Navien Condensing Tankless Water Heaters

The company offers three basic models of its tankless water heaters: the 180, 210, and 240; these units generate 150,000, 175,000, and 199,000 Btu/hr (44, 51, and 58 kW-thermal), respectively, with an output of 4.94 gallons per minute (gpm; 18.7 lpm) for the 240 model based on a 77ºF (43°C) rise. These units have low minimum firing rates between 15,000 and 17,000 Btu/hr (4.4–5.0 kW-thermal), low minimum water flows, and thermostats that monitor outgoing water temperature, which combine to produce consistent hot water. The residential models (labeled “CR”) incorporate corrosion-resistant stainless steel heat exchangers and copper tubing and are factory-set to provide hot water at a maximum temperature of 120ºF (49°C). They can be adjusted to temperatures as high as 140ºF (60°C), but higher temps require a mixing valve. The commercial “CC” models contain stainless steel tubing throughout the units for added durability and can generate water temperatures as high as 185ºF (85°C).

Both the residential and commercial units can be ordered as “A” models with added circulation pumps and 0.5-gallon (1.9 l) buffer tanks. These units have some advantages over the company’s standard CC and CR models, which, like most tankless water heaters, require a minimum water flow of at least 0.5 gpm (1.9 lpm) to activate the burner. The A model can handle flow rates as low as 0.1 gpm (0.4 lpm). When set to internal recirculation mode, water in the 0.5-gallon buffer tank circulates within the units, maintaining a pre-set temperature to produce consistent hot water while minimizing the hot and cold water stacking in the pipes known as a “cold water sandwich.” The recirculation system also provides protection from freezing in cold climates (these units are for indoor installation only) and can speed delivery of hot water through the pipes. Running the unit in internal recirculation mode does not significantly impact the unit’s overall efficiency, according to the company, though there will likely be some standby energy loss. These units can also be configured for external recirculation to fixtures, though this is typically less efficient than recirculation to a buffer tank.