A.O. Smith GDV-40 ProMax Direct-Vent Gas Water Heater, 40 gal One-pipe, dual-channel draws all make-up air from outside the home, eliminating problems caused by insufficient indoor ventilation Internal microprocessor provides enhanced operating parameters and tighter differentials for precise sensing and faster heating response Dynaclean diffuser dip tube helps reduce lime and sediment buildup, maximizes hot water output; made from long-lasting PEX cross-linked polymer Self-powered electronic gas valve uses thermopile to generate power needed to operate the electronic gas control without requiring external power The electronic gas control incorporates and LED status indicator that monitors system operation and service diagnostics