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What is the HERS Index?

The HERS Index is a numerical scale that provides a standardized means of comparing the energy consumption of two or more homes. In order for a home to be issued a HERS Index score; an assessment must be performed by a certified rater. Raters apply the data collected from the assessment process into industry accredited software. The software generates a virtual reference home with similar characteristics as the assessed home. The reference home however, is modeled to comply with but not exceed the minimal energy code requirements.

The software performs a comparison between the assessed home and the reference home. The reference home’s minimal compliance achieves a numerical HERS Index score of 100. If the assessed home performs more efficiently, the increased performance is reflected by a reduction in its HERS Index score. Each 1-point reduction in its HERS Index score reflects a 1% reduction in energy consumption. A self-sufficient home that generates all of its own energy has a HERS Index score of 0.

For a new to-be-built home the rating process involves the review of the building plans by a RESNET certified rater prior to home construction. A projected HERS Index score is estimated based on the plan specifications. The rater works with the builder throughout the construction process providing recommendations that will increase the homes performance. A confirmed rating is performed upon completion of the home. For existing homes, on-site diagnostic testing and data collection are performed. The results are entered into the accredited software, a reference home is generated for comparison, and a HERS Index score is obtained.

The recommended improvements can be entered into the software in order to display resulting effects.

The HERS Index of Reference Home is always 100.
Reference Home always = 100,
Assume the Evaluated Home = 65,

This means the evaluated home is 35% more efficient than the reference home that is modeled to meet minimal code.  The Hers Index Of the assessed home reflects the % more efficient or less efficient than the reference home. A HERS Index of 85 or lower earns the ENERGY STAR label.