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.