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What is a HERS rating?

A home energy rating (HERS) is an analysis of a home's projected energy efficiency in comparison to a 'reference home' based on the 2006 International Energy Conservation Code. A home energy rating involves both an analysis of a home’s construction plans, as well as onsite inspections and testing by a certified Home Energy Rater.

A Home Energy Rater uses specially-designed software to analyze the expected energy use of the home based on the home’s construction plans. This analysis yields a projected, pre-construction rating score for this home (called a HERS Index). When the rating is being conducted for the purposes of qualifying the home to the earn the ENERGY STAR, the rater then works with the builder to identify the energy efficiency improvements needed to ensure the house will meet ENERGY STAR performance guidelines.

The rater then conducts onsite inspections, typically including a blower door test to determine the leakiness of the house.  A blower door is a variable speed fan, mounted in a doorframe, used to pressurize and depressurize a house to measure air leakage.  The HERS rater is trained to use this equipment and analyze the data read-outs.  If your home has ducts, the rater will perform a duct blaster test to test the leakiness of the ducts.  A duct blower is a variable speed fan that is attached to a duct system to measure duct air leakage.  The equipment measures the pressure relative to the outside and inside air pressure. Results of these tests, along with data from the software analysis, are used to generate a final HERS Index score for the home.

The lower a home’s HERS Index, the more energy efficient it is. A home built to code scores a HERS Index of 100, while a net zero energy home scores a HERS Index of 0. 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 reference home and a home with a HERS Index of 80 is 20% more energy efficient.

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