HERS Rating of 150: A home with a 150 HERS rating uses 50% more energy than a new home built to standard energy code. Most older homes will rate above to way above 100 on the HERS index. Some older homes can exceed HERS index scores of over 200.
HERS Rating of 100: A new home constructed and tested to meet the current building code standard for home energy efficiency will rate 100 on the HERS index.
Rating 100 does not mean the home is considered to be energy efficient from a green building standard, only that it meets the code standard code, which is the lowest acceptable level of energy efficiency allowed by code.
HERS Rating of 50: A HERS rating of 50 means your home uses 50% less the energy than a new home built to code and, on average, 80% less than a resale home uses.