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Comparison
Verdict in brief
These are the two ends of Navien's current S2 condensing tankless line in the same 17.3 in cabinet. The NPE-150S2 is 18,000–120,000 BTU/h, UEF 0.93 and rates 6.8 GPM at a 35 °F rise and 3.4 GPM at a 67 °F rise; the NPE-240S2 is 13,300–199,900 BTU/h, UEF 0.96 and rates 11.2 GPM at 35 °F and 5.8 GPM at 67 °F. Metro Vancouver's winter rise to a 49 °C shower approaches 40 °C (72 °F), so the 67 °F row is the sizing number: the 150S2 is a one-fixture-at-a-time unit in January, the 240S2 is marginal for two simultaneous showers.
Published manufacturer figures with units. Storage and flow figures are different measures and are shown on their own rows; blanks mean not applicable or not published.
| Specification | Navien NPE-150S2Gas tankless | Navien NPE-240S2Gas tankless |
|---|---|---|
| Minimum gas input | 18,000 BTU/h | 13,300 BTU/h |
| Maximum gas input | 120,000 BTU/h | 199,900 BTU/h |
| Flow at a 35 °F (19.4 °C) rise | 6.8 GPM (25.7 L/min) at 35 °F (19.4 °C) rise | 11.2 GPM (42.4 L/min) at 35 °F (19.4 °C) rise |
| Flow at a 45 °F (25 °C) rise | 5.3 GPM (20.1 L/min) at 45 °F (25 °C) rise | 8.7 GPM (32.9 L/min) at 45 °F (25 °C) rise |
| Flow at a 67 °F (37.2 °C) rise | 3.4 GPM (12.9 L/min) at 67 °F (37.2 °C) rise | 5.8 GPM (22.0 L/min) at 67 °F (37.2 °C) rise |
| Minimum flow rate | 0.5 GPM (1.9 L/min) | 0.5 GPM (1.9 L/min) |
| Uniform Energy Factor (UEF) | 0.93 | 0.96 |
| Vent type | 2 in or 3 in PVC, CPVC, approved polypropylene or stainless steel; special gas vent type BH (Class II A/B/C) | 2 in or 3 in PVC, CPVC, approved polypropylene or stainless steel; special gas vent type BH (Class II A/B/C) |
| Gas connection | 3/4 in | 3/4 in |
| Water connections | 3/4 in cold inlet and hot outlet | 3/4 in cold inlet and hot outlet |
| Electrical supply | 120 V AC, 60 Hz; up to 200 W (2 A), 350 W (4 A) with external pump | 120 V AC, 60 Hz |
| Height | 27.4 in (696 mm) | 27.4 in (696 mm) |
| Width | 17.3 in (439 mm) | 17.3 in (439 mm) |
| Depth | 13.2 in (335 mm) | 13.2 in (335 mm) |
| Weight | 62 lb (28.1 kg) | 73 lb (33.1 kg) |
| Maximum altitude | 10,100 ft for natural gas and propane | 10,100 ft for natural gas and propane |
“—” means not applicable to that system type or not published by the manufacturer. Flow figures are only comparable at the same temperature rise; UEF values are only comparable within the same draw pattern.
The two share the S2 platform completely: forced-draft direct venting in 2 in or 3 in PVC, CPVC, approved polypropylene or stainless (or BH special gas vent), 3/4 in gas and water connections, a 0.5 GPM (1.9 L/min) minimum flow, 120 V power, a maximum altitude of 10,100 ft and the same 17.3 in wide, 27.4 in high, 13.2 in deep cabinet. Both support Navien's recirculation configuration with an external pump or crossover accessory.
What separates them is the heat input and the flow it produces. Navien publishes flow at three rises, which makes the comparison honest: at the 67 °F (37.2 °C) rise that matches a Metro Vancouver winter, the NPE-150S2 delivers 3.4 GPM (12.9 L/min) against the NPE-240S2's 5.8 GPM (22.0 L/min). A shower-class fixture draws about 7.5 to 9.5 L/min, so the 150S2 covers one at a time in winter and the 240S2 is marginal for two at once.
Efficiency moves with the size: UEF 0.93 on the NPE-150S2 against 0.96 on the NPE-240S2, both high-draw-class ratings on Navien's specification table. Navien marks the NPE-150S2 not ENERGY STAR certified on its product page. The 150S2 is also the lightest S2 unit at 62 lb (28.1 kg) against 73 lb (33.1 kg), though the cabinet dimensions are identical.
The choice is a demand question. Suites, laneway homes and one-bathroom houses with sequential use fit the NPE-150S2 and its lower gas draw; a larger home with simultaneous fixtures or a higher winter rise needs the NPE-240S2 or a demand assessment that may point to a different size in the same line. The gas supply and vent route are confirmed before either is specified, and whether CANRO stocks a model for a job is confirmed at consultation.
Navien · Gas tankless
The Navien NPE-150S2 is the smallest of Navien's current S2 condensing tankless models: 18,000–120,000 BTU/h on natural gas or propane, UEF 0.93, and published flows of 6.8 GPM at a 35 °F rise and 3.4 GPM at a 67 °F rise.
Navien · Gas tankless
The Navien NPE-240S2 is the largest of Navien's current S2 condensing tankless models: 13,300–199,900 BTU/h on natural gas or propane, UEF 0.96, and published flows of 11.2 GPM at a 35 °F rise and 5.8 GPM at a 67 °F rise.
It depends on the winter peak. At its 67 °F-rise rating of 3.4 GPM it serves one fixture at a time in January; a house that runs two showers together is assessed for a larger S2 size instead.
They share the S2 venting and connection pattern, but the gas line and meter are sized to the input: 120,000 BTU/h on the 150S2 against 199,900 BTU/h on the 240S2. A supply check is part of the assessment.
The NPE-240S2 is rated UEF 0.96 against the NPE-150S2's 0.93, both at the high draw class. A higher UEF is not a savings percentage and is not compared across draw patterns.
A consultation includes a hot-water demand review so capacity is right for your winter, not the brochure's.
On-site service in Metro Vancouver, BC. Call to check availability.
Sources and verification
Facts checked September 19, 2026. Last updated September 19, 2026. Technical reviewer: not yet assigned.