Home >Articles >Florida Solar Energy Center Publishes Study “Relationship between the U.S. Department of Energy’s Home Energy Score (HES) and RESNET’s Home Energy Rating System (HERS)”

Florida Solar Energy Center Publishes Study “Relationship between the U.S. Department of Energy’s Home Energy Score (HES) and RESNET’s Home Energy Rating System (HERS)”

Feb 25, 2016

The U.S. Department of Energy (DOE) has developed the Home Energy Score (HES) energy performance labeling program.   According to Kathleen Hogan, DOE’s Deputy Assistant Secretary for Energy Efficiency and Renewable Energy, DOE developed HES as “an easy-to-use, low-cost reliable and motivational tool” for existing homes.  As such, it is a valuable tool for existing homes. Since the program was developed, it has been promoted as a home energy rating program and as a proposed substitute for HERS in FHA energy efficient mortgages and an IECC code compliance option.

To explore the usefulness of HES in these applications, the Florida Solar Energy Center has published a study that investigates if there is a reasonable correlation between the HES and the HERS Index and if there is a reasonable correlation between HES and IECC code compliance.

The principle findings from the study clearly show that there is a fundamental difference between HES and HERS – HES is a measure of home energy use while HERS is a measure of home energy efficiency and relative performance. HES does not account for home size, the number of home occupants or energy use for lighting and appliances. As a result, there is no useful correlation between HES and current building energy codes or high-performance home programs like EPA’s ENERGY STAR homes program or DOE’s Zero Energy Ready Homes program, all of which focus on home energy efficiency and relative energy performance rather than absolute energy consumption. Because the HES methodology focuses on home energy use without consideration of home energy efficiency, larger homes of the same energy efficiency achieve substantially poorer HES score results than do smaller homes. The tool used for HES can produce accurate estimates of energy use but it cannot be used as a metric of home energy efficiency in the context of the current and longstanding methodology of energy efficiency determination for code compliance.

The main findings of the study are:

  • There is no statistically useful relationship between HES and compliance with any level of IECC code.  In order to make it compliant it would require a fundamental altering of how the IECC is structured.
  • There is no evidence of any correlation between HES and HERS Index scores.  There is a strong statistical correlation between HERS and IECC code compliance.
  • HES, which is based on an absolute source energy use scale, is not able to reasonably represent either current energy code compliance or ENERGY STAR certification
  • Results from parametric simulation analysis indicate that the source energy use bins used for HES scoring may be flawed for certain weather locations

The above findings suggest that HES is not an appropriate tool for the energy rating of new homes for energy code compliance or ENERGY STAR Home certification.  For HES to be useful, the entire philosophy, and subsequent methodology, for setting energy codes would need to be transformed to reflect the home size issue.

To download the study go to Relationship between the U.S. Department of Energy’s Home Energy Score (HES) and RESNET’s Home Energy Rating System (HERS)

The 2016 RESNET Building Performance Conference will be offering the session “All Things Are Not Equal – Comparing the RESNET HERS Index and the U.S. Department of Energy Home Energy Score”.  The session is led by the co-authors of the study, Philip Fairey of the Florida Solar Energy and Brett Dillon of the Dillon Group.  For more information go to 2016 RESNET Building Performance Conference