ecoTough Series: Noritz introduces the latest advancements in tankless water heater technology for your home. The ecoTough High-Efficiency Series gives you unparalleled reliability and quality engineering and construction. It reduces energy use and CO2 emissions. The main features are endless hot water, less expensive PVC vented installation, and long life and reliability. Direct Vent: The NRC661 direct vent tankless water heater (condenser) enables your system to be installed in tight spaces indoors without the worry of combustion. Now, with the stainless steel and copper dual heat exchanger system, you can use PVC to safely vent the exhaust enabling you to save big on tankless water heater accessories. The quick connect system also enables multiple heaters to be connected and run by the same controller system for increased hot water demands. All of this functionality and efficiency are seamlessly controlled by a self-diagnostic computer system and digital remote, ensuring there is always perfect non-varying hot water for everyone to enjoy. Features: High-efficiency low NOx Eco-Burner reduces emissions Natural gas tankless hot water heater Indoor Use Only ecoTough tankless condensing heater Thermal efficiency: 92% Energy Star Factor: 0.91 Cold and Hot water connection size: 3/4" Gas connection size: 1/2" Power Supply: 120 VAC (60 Hz) Exhaust vent diameter requirements: 3" Exhaust vent material requirement: PVC or CPVC 5 Year Parts Warranty 1 Year Labor Warranty