Navien NCB-250 Combi Boiler with Tankless Water Heater

The Navien NCB-250 is the largest residential combination boiler in Navien's NCB line, providing both 250,000 BTU space heating and 9.0 GPM domestic hot water from a single appliance. Sized for larger homes (2,500-4,000 sq ft) with substantial hydronic space-heat demand.

Specs: 250,000 BTU input, AFUE 95%, 9.0 GPM DHW at a 70°F rise, fully modulating burner with 5:1 turndown. Built-in 0.5-gallon buffer with ComfortFlow recirculation for DHW. PVC condensing venting. 15-year warranty on heat exchanger.

The combi format consolidates space heat + DHW into a single appliance. For larger homes converting from aging oil-fired boiler + separate water heater, the NCB-250 replaces both with a high-efficiency unit. The fully modulating burner reduces short-cycling during partial-load conditions versus the older two-stage boilers it typically replaces.

Right buyer: larger home (2,500-4,000 sq ft) replacing aging boiler + water heater with single high-efficiency combi unit. Typical install $10,000-$14,000 including hydronic system modifications. Wrong buyer: pure DHW applications, smaller homes (NCB-190 is appropriately sized).