The Home Energy Rating System (HERS) is a national standard for measuring the energy efficiency of a home. The HERS standards are developed and maintained by RESNET (Residential Energy Services Network), a not-for-profit association of rating providers, state and national government agencies, academics, research institutes, energy companies, manufacturers and others.
The national RESNET standards define the procedures for rating new and existing homes, for auditing existing homes, for training and certifying raters and for managing a nationally-consistent quality assurance process. HERS ratings are determined by qualified raters who are working under the supervision of RESNET-accredited HERS Providers like Home Energy Technologies. The rating Providers ensure rating quality and consistency through rater training and the RESNET QA process. Raters may be employees of the Provider or may be independent raters working under a provider agreement.
A HERS rating is an index number that expresses the energy efficiency of a home, somewhat like the mpg rating for an automobile. It is determined by dividing the projected energy consumption of the home by the projected energy consumption of a reference home and multiplying by 100. The reference home is a home of the same dimensions in the same climate zone that is built according to the standards of the model energy code and has a HERS index of 100. A home with a HERS index of 0 is called a Zero Energy Home and to achieve this performance a home must be equipped with sufficient renewable power generation sources (e.g photovoltaics, wind, solar water heating) to equal the home's energy usage for heating, cooling, hot water, lights and appliances. Older homes typically have a HERS index well over 100 unless their insulation and mechanical systems have been brought up to modern standards.
Because it is an objective, standardized metric the HERS index of a home is used in determining eligibility for many program certifications. Among our program partners it is used for ENERGY STAR qualification, the National Green Building Standard qualification, determining rebates in the CT Energy Efficiency Fund’s Residential New Construction Program and for qualification as a Zero Energy Ready Home.
To calculate the energy consumption of a home for a HERS rating the software considers the areas and insulation values of the thermal envelope (walls, windows, ceilings, floors,
etc), the efficiency of the heating, cooling and hot water systems, the lighting system, the appliances and energy losses through air infiltration and duct leakage. This energy modeling enables us to project a home’s energy consumption and rating at the design stage when it is still possible to evaluate options for insulation and systems to develop the most cost effective energy strategy.