**Navien combi-boilers are condensing, gas-combination boilers that can simultaneously produce hydronic heat and domestic hot water.** Navien produces three NCB Series combi-boilers, the NCB-180, NCB-210 and NCB-240, each of which has a different BTU rating and hot water flow rate, as of 2015.

The NCB-180 is the smallest of the three Navien combi-boilers, which has a maximum hydronic heat input rating of 80,000 BTU's per hour and an average hot water flow rate of 3.4 gallons per minute. The medium-sized NCB-210 is rated at 100,000 BTU's per hour and has a hot water flow rate of 4.0 gallons per minute. The NCB-240 is the largest of the three Navien combi-boilers, with a rating of 120,000 BTU's per hour and a hot water flow rate of 4.5 gallons per minute. This gives the NCB-240 model the highest combined hot water flow rate and heating capacity in the industry, as of February 2015.

One of the major advantages of the Navien NCB Series combi-boilers is the fact that these units take up approximately 80 percent less space than a traditional, floor-standing water heater and boiler, while still providing comparable hot water flow rates and heating capabilities. All three models are powerful enough to fully heat a large home, while simultaneously providing enough hot water to run two showers and a dishwasher.