HERS stands for Home Energy Rating System and was established in the early 1990s as a method to calculate and put a number on the energy efficiency of a residence. The first raters were certified in the early to mid-1990s. The ratings produced by these first raters were to be utilized by mortgage lenders to allow a home buyer to extend their debt to income ratio if buying a home already up to energy standards, or to allow more money to be included in the mortgage so energy efficiency upgrades could be installed in a newly purchased home. The HERS rating gave a number to a home energy conservation performance much like a “miles per gallon” number for a car. These types of raters are also known as “whole house raters” and require special certification to perform these ratings.