Best Tankless Water Heater Brands (Compared, 2026)

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Quick answer from a licensed plumber: No brand wins on flow. At a 45°F rise the 199,000-class gas units from Navien, Rinnai, Noritz and Rheem list 8.5 to 8.8 GPM in their own documents, while the headline maximums use different bases and cannot be compared. The real differences are built-in recirculation, warranty conditions, and where the maker lets you buy: Navien voids its warranty on internet purchases, Noritz on purchases from a seller it has not authorized, and Takagi sells only through wholesalers and contractors.

Our take: want a condensing gas unit sold by Amazon? The Rheem RTGH-84DVLN-3: Check the Rheem RTGH-84DVLN-3 on Amazon. Want a 199,000 BTU/h condensing unit from a seller whose name matches Rinnai’s authorized list? The Rinnai RX199iN: Check the Rinnai RX199iN on Amazon. No gas line? The Stiebel Eltron Tempra 24 Trend, if your panel can carry it: Check the Stiebel Eltron Tempra 24 Trend on Amazon.

This guide compares nine brands from their own manuals, spec sheets and warranty documents: Rinnai, Navien, Rheem, Noritz, Takagi and A. O. Smith for gas, and Stiebel Eltron, Bosch and EcoSmart for electric. To pick a model by fuel, see our best tankless water heater guide, best gas, best electric and best propane guides.

Tankless Brands Side by Side

Brand	Residential lines (maker sites)	Condensing or not	Built-in recirculation pump	Residential warranty: heat exchanger / parts / labor
Rinnai	SENSEI RX and RXP; RUS and RUCS; RE, REP and V	RX, RXP, RUS, RUCS condensing; RE, REP, V non-condensing	RXP and REP	15 yr (or 12,000 hours) / 5 yr / 1 yr, or 5 yr labor if registered
Navien	NPE-A2 and NPE-S2	Condensing	NPE-A2 (plus a 0.5-gallon buffer tank)	15 yr / 5 yr / 1 yr (standard or controlled recirculation)
Rheem	RTGH; IKONIC S and SR; RTG; RTG-R	RTGH and IKONIC condensing; RTG and RTG-R non-condensing	IKONIC SR and RTG-R	15 yr / 5 yr / 1 yr; IKONIC page: 15 yr with registration, 12 yr without
Noritz	EZ Series (EZ98, EZ111); NRCR Pro (NRCR92, NRCR111); NRCB combi boiler	EZ and NRCR: condensing	NRCR	EZ: 25 yr (or 15,000 hours); NRCR: 15 yr (or 12,000 hours); parts 5 yr, labor 1 yr
Takagi	TK-X3P; TK-540X3; TK-540P; TK-510C, 310C, 110C; TK-510U, 310U, 110U	X3P, 540X3, 540P condensing; C and U series non-condensing	TK-X3P and TK-540P	15 yr / 5 yr / 1 yr; the TK-540P also needs fewer than 9,000 operating hours
A. O. Smith	Adapt+ (Premium), Adapt SC (Standard), Adapt NC	Adapt+ and SC condensing; NC non-condensing	Adapt+ only, per A. O. Smith	15 yr / 5 yr / 1 yr

Lines are from each maker’s own site and documents as of September 29, 2026; check the model number you are buying. Condensing units vent in plastic and need a condensate drain. Vent material rules differ by maker, so follow the manual for your exact model.

Flow on the Same Basis: a 45°F Rise

Makers state their headline flow on different bases, so those numbers cannot be lined up. Navien, Rinnai and Rheem quote a 35°F rise, Noritz a 30°F rise, and Takagi and A. O. Smith state a maximum with no rise. The table shows each maker’s own figure at 45°F and 67°F rise where one is published. A 45°F rise is a 120°F setting with 75°F incoming water (our arithmetic). Colder water means a bigger rise and less flow.

199,000-class gas unit	Maker’s stated maximum flow	GPM at a 45°F rise	GPM at a 67°F rise
Navien NPE-240A2	11.2 GPM at a 35°F rise	8.7	5.6
Rinnai RX199iN / RXP199iN	11.1 GPM at a 35°F rise	8.6	5.8
Noritz EZ111	11.1 GPM at a 30°F rise	8.7	not listed (60°F: 6.5; 70°F: 5.6)
Rheem IKONIC RTGH-S11i / SR11i	11.2 GPM at a 35°F rise	8.8	5.9
Rheem RTGH-95DVELN-3	9.5 GPM at a 35°F rise	8.5	5.7
A. O. Smith ATHR-199X3	10.5 GPM (no rise stated)	not listed	5.9 (product page)
Takagi 199X3P (TK-X3P)	10.0 GPM (no rise stated)	not listed; output-temperature graphs only	not listed

