Quick Answer: The Navien NPE-240S2 is a strong pick for homes that need one 199,900 BTU gas tankless heater and don’t need a built-in recirculation pump. ENERGY STAR rates it 0.96 UEF and 5.8 GPM at a 67°F rise, level with the Rinnai RX199iN and Rheem IKONIC on flow, and SupplyStop listed it at $1,810.00 on November 4, 2026, $389 less than the pump-equipped NPE-240A2. Size it with Navien’s temperature-rise table, not the 11.2 GPM headline: set to 120°F, it delivers 4.6 GPM from 35°F groundwater and 6.0 GPM from 55°F. Buy it through a licensed installer, because Navien’s warranty page says internet purchases void the warranty.
Last updated November 4, 2026: specifications and warranty terms checked against Navien’s NPE-240S2 product page, NPE-S2 series page, NPE-S2 warranty page and NPE-S2 FAQ; efficiency and gas use against ENERGY STAR’s certified water heater database; prices against SupplyStop; recall history against the CPSC recall database. We compare published specs, prices and terms; we don’t test heaters ourselves.
Most write-ups of the NPE-240S2 repeat three numbers from the box: 199,900 BTU, 11.2 GPM and 15 years. Navien’s own paperwork adds conditions to each of them. This review goes through the spec table, the temperature-rise chart and the warranty page, compares the S2 with its pump-equipped A2 twin and the rest of the NPE-S2 line, and sets it against the two heaters it is most often cross-shopped with. For the full Navien range, see our best Navien tankless water heater guide.
Navien NPE-240S2 specs at a glance
| Spec | Navien NPE-240S2 | Source |
|---|---|---|
| Type | Condensing gas tankless, indoor or outdoor wall-hung | Navien spec table |
| Gas input | 13,300 to 199,900 BTU/h, natural gas or propane (15:1 turndown) | Navien spec table, NPE-S2 series page |
| Efficiency | 0.96 UEF | ENERGY STAR, Navien |
| Rated flow | 11.2 GPM at a 35°F rise | Navien |
| Flow at federal test rise (67°F) | 5.8 GPM | ENERGY STAR, Navien |
| Minimum flow | 0.5 GPM | Navien spec table |
| Estimated gas use | 176 therms a year (ENERGY STAR); 177 therms, $193 a year at $1.09 a therm (Navien) | ENERGY STAR, Navien |
| Propane use | 194 gallons a year, $468 at $2.41 a gallon | Navien |
| Size and weight | 17.3 x 27.4 x 13.2 in; 73 lb | Navien spec table |
| Connections | 3/4 in NPT cold, hot and gas | Navien spec table |
| Gas supply pressure | 3.5 to 10.5 in WC natural gas; 8 to 13 in WC propane | Navien spec table |
| Water pressure | 15 to 150 PSI | Navien spec table |
| Venting | 2 or 3 in PVC, CPVC, polypropylene or stainless; 2 in PVC up to 75 ft; 0 in clearance to combustibles | Navien product page |
| Electrical | 120 V; 200 W max (2 A), 350 W (4 A) with an external pump connected | Navien spec table |
| Altitude | Up to 10,100 ft on natural gas or propane | Navien spec table |
| Emissions and listings | Under 20 ppm NOx (SCAQMD 1146.2), CSA, NSF 5, low lead, AHRI 206368362 | Navien QuickFacts |
| Heat-exchanger warranty | 15 years residential (5 years with uncontrolled recirculation) | Navien NPE-S2 warranty |
By the numbers
- 0.96 UEF and 5.8 GPM at a 67°F rise: ENERGY STAR’s listing for the NPE-240S2 (certified February 2023, checked November 4, 2026). The Rinnai RX199iN and Rheem IKONIC ECOHS200iN post the same 5.8 GPM.
- 4.6 GPM from 35°F groundwater: Navien’s own temperature-rise table at an 85°F rise, which is what a 120°F setting asks for in a northern winter. The 11.2 GPM headline needs a 35°F rise.
- $389: the price gap between the NPE-240S2 ($1,810.00) and the pump-equipped NPE-240A2 ($2,199.00) at SupplyStop on November 4, 2026.
- 176 vs 178 therms a year: ENERGY STAR’s gas-use estimates for the S2 and the A2. At $1.50 a therm, the S2 saves about $3 a year.
- 1 year of labor: Navien’s residential warranty table for the NPE-S2. The 15-year term covers the heat exchanger, and parts get 5 years.
- Up to 32 units can be cascaded with Navien’s Ready-Link cable, and up to 12 can share a common vent, according to the NPE-S2 series page.
