Navien NCB-240E Combi Boiler with Tankless Water Heater

The Navien NCB-240E Combi Boiler with Tankless Water Heater is a hybrid product — combination space-heating boiler and tankless water heater in a single wall-mounted unit. 95% AFUE on the heating side, 0.95 UEF on the DHW side, 11.6 GPM domestic hot water, 80,000 BTU heat input. Right pick when you're upgrading both boiler and water heater simultaneously and want a single integrated unit.

Headline specifications

• Type: condensing combi boiler with integrated tankless DHW, natural gas (LP-convertible)
• Space heat output: 80,000 BTU/h (heating side)
• DHW max flow: 11.6 GPM at 35°F rise
• AFUE heating efficiency: 95%
• DHW UEF: 0.95
• Modulation: 10:1 turndown
• Warranty: 10-year heat exchanger, 5-year parts
• NaviLink WiFi standard
• Venting: PVC/CPVC up to 100 ft
• Dimensions: 32" H × 18" W × 14" D
• Wall-mounted

Who this model is for

The NCB-240E is for homes with hydronic space heating (boiler-driven radiators, baseboards, or radiant floors) plus domestic hot water demand. Northeast and Midwest homes with cast-iron boilers reaching end of life — typical install is replacement of a 1970s–1990s atmospheric cast-iron boiler that also fed an indirect tank for hot water. The NCB-240E replaces both in one unit, frees up 4–6 sq ft of mechanical-room floor space, and cuts gas use ~25% via the 95% AFUE upgrade.

Wrong product for homes with forced-air heat — that's not what this is. Forced-air heat homes want a furnace + standalone water heater (gas or tankless), not a combi.

Also wrong product if your house has high simultaneous heat-and-DHW demand — combi boilers prioritize DHW, so on the coldest day with a long shower running, space heating may temporarily drop. Heat-priority homes need a separate boiler + tank combo or a higher-capacity combi.

Where the NCB-240E beats the alternatives

Vs separate boiler + indirect tank: NCB-240E replaces two appliances with one. Saves $1,000–$2,500 in install cost (fewer connections, single vent, single gas drop) and ~25% on annual gas use via 95% AFUE.

Vs NPE-240A2 standalone tankless + retained old boiler: NCB integrates space heating at 95% AFUE — if your boiler is also at end of life, the combi solves both problems. If the boiler is healthy, standalone tankless is the right pick.

Vs traditional gas tank + boiler: floor space, fuel cost, install simplicity all favor the combi if you're replacing both anyway. Gas tank + boiler favored if budget is tight (you can replace one and defer the other).

Where it falls short

Combi boilers in homes with intermittent or low DHW demand have a downside — the unit cycles frequently because DHW flow is low but the burner ignites for short bursts, which reduces overall efficiency vs sustained-run operation.

DHW priority means space heating can briefly dip during long simultaneous showers + heating-demand events. Acceptable in most climates; problematic if you live somewhere with -10°F nights and 30-minute teenager showers.

Installer expertise matters. Combi boilers are not the same as standalone tankless. Verify your installer has Navien NCB-specific training, not just Navien NPE certification.

10-year heat exchanger warranty is shorter than the NPE-A2 15-year warranty. Combi boilers operate at higher duty cycle (heat + DHW combined) — Navien accounts for this in the warranty scaling.

Wall-mounted installation requires structural anchor capable of carrying ~80 lbs. Verify wall framing.

Install considerations

3/4" gas line required. PVC/CPVC venting up to 100 ft. 120V outlet. Connections for both DHW (hot and cold) and hydronic (supply and return) loops. Permit required. Licensed boiler-certified installer required in most jurisdictions.

Install cost: $4,500–$8,500 for typical boiler+tank-to-combi conversion (significantly higher than tankless DHW alone because hydronic plumbing is involved). New construction: simpler, $3,500–$6,000.

Maintenance

• Annual descaling (DHW side)
• Annual hydronic system check (expansion tank, glycol level if applicable, pressure)
• NaviLink firmware updates
• Burner inspection by combi-certified technician every 2 years
• Hydronic loop flush every 5 years

Bottom line

The Navien NCB-240E is the combi-boiler-plus-tankless-DHW pick for homes with hydronic heating and simultaneous boiler-and-water-heater replacement needs. 95% AFUE, 0.95 UEF, 11.6 GPM DHW. Right pick for Northeast/Midwest hydronic-heated homes upgrading from atmospheric cast-iron boiler + indirect tank. Wrong pick for forced-air homes (use NPE-240A2 standalone) or homes where the existing boiler still has life (defer the combi conversion).