3 Panel Sliding Glass Doors from The Window Source Atlanta are a great energy efficient upgrade. This sliding patio door replaced a drafty metal sliding glass door from the 1970’s. The old sliding glass door was single pane and very costly on the energy bills for this customer. Old single pane sliding glass doors can let in tremendous amounts of heat during the summer, making cooling of a single room almost impossible. Now this customer can enjoy lower energy bills and a beautiful new sliding glass door.