Since 2007, EPCs are now a legal requirement when selling or renting out your home. An energy efficiency survey is carried out on your home by a Domestic Energy Assessor and involves a variety of data gathering, including the type of heating systems present, glazing, loft & wall insulation and water heating. Once the data has been processed, the property is given an efficiency rating out of 100, where 100 is the most efficient and 0 is the least. The rating is also divided into letter bandings where A is the most efficient and G is the least.