What the NPE-240S2 actually delivers in winter
Tankless output depends on how many degrees the burner has to add. Navien publishes a temperature-rise table for the NPE-240S2 from a 35°F rise to a 140°F rise. Below, we matched it to groundwater temperatures for a 120°F setting and added how many 2-GPM showers that flow can run at a 105°F mixed temperature (our calculation: each shower draws 1.33 to 1.65 GPM of hot water, depending on how cold the inlet is).
| Groundwater temperature | Temperature rise to 120°F | NPE-240S2 max flow (Navien) | 2-GPM showers at once (our math) |
|---|---|---|---|
| 35°F | 85°F | 4.6 GPM | 2.8 |
| 40°F | 80°F | 4.9 GPM | 3.0 |
| 45°F | 75°F | 5.2 GPM | 3.2 |
| 50°F | 70°F | 5.6 GPM | 3.6 |
| 55°F | 65°F | 6.0 GPM | 3.9 |
| 60°F | 60°F | 6.5 GPM | 4.3 |
| 65°F | 55°F | 7.1 GPM | 4.9 |
| 70°F | 50°F | 7.8 GPM | 5.6 |
| 75°F | 45°F | 8.7 GPM | 6.5 |
Flow figures are from the temperature-rise table on Navien's NPE-240S2 product page (35°F to 140°F rise in 5 to 10°F steps). Use your own winter inlet temperature; a higher setpoint than 120°F lowers the flow.
The practical reading: across the northern US, an NPE-240S2 runs about three showers at once in winter, and about four where groundwater sits in the mid-50s. That is the same ceiling every 199,000 BTU heater hits. Rinnai’s groundwater chart gives its RX199iN 4.6 GPM at 35°F inlet as well, so neither brand has a hidden flow advantage. If you need more, the NPE-S2 cascades: two units on Navien’s Ready-Link cable double the burner. Our tankless sizing guide works through the same math for other heaters.
NPE-240S2 vs NPE-240A2 vs the rest of the NPE-2 line
Navien sells the NPE-2 condensing line in two versions. The S2 models have no pump. The A2 models add ComfortFlow, which Navien describes as a buffer tank plus a recirculation pump with its own controls. Both share the same 17.3 x 27.4 x 13.2 inch cabinet. The S2 series now also includes a smaller NPE-150S2, which has no A2 twin. Navien doesn’t show prices, so the prices below are from SupplyStop, checked November 4, 2026.
| Model | Max input | UEF | GPM at 35°F rise | GPM at 67°F rise | Pump | Weight | SupplyStop |
|---|---|---|---|---|---|---|---|
| NPE-240S2 | 199,900 BTU | 0.96 | 11.2 | 5.8 | No | 73 lb | $1,810.00 |
| NPE-240A2 | 199,900 BTU | 0.95 | 11.2 | 5.6 | Yes (ComfortFlow) | 77 lb | $2,199.00 |
| NPE-210S2 | 180,000 BTU | 0.96 | 10.1 | 5.3 | No | 73 lb | $1,699.00 |
| NPE-210A2 | 180,000 BTU | 0.95 | 10.1 | 5.1 | Yes | 77 lb | $1,980.00 |
| NPE-180S2 | 150,000 BTU | 0.96 | 8.4 | 4.3 | No | 68 lb | $1,550.00 (out of stock) |
| NPE-180A2 | 150,000 BTU | 0.95 | 8.4 | 4.3 | Yes | 73 lb | $1,849.00 |
| NPE-150S2 | 120,000 BTU | 0.93 | 6.8 | 3.4 | No | 62 lb | Not listed |
Input, UEF, flow and weight from each model's page on navieninc.com; UEF matches ENERGY STAR's listings for the six NPE-2 models it certifies. Unit prices only, no installation. Prices change often.
Navien NPE-240S2: Best for Most Homes Without a Return Line
- Same burner and cabinet as the A2 for $389 less, with a slightly better UEF and 4 lb less weight.
- Navien rates it for 1/2-inch gas pipe up to 24 feet, subject to local code, which can save a gas-line upgrade on a retrofit.
- No built-in pump. It works with an external pump and the HotButton control on the front panel.
Navien NPE-240A2: Best If You Want Built-In Recirculation
- The buffer tank is aimed at the "cold water sandwich", and the pump cuts the wait at far fixtures, according to Navien's FAQ.
- Navien lists an optional minimum-flow setting under 0.01 GPM for the A2 in recirculation mode, against 0.5 GPM for the S2.
- ENERGY STAR estimates 178 therms a year, 2 more than the S2, before any recirculation run time.
Navien NPE-210S2: Best Value if Your Gas Supply Is Tight
- $111 less than the 240S2 for 0.5 GPM less at the federal test rise.
- Same 73 lb weight and cabinet, so it is a size-down, not a smaller install.
- A sensible choice when the gas meter or line can't feed 199,900 BTU without an upgrade.
Navien NPE-150S2: The New Small Model for Warm Climates
- The lightest NPE-2 at 62 lb, and the lowest gas input at 120,000 BTU.
