HERS (Home Energy Rating System) Index

The above scale is called the HERS Index. This Home Energy Rating Systems Index is a useful tool for comparing the energy efficiency of different homes, although it is not without its shortcomings.

What is the HERS Index?

The HERS Index was created by the Residential Energy Services Network (RESNET). As RESNET's website explains, the HERS Index is a scoring system in which a home built to the specifications of the HERS Reference Home (based on the 2004 International Energy Conservation Code) scores a HERS Index of 100, while a zero net energy home scores a HERS Index of 0. The lower a home's score, 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 the 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.

At Austin Design, in recent years we have designed and built homes ranging from a HERS Index of 53 to a HERS Index of 8. In other words, these homes are 47% - 92% more energy efficient than the HERS Reference Home (or, a standard home built to code, which is the same thing).

Why is the HERS Index controversial?

The link below offers an interesting forum discussion on the pro's and con's of the HERS Index:

http://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/14558/problems-hers-rating-system

Among the chief complaints of those pointing out the weaknesses of the HERS Index are that it does not take occupant behavior into account (which can dramatically affect the energy usage of a home).

Another issue arises with the accuracy of the software used to generate the HERS Index of a home. At least one of the two accredited software tools used to generate a HERS Index lacks data input to account for differences in the geometric shapes of two homes being compared. As folks know, a simply-designed home with fewer corners and less exterior surface area will perform better energy-wise than a home of relatively equal size and square footage that has a more complicated design with a greater number of corners and greater exterior surface area.

We enjoyed reading the above discussion and hope you will find it interesting too.