require a HERS rating of 70 with larger homes have to be 50 or less.  Colorado is publishing HERS ratings in the MLS listings.  Read more in this descriptive article to learn more about HERS ratings:  The HERS Index is THE Home Energy Efficiency Gauge. […]

  9. […] to 50% better if he had been able to use double-pane windows. As it stands, the home should score a HERS rating of 65 to 75, he […]

  10. […] live there. Before the photovoltaic panels were considered for the home, it was rated, using the HERS Index, to use more than 60% less energy than if the home were designed and built to meet the minimum […]

Leave a Reply