The DOE took into account many different factors as well as available sources of data in an effort to develop a scoring system that could fairly compare the energy performance of existing homes. The DOE sought to develop a simple system that allows consumers to understand how a home compares to other homes regardless of location and weather patterns. The current methodology is applicable to single-family homes and townhouses in the continental US.
The tool scores a home on a 10-point scale, where a 10 corresponds to greatest efficiency (minimal energy use). Each point on the scale corresponds to a specific source BTU level. National average source energy factors were used to calculate a total energy value for electricity, natural gas, liquified propane gas and distillate fuel oil energy sources delivered to the home. The source energy factors are from the Energy Star Portfolio Manager Technical Reference (US EPA, 2013).
a consistent set of upgrade recommendations must be considered for each home (variations in which are recommended as a function of home characteristics, cost-effectiveness, etc.). Upgrades considered in the Scoring Tool include improvements to the home envelope and major equipment (the "assets"), but not to lighting and appliances or usage changes. Unlike the other Home Energy Saver tools, the Scoring Tool applies a fixed, standardized retrofit cost (from the NREL National Residential Efficiency Measures Database) and generates recommendations providing the highest performance level with a payback time of 10 years or less. Energy savings are those achieved by moving between the existing home and the level of the deemed efficiency level of the upgrade.
The following two categories and specific upgrades are currently provided by the Scoring Tool:
Type 1 - Improvements recommended now - These upgrades can help you save energy right away
Type 2 - Recommendations for when you need to replace equipment – These recommendations will help you save energy when it's time to replace or upgrade.
It is important to note that the sum of the savings from the individual measures of the recommendations report may not equal the total savings for the package of selected upgrades (the number shown on the label). This difference is due to interactive effects of individual energy improvements. When improvements reduce energy consumption within the same end-use (e.g., a window upgrade plus an air conditioner upgrade), the resulting dollar savings is less than the sum of the savings shown for the individual improvements.