The NCB combi boiler line is Navien's signature product for hydronic-heat homes. A single wall-mounted unit provides both space heating (radiators, baseboards, in-floor radiant) and domestic hot water — replacing a separate boiler and water heater. The "C" in NCB stands for "combi."
NCB lineup
| Model | DHW BTU | Heat BTU | DHW GPM | Typical home |
|---|---|---|---|---|
| NCB-180E | 180,000 | 130,000 | 4.2 | 2 bath, small-medium |
| NCB-190 | 190,000 | 150,000 | 4.5 | 2-2.5 bath |
| NCB-210E | 210,000 | 170,000 | 5.0 | 2.5-3 bath |
| NCB-240 | 240,000 | 199,000 | 5.6 | 3 bath |
| NCB-240E | 240,000 | 199,000 | 5.6 | 3 bath (HeatGuard) |
| NCB-250 | 250,000 | 199,000 | 5.9 | 3-4 bath |
| NCB-300 | 300,000 | 240,000 | 7.0 | 4+ bath, larger home |
NCB vs NCB-E (HeatGuard)
NCB-E models add Navien's HeatGuard low-water-cutoff and additional safety logic. Required code in some jurisdictions. The non-E (NCB-240, NCB-190, etc.) base models lack the HeatGuard package but otherwise share the chassis.
When NCB is the right answer
- You have hydronic heating (radiators, baseboards, in-floor) and need to replace it
- You want to consolidate boiler + water heater into one unit
- You have limited mechanical room space
- You're switching from a forced-air system to hydronic and need both heat and DHW from one source
When NCB is NOT the right answer
- You have forced-air heat — your home doesn't need a boiler; an NPE tankless is the right product
- Very large homes with high heat demand — consider a separate NHB heating boiler + dedicated DHW tank for capacity reasons
- Budget is tight — combi installs add hydronic plumbing complexity and cost
Combi sizing
Combis are sized by combined demand:
- Heating load: calculate with Manual J (heat loss analysis)
- DHW peak demand: simultaneous showers, dishwasher, etc.
- The combi must satisfy both — but heating gets priority lock-out during DHW draws (combi pauses heat for the few minutes of a shower)
Most US homes (1,500-3,000 sq ft, 2-3 bathrooms) fit NCB-180E to NCB-240. Larger homes (3,500+ sq ft or 4+ bathrooms) need NCB-250 or NCB-300.
Hydronic install requirements
Combi installs are significantly more complex than tankless. Required:
- Primary/secondary loop with hydraulic separator or closely-spaced tees
- Expansion tank sized for system volume
- Air and dirt separator
- Backflow preventer on fill loop
- Outdoor reset sensor for modulating supply temp
- Zone valves or circulators for multi-zone homes
Use a Navien Service Specialist or hydronics-experienced contractor — generic plumbers often miss the design requirements. See install guide.
Warranty
10 years heat exchanger / 5 years parts / 1 year labor — residential. See warranty hub.
NCB vs NFC fire-tube
The NFC line (NFC-250) uses a fire-tube heat exchanger vs NCB's water-tube. NFC offers smoother modulation, longer service life, and 15-year heat exchanger warranty (vs NCB's 10). Costs more — typically $700-1,000 premium.
Pricing
- NCB-180E: $2,300-2,700
- NCB-190: $2,500-2,900
- NCB-210E: $2,600-3,000
- NCB-240: $2,800-3,300
- NCB-240E: $2,900-3,400
- NCB-250: $3,000-3,500
- NCB-300: $3,300-3,900
Installation adds $3,500-7,000+ depending on hydronic system complexity, demolition of old boiler, and venting/condensate work.
Bottom line
NCB is the standard answer for replacing an old boiler/water-heater pair with a single high-efficiency unit. NCB-240 is the volume model — sized for 3-bathroom homes with moderate heating load. Choose NFC if you can stretch budget and want longer warranty/service life.