So What Is a HERS Index?
If you are in the process of looking for a new home, or inquiring about energy efficient homes, you may have heard of a HERS Index. So what is a HERS Index anyway? Here is the definition taken form the RESNET website: “The HERS Index is a scoring system established by the Residential Energy Services Network (RESNET) in which a home built to the specifications of the HERS Reference Home (based on the 2006 International Energy Conservation Code) scores a HERS Index of 100, while a net zero energy home scores a HERS Index of 0. The lower a home’s HERS Index, the more energy efficient it is in comparison to the HERS Reference Home.
Each 1-point decrease in the HERS Index corresponds to a 1% reduction in energy consumption compared to the HERS Reference Home. Thus a home with a HERS Index of 85 is 15% more energy efficient than the HERS Reference Home and a home with a HERS Index of 80 is 20% more energy efficient.”
So essentially, when a HERS Rater evaluates a home, he or she will enter just about every aspect of the home into the software (Rem/Rate). The software will then model the actual house measured against a theoretical identical house, but this other house is built only to the current building code. The output is then the HERS Index, which will tell you how much more energy efficient the actual house is, compared to the same house, had it been built only to current code. The lower the score the better. This is a very useful tool in evaluating a particular home relative to the same home had the builder simply opted to build it to code. While this software is very sophisticated, there are so many nuances to the way a home and its occupants use energy that it’s virtually impossible to predict with any certainty the actual dollar amount of any bills. Currently, to earn an Energy Star Label a home must receive a HERS Index of 85, meaning, it must use 15% less energy than the same home built to code.
This is also a very effective tool for builders who build many of the same floor plans and want to model the impact of using various energy efficient upgrades to their houses. A HERS Rater can very easily and quickly evaluate the benefits of say, adding additional insulation to the attic, or changing the orientation of a building, or upgrading the windows. This allows a builder to quickly identify those upgrades which will have the greatest impact to their home.
As the HERS Index and Rem/Rate become more readily adopted by the industry and as we find more homes becoming energy efficient, look for more aggressive home performance targets from Energy Star. I think we’ll see some significant changes coming in the near future.
