Many homeowners and home buyers are looking to home rating systems to ensure that their homes reach energy-efficiency targets and to potentially qualify for government rebates. 
Builders also support home rating systems as they provide a valuable selling point for prospective homeowners. One of these rating systems is the increasingly popular HERS index which has just been adopted as part of the 2015 International Energy Conservation Code (IECC).
What is a HERS Index?
The HERS Index measures the energy efficiency of a home. From the Residential Energy Services Network: “The Home Energy Rating System (HERS) Index is the industry standard by which a home’s energy efficiency is measured. It’s also the nationally recognized system for inspecting and calculating a home’s energy performance.”
The HERS Index indicates how much energy your home is using (or potential energy consumption) and where improvements could be made to increase efficiency. Older homes score about 130 on the HERS Index while a modern energy efficient home should score about 100. This score is based on specifications found in the 2004/2006 International Energy Conservation Code.
The 100 index is based on energy consumed by heating, cooling, lights, water heating and some appliances. Each 1% change in the HERS Index indicates a 1% change in energy efficiency with 0% being a net-zero home which produces as much energy as it consumes. Consequently; a home that score 70 will be 30% more energy efficient than a standard new home that scores 100.
How is HERS calculated?
Your home’s score is calculated by a certified HERS Rater who compiles energy usage data from the home and compares that data with the reference home with a score of 100 that has a similar size, shape and design in the same climate zone. According to RESNET: “The reference home is the geometric twin of the rated home, configured to a standard set of thermal performance characteristics, from which the energy budget, that is the basis for comparison, is derived.”
When you apply for a HERS Index rating, you get a number that shows how your home’s energy use compares to a reference point; that being the HERS Reference Home. The inclusion of the HERS Index in the 2015 Energy Code will encourage builders to construct more homes which adhere to a higher standard of energy efficiency and it highlights the need for an index which accounts for climate zone.