Understanding the HERS Index

What does the HERS Index say about a house?

The HERS Index is a measurement of a home’s energy efficiency and there are a lot of great reasons why you should have a home energy rating performed on your house.

A HERS Index Score can tell you so much about a home you are thinking of buying. Heating, cooling and water heating constitute the largest cost of homeownership outside of the mortgage loan. The HERS Index Score will tell you how well the home performs energy-wise. The HERS Report will outline the energy features of the home and the expected cost of utility bills.

It will also provide you with invaluable information about the existing home you live in, like how efficiently it’s operating and where you can make modifications for greater energy savings. When you're selling your home, a low HERS Index Score can command a higher resale price. And when you’re buying a home, you can anticipate the costs of energy bills and efficiency upgrades.

How does the HERS Index work?

A certified RESNET Home Energy Rater assesses the energy efficiency of a home, assigning it a relative performance score (the HERS Index Score). The lower the number, the more energy efficient the home. The U.S. Department of Energy has determined that a typical resale home scores 130 on the HERS Index while a home built to the 2004 International Energy Conservation Code is awarded a rating of 100.

  • A home with a HERS Index Score of 70 is 30% more energy efficient than the RESNET Reference Home.
  • A home with a HERS Index Score of 130 is 30% less energy efficient than the RESNET Reference Home.

To calculate a home’s HERS Index Score, a certified RESNET HERS Rater does an energy rating on your home and compares the data against a 'reference home'– a designed-model home of the same size and shape as the actual home, so your score is always relative to the size, shape and type of house you live in.

Some variables included in an energy rating are:

  • All exterior walls (both above and below grade)
  • Floors over unconditioned spaces (like garages or cellars)
  • Ceilings and roofs
  • Attics, foundations and crawlspaces
  • Windows and doors, vents and ductwork
  • HVAC system, water heating system, and your thermostat.
  • Air leakage of the home
  • Leakage in the heating and cooling distribution system