A home energy rating involves an analysis of a home's construction plans or an onsite inspection. The Home Energy Rater uses an energy efficiency software package to perform an energy analysis of the home's design. This analysis yields a projected, pre-construction HERS Index.

Upon completion of the plan or site  review, the rater will work with the builder or home owner to identify the energy efficiency improvements needed to reduce the HERS Index or to ensure the house will meet certain program guidelines such as ENERGY STAR which are separate from the HERS rating. The rater conducts onsite inspections, typically including a blower door test (to test the leakiness of the house) and a duct test (to test the leakiness of the ducts). Results of these tests, along with inputs derived from the plan or site review, are used to generate the HERS Index for the home.

Unlike a Building Performance Audit or a weatherization assessment, a home energy rating is a recognized tool in the mortgage industry. Home energy ratings can be used in a variety of ways in the housing industry. Since a rating quantifies the energy performance of a home, the HERS Index provides an easily understandable means to compare the relative energy efficiency of different homes.

The HERS Index

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 2004 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 score, the more energy efficient it is in comparison to the HERS Reference Home.