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Comparison
Verdict in brief
Both are the same 150,000 BTU/h condensing tankless platform with identical published flow: 8.4, 6.5 and 4.3 GPM at 35, 45 and 67 °F rises. The NPE-180A2 adds Navien's ComfortFlow built-in buffer tank and recirculation pump, which reduces the cold-water sandwich and shortens the wait at the tap; the NPE-180S2 omits that hardware, publishes a slightly higher UEF of 0.96 against 0.95, and is 5 lb lighter. Choose the A2 when recirculation and steadier temperature are wanted; the S2 when they are not.
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-180A2Gas tankless | Navien NPE-180S2Gas tankless |
|---|---|---|
| Minimum gas input | 10,000 BTU/h | 10,000 BTU/h |
| Maximum gas input | 150,000 BTU/h | 150,000 BTU/h |
| Flow at a 35 °F (19.4 °C) rise | 8.4 GPM (31.8 L/min) at 35 °F (19.4 °C) rise | 8.4 GPM (31.8 L/min) at 35 °F (19.4 °C) rise |
| Flow at a 45 °F (25 °C) rise | 6.5 GPM (24.6 L/min) at 45 °F (25 °C) rise | 6.5 GPM (24.6 L/min) at 45 °F (25 °C) rise |
| Flow at a 67 °F (37.2 °C) rise | 4.3 GPM (16.3 L/min) at 67 °F (37.2 °C) rise | 4.3 GPM (16.3 L/min) at 67 °F (37.2 °C) rise |
| Minimum flow rate | 0.5 GPM (1.9 L/min); under 0.01 GPM option in ComfortFlow mode | 0.5 GPM (1.9 L/min) |
| Uniform Energy Factor (UEF) | 0.95 | 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 | 73 lb (33.1 kg) | 68 lb (30.8 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 flow tables are identical between the two 180 models: 8.4 GPM (31.8 L/min) at a 35 °F (19.4 °C) rise, 6.5 GPM (24.6 L/min) at 45 °F and 4.3 GPM (16.3 L/min) at 67 °F, with a 0.5 GPM activation point. Both modulate from 10,000 to 150,000 BTU/h, use the same 2 in or 3 in PVC, CPVC, polypropylene or stainless venting, 3/4 in gas and water connections, 120 V power, a condensate drain and a 10,100 ft altitude rating.
The hardware difference is ComfortFlow. The A2 carries a buffer tank and recirculation pump inside the cabinet; Navien's own documentation describes the buffer tank as reducing the cold-water sandwich common to tankless units and the pump as shortening the wait for hot water at the fixture. The S2 does not have that hardware, so its recirculation options are external and its electrical draw is listed without the A2's 350 W external-pump figure.
Efficiency and weight run slightly to the S2: UEF 0.96 against 0.95 for the A2, and 68 lb against 73 lb. Both are high-draw-class ratings on Navien's specification tables, and the difference is directional, not a savings percentage.
The practical choice turns on recirculation and temperature stability. The A2 is the unit for a home where the kitchen tap is far from the heater and a cold-water sandwich is the complaint; the S2 suits a layout with short runs or a home that does not need recirculation. Recirculation itself adds gas use, and either unit needs annual descaling to keep its warranty. Whether CANRO supplies a given model is confirmed at consultation.
Navien · Gas tankless
The Navien NPE-180A2 is the smallest of Navien's Canadian A2 condensing tankless models: 10,000–150,000 BTU/h on natural gas or propane, UEF 0.95, and published flows of 8.4 GPM at a 35 °F rise and 4.3 GPM at a 67 °F rise. It is a wall-hung, forced-draft direct-vent unit.
Navien · Gas tankless
The Navien NPE-180S2 is the smallest of Navien's current S2 condensing tankless models: 10,000–150,000 BTU/h on natural gas or propane, UEF 0.96, and published flows of 8.4 GPM at a 35 °F rise and 4.3 GPM at a 67 °F rise.
Yes. Both publish 8.4 GPM at a 35 °F rise, 6.5 GPM at 45 °F and 4.3 GPM at 67 °F, with the same 10,000–150,000 BTU/h input range and 0.5 GPM activation.
A buffer tank and recirculation pump built into the A2 cabinet. Navien describes the buffer tank as reducing the cold-water sandwich and the pump as shortening the wait for hot water. The S2 has neither.
The S2, on Navien's published figures: UEF 0.96 against 0.95 for the A2. Both are high-draw-class ratings and the gap is directional.
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 21, 2026. Last updated September 21, 2026. Technical reviewer: not yet assigned.