Newbrunswick, NJ — This workshop describes how the HERS rating of a residence is generated, and how it is used to reduce energy use in both new and existing homes. The HERS Index is a single number describing all energy use in a residence. The use of on-site blower door and duct testing as input to the HERS rating is described. The Residential Energy Services Network (RESNET) established and maintains the nationally recognized Home Energy Rating System (HERS). The HERS index is used by the national EnergyStar program, the Massachusetts Stretch Code, lending institutions for Energy Efficiency Mortgages, the Massachusetts Zero Energy Challenge and the National Grid Deep Energy Retrofit pilot, as well as by leading edge design / build renovators who seek to 'push the envelope'.