Takagi’s TK-510C-NI is a fully modulating, gas-fired, tankless water heater with sealed combustion and power vented flue. Featuring 199,000 Btu, the heater supplies hot water to domestic hot water systems (directly or indirectly) and can be used with water storage tanks, recirculation systems, and/or combined domestic and heating applications. It complies with ultra-low NOx regulations of less than 14 ng/J (20ppm). It features: an Energy Factor of 0.82 for natural gas or liquid propane, a maximum flow rate of 10 gal. per min. at 35° F temperature rise.