Navien, Rinnai, Noritz and Rheem’s IKONIC list 8.6 to 8.8 GPM at a 45°F rise, and Rheem’s RTGH-95 lists 8.5. That is a spread of 0.3 GPM (our arithmetic), so flow does not separate these brands. At a 67°F rise, the makers that publish a figure list 5.6 (Navien) to 5.9 GPM (Rheem IKONIC, A. O. Smith); Noritz’s table skips 67°F. Takagi lists output-temperature graphs, not GPM by rise, so we cannot place it. Our size calculator turns your fixtures into a required flow.

Warranty Fine Print by Brand

Headline years look alike. The conditions do not. Quotes are short pieces of each maker’s own wording.

Brand	What starts the clock	Registration	Where you buy	Who must install
Navien	Date of original installation; proof required	FAQ: tech support cannot send parts without a registered product	Warranty void for a product “purchased through the internet, other e-commerce channels,” or through an installer who got it from a supplier Navien has not authorized	Void if “installed by a non-licensed installer”; manual: only a licensed professional connects gas
Rinnai	Date of purchase (warranty document); proof is a dated receipt or registration within 30 days of purchase	5-year labor if registered within 90 days: of purchase on the website, of installation in the warranty document; otherwise 1 year	A product from an unauthorized PRO is not covered; unauthorized online dealers “do not carry a warranty from Rinnai”	A trained professional who attended a Rinnai class is “recommended” (older manuals said “required”; all warranties are honored as written); manual: trained and qualified professional
Rheem	Install date if documented; otherwise manufacture date plus 90 days	IKONIC: 15 years “w/ registration,” 12 years “w/o registration”; no window is stated in the pages we read	Certificate names no seller condition; the online sales policy is a reseller rule	Certificate “strongly recommends” a licensed, state-qualified, trained contractor; labor covered only for service by one
Noritz	Proper installation date or 30 days after purchase, whichever is first; install date and receipt copy required; original buyer only, ends if ownership transfers	Online form at noritz.com/warranty; the card’s terms do not state a deadline	Product from a seller “not authorized by Noritz” is not covered; the site says buy through a plumbing professional	Installed “by a method recognized and authorized by Noritz”; manual: qualified installer
Takagi	Original retail buyer only; proof of purchase and install date required at claim	No registration window in the warranty documents	About page: sold exclusively by plumbing wholesalers and contractors	Not covered if “not installed by a licensed plumber, gas installer, or contractor”
A. O. Smith	Date of original installation; if no proof, 60 days after manufacture; covers later owners at the original site	No registration window in the warranty sheet	No seller condition in the warranty sheet we read	Not covered if “not installed by a licensed plumber, gas installer, or contractor”

Rinnai’s heat exchanger term also stops at 12,000 operating hours, Noritz’s EZ term at 15,000 and the Takagi TK-540P’s at 9,000, and Rheem’s certificate says “All warranties void after 12,000 hours of operation.” Water quality is a second set of conditions. Navien, Rinnai, Noritz and Rheem all list total hardness up to 200 mg/L (12 grains per gallon). Takagi’s 540P-era warranty caps it at 7 grains; its X3 warranty lists no hardness limit but excludes pH outside 6.5 to 8.5 and iron above 0.3 mg/L. A. O. Smith keeps 15-year coverage for scale failures on X3 models in hard water, not on M models. Test your water first.

Brand by Brand

Rinnai

Rinnai’s documents disagree on the RX199 maximum (11.0 GPM in the spec sheet, 11.1 in the brochure) and on the registration window. Registering as soon as the heater is installed, and within 30 days of purchase, satisfies both readings. The warranty document also cuts the heat exchanger to 8 years or 12,000 hours if the setting exceeds 160°F.

Rheem

For indoor direct-vent installs, Rheem’s RTG spec sheet lists Category III stainless steel or Rheem-approved vent materials for the non-condensing units. The IKONIC page splits the heat exchanger term by registration, 15 years against 12, but no Rheem document we read gives a deadline, so register at install.

Noritz

Noritz’s 2025 warranty card has the longest term here (25 years on the EZ in a single-family home, for the original buyer only) and an explicit seller rule. Noritz’s EZ page lists an 18,000–180,000 BTU input for the EZ111, while its spec sheet lists 18,000–199,900; we use the spec sheet. Noritz says it does not sell to consumers directly. Its IMAP page lists Build.com, Hajoca Corporation (via Amazon) and Plumbing-deals.com as preferred e-commerce vendors. Its warranty web page also shows older terms, so use the 2025 card.