- Its 0.93 UEF is the lowest in the S2 line; Navien estimates 120 therms a year for it, against 177 for the bigger S2 models.
- 3.4 GPM at a 67°F rise covers one shower plus a sink in a cold winter, so it suits small homes and warm groundwater.
Our pick for most buyers: the NPE-240S2. Go up to the NPE-240A2 only if you want recirculation and have no return line or pump today, because the pump is built in and covered by the same warranty. If you already have a return line and a pump, the S2 plus the existing pump on an aquastat is the cheaper route. Our recirculating pump guide covers external pumps, and the recirculation loop guide explains dedicated return lines versus crossover valves.
How the NPE-240S2 compares with the Rinnai RX199iN and Rheem IKONIC
These are the three 199,000 BTU condensing heaters most buyers compare. ENERGY STAR’s figures put them within 3 therms a year of each other, so the decision usually comes down to price, warranty terms and who will service the heater.
| Navien NPE-240S2 | Rinnai RX199iN | Rheem IKONIC ECOHS200iN | |
|---|---|---|---|
| UEF (ENERGY STAR) | 0.96 | 0.98 | 0.96 |
| GPM at 67°F rise (ENERGY STAR) | 5.8 | 5.8 | 5.8 |
| Gas use (ENERGY STAR) | 176 therms/yr | 173 therms/yr | 176 therms/yr |
| Built-in Wi-Fi | No (NaviLink add-on) | No (RWM200 module) | Yes (EcoNet) |
| Pump version | NPE-240A2 | RXP199iN | ECOHSR200iN (SR Series) |
| Heat exchanger | 15 yr (5 yr with uncontrolled recirculation) | 15 yr or 12,000 operating hours | 15 yr, includes full-unit replacement |
| Parts / labor | 5 yr / 1 yr | 5 yr / 5 yr if registered in 90 days (else 1 yr) | 5 yr / 1 yr |
| Online purchase | Voids the warranty, per Navien | Covered only from authorized e-tailers | Not stated on Rheem's product page |
| Price checked | $1,810.00 (SupplyStop, Nov 4) | $1,703.10 (SupplyStop, Oct 31) | Not checked (Home Depot blocks our price checks) |
ENERGY STAR certified water heaters database, checked November 4, 2026. Warranty terms from Navien's NPE-S2 warranty page, Rinnai's Sensei residential warranty and Rheem's IKONIC product pages. Rheem's IKONIC page also lists 2-inch PVC venting up to 70 feet and built-in EcoNet Wi-Fi.
Two differences matter more than the decimals. Labor coverage: Rinnai gives 5 years of labor if you register, while Navien and Rheem give 1 year, so a repair in year three is on you with the Navien. Where you buy: Navien’s terms are the strictest of the three, because they void the warranty for any internet purchase rather than only for unauthorized sellers. Our head-to-heads go deeper: Rinnai vs Navien and Navien vs Rheem.
The warranty fine print
Navien’s NPE-S2 warranty page lists the terms in a table and then a long list of exclusions. These are the ones that matter for a home install.
| Use | Heat exchanger | Parts | Labor |
|---|---|---|---|
| Residential, standard or controlled recirculation | 15 years | 5 years | 1 year |
| Residential, uncontrolled recirculation | 5 years | 3 years | 1 year |
| Commercial or combi, standard or controlled recirculation | 8 years | 5 years | 1 year |
| Commercial or combi, uncontrolled recirculation | 3 years | 3 years | 1 year |
- Internet purchases void it. Navien’s resale policy says consumer purchases “through the internet or other e-commerce channels shall void Navien’s warranty”. The same applies if your installer bought the heater from a supplier or distributor Navien hasn’t authorized.
- So does a non-licensed installer, and so does any install that doesn’t follow the installation manual or local code.
- “Uncontrolled” means a pump that runs all the time. Navien says an external pump circulating continuously through the heater falls under the uncontrolled terms, and an aquastat is the minimum control to keep the full 15 years.
- Scale isn’t covered. Damage from hard water deposits or lime build-up is excluded, which makes regular descaling part of keeping the warranty useful.
- The clock starts at installation, and Navien can ask for proof of the installation date. For new construction it starts when the buyer takes title.
- Moving the heater voids it, as does using an NPE-2 for space heating only.
- Claims go through the installer. Navien’s process is to contact the original installer first; its tech line (800-519-8794) is the fallback if the installer can’t be found.
One inconsistency to know about: Navien’s NPE-S2 FAQ page still carries answers written for the original NPE (one mentions a remote due “in late 2012”), and it says commercial use gets “10 years on the heat exchanger, 3 years on any other parts”. The current warranty table says 8 years and 5 years. The table is the document a claim would be judged against. The full brand-by-brand picture is in our tankless warranty guide.
