These High EF Extra Recovery (XR) TTW® models feature increased insulation for higher energy factor ratings. Additionally, the XR models feature higher BTU inputs. This translates to an increased amount of hot water available offering unprecedented first hour delivery ratings (99 & 110 gallons) at a usable temperature in less time than normal. High EF Extra Recovery XR TTW® models are power vented for positive exhaust. They offer greater installation flexibility with the ability to vent through a wall or roof, with either 3" or 4" PVC, CPVC or ABS. And best of all, they qualify for ENERGY STAR®.