Takagi

Takagi’s newest condensing line is the TK-X3P (160,000, 180,000 and 199,000 BTU/h, integrated pump) with built-in X3 scale prevention. Its X3P warranty cuts heat exchanger and parts coverage to 3 years when a pump has no control (aquastat or timer), and excludes an application that fires the heater more than 300 times a day.

A. O. Smith

A. O. Smith’s current gas tankless family is Adapt+ (a single stainless heat exchanger, integrated pump), Adapt SC and Adapt NC. Its older ProLine XE ATI-540H page is marked discontinued. Its marketing claims “no exclusions for hard water,” but the warranty sheet limits that to X3 models.

Electric brands: Stiebel Eltron, Bosch and EcoSmart

Electric units need no vent or gas line, but the load is large: the Tempra 24 needs 2 x 50 A breakers, the Bosch 6100 C 27 kW needs 3 x 40 A, and the EcoSmart ECOS 27 needs 3 x 40 A breakers, and its spec sheet recommends 200 A service. Bosch’s gas tankless models now appear on its discontinued-products page.

Electric brand	Whole-house line	Warranty	Flow near a 45°F rise
Stiebel Eltron	Tempra Trend and Tempra Plus (12 to 36 kW)	7 yr leaks, 3 yr failures, from date of purchase	Tempra 29 (28.8 kW, 240 V): 4.36 GPM at a 46°F rise (105°F out, 59°F in); Tempra 24: 3.63
Bosch	Tronic 6100 C (18 and 27 kW); Tronic 4000 C is point-of-use	Heating canister 5 yr, other parts 2 yr, from installation	Tronic 6100 C 27 kW: 4.09 GPM at 45°F; 18 kW: 2.73
EcoSmart (a Rheem brand)	ECOS 12, 18 and 27; ECO and POU models	5 yr leaks, 1 yr parts, from original purchase	ECOS 27: 4.3 GPM at a 43°F rise and 3.8 at 48°F (105°F set point, 62°F and 57°F ground water)

Rises in the last column differ by a few degrees between makers, so treat those figures as close, not equal. Stiebel’s manual says a licensed electrician and plumber must install the unit, EcoSmart’s says a qualified electrician and plumber should, and Bosch’s warranty covers a heater a qualified service contractor installs and maintains. Our three Amazon links follow.

Condensing Gas, Sold by Amazon

Rheem RTGH-84DVLN-3 Condensing Gas Tankless Water Heater

Natural gas · 157,000 BTU/h maximum, 11,000 minimum · 8.4 GPM at a 35°F rise, 6.7 at 45°F, 4.6 at 67°F · 2-inch vent to 60 ft or 3-inch to 150 ft of straight pipe, 6 ft less per 90° elbow · Schedule 40 PVC, CPVC or polypropylene · 120 V · 52.9 lb · 15-year heat exchanger, 5-year parts, 1-year labor

At 157,000 BTU/h the RTGH-84DVLN-3 is smaller than the 199,000-class units in the flow table above; Rheem sizes it for three bathrooms. It is condensing, so it vents in plastic and needs a condensate drain. Rheem’s spec sheet lists no built-in recirculation pump for it; the pump versions are the IKONIC SR and RTG-R lines.

Rheem’s Water Heater Online Sales Policy (effective January 1, 2022) is a rule for its distributors and resellers. It says Rheem water heaters may not be sold on online marketplaces, “including but not limited to Amazon Marketplace,” unless Rheem agrees in writing, and it reserves Rheem’s right to sell online “through other programs.” This listing is sold by Amazon.com itself, and we cannot see from Amazon how Rheem supplies it. The policy is not a warranty term: Rheem’s warranty certificate names no purchase-channel condition, but the owner must show proof of purchase or ownership to make a claim. Keep the receipt and register the serial number.

Condensing: plastic vent, 2-inch to 60 ft or 3-inch to 150 ft of straight pipe, per Rheem
Rheem lists flow at 35, 45 and 67°F, so you can size it on your own rise
Rheem lists 1/2-inch gas line compatibility up to 24 ft, subject to local code

No built-in recirculation pump is listed for this model
Rheem’s reseller policy restricts marketplace sales without its written consent; we cannot see how Amazon sources this unit
Rheem strongly recommends a licensed, state-qualified, trained contractor, and pays labor only for service by one
The certificate says “All warranties void after 12,000 hours of operation.”