Installation notes and what’s not in the box
| Item | When you need it | SupplyStop price, Nov 4, 2026 |
|---|---|---|
| 30025801A Outdoor Vent Kit, NPE-2 Series | Outdoor installs (Navien recommends outdoor mounting only in mild climates) | $79.95 |
| NaviLink Lite Wi-Fi controller (PBCMAS002) | App control for a single residential unit; mounts magnetically, no external power | $159.95 |
| NaviLink Wi-Fi control module (PBCM-AS-001) | App control on larger or cascaded systems | $219.90 |
| Plumb Easy 3-valve set, 3/4 in threaded (GXXX002140) | Isolation valves for flushing (see our isolation valve kit guide) | $189.00 |
| NaviCirc recirculation valve kit (30022965A) | Recirculation without a return line; external pump not included | $79.95 |
| 30027946B propane conversion kit | Replacement kit for the 240A2/240S2 (Navien's FAQ says conversion uses the kit supplied with the unit) | $11.95 |
- Gas line: Navien rates the NPE-S2 for 1/2-inch gas pipe up to 24 feet, “subject to local codes”. Its FAQ adds that the heater does not have to be the first appliance off the meter if the line is sized for it. Our gas line sizing guide shows when a half-inch run works.
- Venting: the product page lists 2-inch PVC up to 75 feet, with PVC, CPVC, polypropylene or stainless allowed and zero clearance to combustibles. The FAQ page still quotes 60 feet for 2-inch and 150 feet for 3-inch, so have the installer work from the current installation manual. See our venting guide.
- Propane conversion: the unit ships set for natural gas, and Navien says conversion must be done by a qualified service agency with the supplied kit. That matters: CPSC recall 19-057 in December 2018 covered about 3,400 first-generation NPE-180A, NPE-180S and NCB-180E units where the propane conversion could produce excess carbon monoxide. No injuries were reported, and no NPE-2 models were part of it.
- Condensate: as a condensing heater it needs a drain route; our condensate drain guide covers neutralizers and routing.
- Wi-Fi isn’t built in. ENERGY STAR lists the NPE-240S2 as not connected-capable on its own; app control needs a NaviLink controller.
- Outdoors in cold climates: Navien’s FAQ recommends outdoor mounting only in mild climates. Our freeze protection guide explains the risks during a power cut.
CPSC’s recall database lists two Navien recalls, checked November 4, 2026: the 2018 propane-conversion recall above, and a 2011 recall of about 13,000 T-Creator CR and CC heaters made in 2008, for a vent collar that could detach. Neither involves the current NPE-2 series.
Who should buy the NPE-240S2, and who shouldn’t
- Buy it if you’re replacing a gas tank or older tankless in a two- to three-bathroom home, don’t need recirculation, and have a licensed Navien installer who will supply the heater.
- Buy the NPE-240A2 instead if the far bathroom waits a long time for hot water and you have no return line or pump today.
- Buy the NPE-210S2 instead if your gas supply can’t support 199,900 BTU, or you live where groundwater stays above about 55°F.
- Look elsewhere if you want to buy the heater online and hire someone just to install it: Navien’s terms don’t cover that, while Rinnai covers purchases from its authorized e-tailers. Also look elsewhere if multi-year labor coverage matters to you; the Rinnai RX199iN gives 5 years of labor if registered. Our best gas tankless water heater guide ranks the alternatives, and the tankless water heater brands guide explains who makes what.
The bottom line
The Navien NPE-240S2 delivers the same 5.8 GPM at the federal test rise as the Rinnai RX199iN and Rheem IKONIC, a 0.96 UEF, natural gas or propane in one unit, and a 15-year heat-exchanger warranty, for $389 less than the pump-equipped NPE-240A2 at SupplyStop on November 4, 2026. Plan for 4.6 to 6.0 GPM of winter flow across most of the US, not 11.2, and budget for the isolation valves and, if you want them, an outdoor vent kit and NaviLink controller. The single biggest thing to get right is the purchase route: Navien’s warranty page says online purchases and non-licensed installers void the warranty, so have a licensed installer supply and fit it, keep any recirculation pump on a control, and keep the installation date on file.
Sources: Navien NPE-240S2, NPE-240A2, NPE-210S2, NPE-210A2, NPE-180S2, NPE-180A2 and NPE-150S2 product pages, NPE-S2 series page, NPE-S2 warranty page and NPE-S2 FAQ page (navieninc.com, November 4, 2026); ENERGY STAR certified water heaters database (data.energystar.gov, November 4, 2026); Rheem IKONIC S and SR Series product pages (rheem.com); Rinnai RX199iN data from our RX199iN review (October 31, 2026); prices from SupplyStop (November 4, 2026); CPSC recalls 12-074 and 19-057.