Energy, Eco & Environmentally Friendly. Our systems are some of the most complete and advanced on the market. Window Energy Rating is a method for assessing the total energy performance of a complete window. It clearly shows the products that can save customers money and assist in the reduction of Co2 emissions. Windows and doors have traditionally been the main areas of energy loss in buildings which can be avoided by installing Egan Windows energy efficient windows. We focus on many performance factors: Low emissivity glass, the type of gas fill, the size of the cavity, spacer bars and the edge sealants. Within the outer frame and sash, insulating foam or thermal barrier technologies can be used.