Verdict: The pick if you want a condensing gas unit sold by Amazon, will use a licensed installer, and will register the serial number and keep the receipt.

Check the Rheem RTGH-84DVLN-3 on Amazon

Bigger Condensing Unit, UEF 0.98

Rinnai SENSEI RX199iN Condensing Gas Tankless Water Heater

Natural gas or propane, set in the controller menu · 15,000–199,000 BTU/h · 11.1 GPM at a 35°F rise, 8.6 at 45°F, 6.5 at 60°F per Rinnai’s brochure · UEF 0.98 · 120 V · 55 lb · 3/4-inch NPT gas, hot and cold · 2- or 3-inch PVC, CPVC or polypropylene vent · 15-year heat exchanger (or 12,000 hours), 5-year parts, labor 1 year or 5 if registered

The RX199iN is Rinnai’s condensing whole-house unit without a pump. The RXP models add an internal pump, at the same flow. For a full head-to-head with Navien, see our Navien vs Rinnai comparison.

Rinnai’s warranty page says products from unauthorized online dealers “do not carry a warranty from Rinnai.” Its authorized e-tailer list includes bigfrogsupply.com and efaucets.com and allows sales through Amazon. On 10/3/2026 the RX199iN listing was In Stock from eFaucets, a third-party seller whose name matches that list; Amazon does not verify the match, so confirm it at checkout. This is our third-party exception: no Rinnai unit we checked was sold by Amazon or Rinnai, and brand and model are confirmed from Amazon’s listing data.

8.6 GPM at a 45°F rise per Rinnai, against 6.7 for the Rheem RTGH-84 above
Natural gas or propane is selected in the controller menu within 20 minutes of power-up, and a supplied label marks propane, per Rinnai’s manual
Rinnai publishes an authorized online seller list and allows it to sell through Amazon

The linked listing is from a third-party seller, not Rinnai or Amazon
No recirculation pump on the RX199iN; the RXP adds one
Rinnai’s website and its warranty document disagree on whether the 90-day registration window for 5-year labor runs from purchase or from installation

Verdict: The pick if you want more flow than the Rheem RTGH-84 (8.6 against 6.7 GPM at a 45°F rise, per each maker), will buy from a seller whose name matches Rinnai’s authorized list (check it at checkout), and will pay a trained pro to install it.

Check the Rinnai RX199iN on Amazon

Electric Whole-House Option

Stiebel Eltron Tempra 24 Trend Electric Tankless Water Heater

24 kW · 240 V · 2 x 50 A double-pole breakers and 2 x 8/2 AWG copper · 150 A main service recommended · no venting or gas · 3/4-inch NPT · 16.1 lb · UEF 0.97 · leak warranty 7 years, failure warranty 3 years from date of purchase

Stiebel’s flow table is by inlet and outlet temperature. For the 24 kW at 240 V with 105°F out, it lists 3.63 GPM at 59°F in (a 46°F rise, our arithmetic), 6.05 GPM at 77°F in, and 2.52 GPM at 39°F in (a 66°F rise). Check the table for your coldest month.

Stiebel’s warranty runs from the date of purchase to the original purchaser and needs proof of purchase with a date; without one, coverage starts from the manufacture date. It lists hard water as an exclusion. The installation manual says the unit must be installed by a licensed electrician and plumber. The listing was In Stock and sold by Amazon.

7-year leak and 3-year failure warranty from date of purchase, per Stiebel Eltron
No venting, gas line or condensate drain
Flow table covers inlet temperatures from 39°F to 131°F at three outlet settings

The 24 kW model needs 2 x 50 A breakers, and Stiebel recommends 150 A main service
Flow is 2.52 GPM at 39°F inlet to 105°F out (24 kW, 240 V)
Hard water damage is excluded and proof of the purchase date is required

Verdict: The pick for a home with no gas, a warm or mild climate, and a panel that can carry it. Have an electrician confirm the panel first.

Check the Stiebel Eltron Tempra 24 Trend on Amazon

I send an occasional note when a new guide goes up — repairs worth doing yourself, and the parts that actually last. No spam, no course funnel; written by a licensed Georgia plumber.

