RESNET HERS Explained

The Residential Energy Services Network (RESNET) was founded in 1995 to develop a national market for home energy rating systems and energy efficient mortgages. RESNET is an industry not-for-profit membership corporation. It is a national standards-making body for building energy efficiency rating systems.

Who recognizes RESNET Standards?

  • Mortgage industry for capitalizing energy efficiency in mortgages
  • Financial industry for certification of "white tags"
  • States for minimum code compliance in 16 states
  • Federal government for verification of building energy performance for:
    • Federal tax credit qualification
    • EPA ENERGY STAR labeled homes
    • U.S. Department of Energy Building America program

What are the results of a rating?

  • A relative energy use index called the HERS® Index - a HERS Index of 100 represents the energy use of the "American Standard Building" and an Index of 0 (zero) indicates that the Proposed Building uses no net purchased energy (a Zero Energy Building)
  • A set of rater recommendations for cost-effective improvements that can be achieved by the Rated Building

How Does the HERS Index Work?

A home is given a score based on an in-depth assessment conducted by a RESNET Home Energy Rater. The rating provides a comparative analysis on how energy efficient a home is in comparison to other similar homes, using a benchmark. It provides a measure of the relative energy use of the home based on its physical characteristics and a standardized set of operating characteristics. The lower the score, the less energy the home uses.

How is the HERS Index calculated?

Computer software is used to analyze the results of an in-depth assessment of an existing home or the components of a new home design. The assessment includes analysis and inspection of windows, doors, insulation and ducts to determine the amount and location of leaks. All heating and cooling equipment is evaluated based on type, characteristics and age. Appliances and lighting are inspected along with any existing or potential combustion safety issues. Specialized diagnostic equipment, as well as computer software, are used to compile a detailed report. In addition to yielding an energy rating, the report will provide a cost benefit/analysis, with expected return on investment for suggested repairs and upgrades. This makes it easier to prioritize recommended treatments.

  • RESNET Home Energy Rating SystemProposed (or As-built) Building and the Standard Building are modeled using accredited building simulation software tools and the results are ratioed (Proposed divided by Standard times 100)
  • Software accreditation is achieved by passing a battery of software verification tests developed by U.S. National Laboratories and RESNET
  • Software is required to automatically generate the Standard Building using only the input from the Proposed Building (i.e. software users have no control over the configuration and modeling of the Standard Building)
  • Configuration and modeling parameters for the Standard Building are carefully and completely specified as a modeling "rule set."

How is the Number Used?

We can’t evaluate what we can’t measure and this is where energy ratings come in to play. A RESNET HERS Rating allows one home’s performance to be compared against another. The assessments allow buyers to estimate the cost of maintaining their home and evaluate the cost-effectiveness of options that can improve energy efficiency. Builders are modifying designs based on rating guidelines to meet buyer demand for maximum comfort at a minimal cost. Mortgage companies recognize ratings as a tool and require them to qualify loan applicants for certain federally sponsored mortgage products. Some states use the RESNET HERS Rating in establishing minimum code compliance. The HERS Index is one of the metrics used to qualify a home for an EPA Energy Star label.

How does RESNET provide for quality assurance within the Rating industry?

  • Each Rating Provider must employ a certified Quality Assurance Designee
  • Quality Assurance Designee must independently verify internal consistency of a minimum 10% of all building input files
  • Quality Assurance Designee must independently field verify the accuracy of a minimum of 1% of each certified Rater's homes
  • RESNET monitors the Rating Providers compliance with quality assurance requirements

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