Starting with the 2012 version, the Scoring Tool uses an expanded scoring method that maps a home to its local weather station and a unique 10-point scale for that climate location.
Under the initial HEScore program design for pilot tests, each of 19 geographic zones across the United States had a corresponding 10-point scale with source energy thresholds defined for each point on the scale. However, analysis showed that weather differences within each of the 19 zones are significant enough to skew scoring results. In fact, the scores of identical homes with different weather but within one geographic zone could vary by several points. As a result, the U.S. Department of Energy recognized the need to generate a larger set of 10-point scales for more than 240 different weather stations across the United States.
In an effort to more accurately account for climate differences, the final version of the HEScore Tool was used to estimate the source energy use for a range of homes in each of the 1000-plus weather station locations (refer to table example). The DOE then established energy values for the 10-point scale in each location based on the following guidelines and objectives:
- Understanding that both low- and high-efficiency homes will have large differences in source energy consumption around the country, the source energy scoring bins are sized to produce consistent score values per the performance level.
- The amount of energy reduction needed to move one point up the scale is set as low as possible while still allowing the vast majority of homes to score between 2 and 9 on the scale.
- The value between each point on the scale is constant for any one weather station.
- The maximum and minimum energy cut-offs corresponding to 1 and 10 on the scale also reflect the different types of housing stock found in various parts of the country.
With the preceding methodology, the HEScore label conveys concise information about a home’s absolute energy consumption and ranks the home on a consistent scale that applies across all U.S. regions. Because the energy budget is absolute energy consumption, calculated scores are sensitive to home size, meaning larger homes will tend to score lower (acknowledged within the Home Energy Score FAQs).