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The Maximum Input Capacity describes how quickly the appliance will use fuel when delivering it's maximum capacity. The units may change depending on the fuel being used.

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Energy Factor (EF) is a measurement of water heater energy efficiency. The higher the energy factor, the more efficient the water heater. Learn More

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AFUE (Annual Fuel Utilization Efficiency) measures the efficiency of combustion equipment over the entire heating season, and is calculated by dividing the amount of energy that is actually heating your home by the total energy contained in the fuel used by the boiler/furnace. Learn More

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To create heat, some form of fuel is required. Fuel Type specifies what the product uses as an input to create heat.

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Flow rate measures how much hot water your heater can deliver. Click Learn More to determine the appropriate temperature rise to use based on your location. Learn More

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Noritz NCC1991 - 6.2 GPM at 60° F Rise - 94% Eff. - Gas Tankless Water Heater - Direct Vent (Scratch & Dent) EnergyStar Commercial Water Heater. Ultra Low NOx Emissions (SCAQMD Rule 1146.2 Compliant). Ratings: 9.3 GPM at 40° F Rise, 7.4 GPM at 50° F Rise, 6.2 GPM at 60° F Rise, 5.3 GPM at 70° F Rise. 188k Effective BTU/h.