Before You Buy

Pick the fuel first. Gas needs a gas line and a vent; electric needs a large electrical service. Propane is a separate model for most makers; see our propane guide.
Size on your own rise, not the headline number. Electric units lose flow fast in cold ground water.
Have the gas line sized by a gas fitter. A 199,900 BTU/h heater burns about 200 cubic feet of natural gas per hour at 1,000 BTU per cubic foot (our arithmetic), on top of every other gas appliance. Navien lists 1/2-inch gas pipe up to 24 feet equivalent length, and Rheem lists 1/2-inch compatibility up to 24 feet, subject to local code. A. O. Smith’s Adapt+ spec sheet lists a 1/2-inch gas line or larger. Noritz’s EZ spec sheet says “Compatible with 1/2” gas pipe – see installation manual.”
Plan the condensate. Condensing units produce acidic condensate. Check local code on where it may drain.
Decide on recirculation now. The FAQ lists the pump models. Our installation cost guide covers what changes the job.

Who Should Install It

Gas tankless installs involve gas piping, venting and condensate; the table above shows what each maker requires of the installer, and Navien, Takagi and A. O. Smith exclude units not installed by a licensed installer. Ask your building department about a permit. If you ever smell gas, Rheem’s and Navien’s manuals give the same steps: do not light any appliance or touch any electrical switch, and call your gas supplier from a neighbor’s phone, or the fire department if you cannot reach the supplier. Afterward, register the heater and keep these handy: Rheem, Rinnai and Navien NPE-A2. Also see our descaling guide.

FAQ

Which tankless water heater brand is the most reliable?

No maker publishes failure rates, and we did not test any unit. What you can compare is the paper. Rinnai, Navien, Rheem, Takagi and A. O. Smith all list a 15-year heat exchanger for a residential install. Noritz lists 25 years on its EZ Series in a single-family home, for the original buyer only. The conditions attached to those years differ; see the table above.

Which tankless brands have a built-in recirculation pump?

Navien NPE-A2 (pump plus a 0.5-gallon buffer tank), Rinnai RXP and REP, Rheem IKONIC SR and RTG-R, Noritz NRCR, Takagi TK-X3P and TK-540P, and A. O. Smith Adapt+, per each maker’s documents. Navien, Rheem, Noritz, Takagi and A. O. Smith shorten warranty terms if a pump runs with no control such as an aquastat or timer. For Navien against Rinnai in detail, see our Navien vs Rinnai guide.

Can I buy a tankless water heater online and keep the warranty?

It depends on the maker. Navien voids its warranty on internet and e-commerce purchases. Noritz does not cover a product from a seller it has not authorized. Rinnai says unauthorized online dealers carry no Rinnai warranty. Takagi says it sells only through wholesalers and contractors. Rheem, A. O. Smith, Stiebel Eltron, Bosch and EcoSmart name no purchase-channel condition in the warranty documents we read. Ask the maker before you order.

Are Takagi and A. O. Smith the same company?

They are related. Takagi’s TK-510C spec sheet lists its copyright as “Takagi – A. O. Smith Tankless Water Heater Company LLC,” and both makers’ warranty sheets carry the same Ashland City, Tennessee address. Adapt+ and TK-X3P share sizes and an integrated pump, but the spec sheets differ (10.5 GPM maximum against 10.0). We found no maker statement that they are the same unit.

Is EcoSmart the same as Rheem?

EcoSmart’s ECOS spec sheet says EcoSmart is a member of the Rheem family of brands. For the ECOS electric models it lists 5 years on leaks and 1 year on parts, from the date of original purchase. See our best electric guide.

Why Trust Plumbing Picks

Plumbing Picks is written by a licensed Georgia journeyman plumber. Every spec here comes from the maker documents listed below, which we opened and read, or from the Amazon listings we link; nothing comes from hands-on testing. On September 29, 2026 the Rheem and Stiebel Eltron listings were In Stock and sold by Amazon. We normally link only units sold or shipped by Amazon or the maker; no Rinnai unit was, so we link a genuine-model listing from a seller whose name matches Rinnai’s authorized list. We did not link Navien (no heater on Amazon, parts only), Noritz (no Noritz heater was sold by a vendor on Noritz’s preferred e-commerce list), Takagi (third-party, older models), A. O. Smith (third-party, too few in stock), EcoSmart (low on stock) or Bosch (listing text described a different product). If you buy through a link we may earn a commission at no extra cost to you. Nobody pays to be included here. More on who writes this and how we pick.

Sources

Bottom Line

Pick the fuel, size the heater on your own temperature rise, then compare brands on the fine print. Flow is a tie among the big gas makers at a 45°F rise. Recirculation and buying rules are not. Use a licensed installer, register the serial number, and keep the receipt.