Top 10 Tankless Water Heaters — Best Overall + Best Value in 2027

1. Rinnai RX199iN Sensei

This ranks first because it pairs the category's best efficiency with near-top flow: 11.1 GPM at a 0.98 UEF, fed by up to 199,000 BTU of condensing natural-gas input. It mounts indoors or outdoors, vents through inexpensive PVC, and connects to the Rinnai Central app for scheduling and diagnostics. The heat exchanger carries a 15-year warranty, and with annual descaling plumbers expect 18 to 20 years of service at roughly $1,700.

Buy this if you have a gas line, multiple bathrooms, and expect two showers running at once. You trade away money: it costs about $250 more than the Navien NPE-240A2 and roughly $450 more than the A.O. Smith Signature Series, and it lacks the Navien's built-in recirculation pump. Hard-water households must commit to a yearly descaling flush or the flow and exchanger life both suffer.

2. Navien NPE-240A2

Second place goes to the only unit here with recirculation built into the box, eliminating the separate pump most homes bolt on. It delivers up to 11.2 GPM at a 35°F rise on a modulating 13,300 to 199,900 BTU burner, at a 0.95 UEF and ENERGY STAR rating. Dual stainless heat exchangers are rated up to 25 years — longer than any competitor's — and the price runs about $1,450.

This is the pick when a far-off master bath makes you wait 45 seconds for hot water. Against the Rinnai RX199iN above it, you give up three hundredths of UEF and the app polish, and gain a recirculation feature that would otherwise cost several hundred dollars installed. Budget for a condensate drain and venting run; the install is more involved than a simple swap.

3. EcoSmart ECO 27

Third because it is the cheapest genuine whole-home unit on this list at roughly $580 — under half the price of any gas pick above it. The 27 kW electric design supplies up to 6.6 GPM in warm climates, dropping to about 3 GPM against the coldest groundwater. Self-modulating control draws only the wattage the flow demands, copper and stainless internals resist scale, and the heating elements carry a lifetime warranty.

This fits Sun Belt homes with no gas service, where the venting, gas line, and combustion air of a Rinnai or Navien would add thousands to the install. The catch is electrical: it wants 200-amp service and heavy-gauge wiring, and a panel upgrade can erase the savings. Northern buyers should size up to the Rheem RTEX-36 below rather than accept the cold-water flow penalty.

4. Rheem RTEX-36

Fourth on the strength of serviceability: the 36 kW electric design uses replaceable heating elements and a digital thermostat, so most repairs are a screwdriver job instead of a service call. The extra 9 kW over the EcoSmart ECO 27 holds output steadier against cool incoming groundwater, and temperature sets in 1°F increments. At about $680 with Rheem's parts network behind it, the dollar-per-kilowatt math is strong.

Choose this over the ECO 27 if you live north of the warm-climate belt or simply want to fix the unit yourself. The 36 kW draw demands a serious panel — likely a full electrical upgrade — and it is overkill for a small condo or a mild coastal climate. It gives up the Stiebel Eltron's flow-control precision but costs about $135 less.

5. A.O. Smith Signature Series

Fifth because it delivers near-flagship gas output at a mid-tier price: up to 10.6 GPM on 180,000 to 199,000 BTU of condensing input for roughly $1,250. It runs on natural gas or propane, installs indoors or outdoors, and vents through standard PVC. The real differentiator is support — A.O. Smith's retailer and parts network is among the deepest in plumbing, so replacement components are stocked rather than special-ordered.

This suits large households that want high simultaneous flow without paying Rinnai flagship money. You lose about half a GPM against the RX199iN and Navien NPE-240A2, and the smart-app features are noticeably thinner than Rinnai Central. For owners who plan to hand the unit to a local plumber for service rather than manage it from a phone, that trade is easy.

6. Takagi T-H3-DV-N

Sixth because the value is extraordinary but the support horizon is not: around $500 buys a condensing indoor gas unit rated at 10 GPM on 199,000 BTU with ultra-low-NOx combustion. That is flagship-tier output for roughly a third of the Rinnai RX199iN's price. Takagi discontinued the line in December 2025, so current stock is closeout inventory — the specs are real, the factory backing is finite.

This makes sense for a landlord, a flip, or a DIY owner comfortable sourcing parts independently. Against the A.O. Smith above it, you save about $750 and lose half a GPM plus the deep parts network — a meaningful gap fifteen years out. Buyers who intend to keep the house for decades should pay up for a supported line instead.

7. Stiebel Eltron Tempra 36 Plus

Seventh for temperature stability rather than raw numbers: advanced flow control throttles output as demand shifts, so the shower does not spike or drop when a faucet opens elsewhere. It is a 36 kW whole-home electric unit rated at 7.03 GPM, German-engineered, silent, and vent-free. Stiebel Eltron backs it with a 10-year combined warranty, and street price runs about $815.

Pick this if inconsistent water temperature is the specific thing you hate about your current setup. It costs roughly $235 more than the EcoSmart ECO 27 and $135 more than the Rheem RTEX-36 for the same nominal wattage class, and the elements are not as owner-serviceable as the Rheem's. Like every 36 kW electric, it needs substantial panel capacity before it is even a candidate.

8. Rinnai RX130iN Sensei

Eighth because it is the correctly sized version of the winner for homes that will never use 11 GPM. The condensing gas platform, Rinnai Central app control, PVC venting, and build quality all carry over from the RX199iN, but output is scaled to one or two simultaneous fixtures. At roughly $1,150 it undercuts the flagship by about $550 while keeping the reliability record that put Rinnai at the top of this list.

A couple or a two-bath household gets the brand without paying for capacity that sits idle. The limit is real: add a third bathroom or run laundry during a shower and this unit will disappoint where the RX199iN would not. Annual descaling is still mandatory in hard water, and the A.O. Smith Signature Series offers far more flow for about $100 less.

9. EcoSmart ECO 11

Ninth because it solves a different problem than everything above it: a 13 kW, 240-volt point-of-use unit rated at 2.54 GPM, installed at the fixture rather than in the utility room. Self-modulating copper immersion elements reach up to 0.96 UEF, and the wall footprint is small enough for a vanity cabinet or a garage stud bay. Wiring requires a double-pole 60-amp breaker and 6-gauge cable, and the unit runs about $230.

This is for a workshop sink, a garage bath, or a far-corner shower where the main heater takes a minute to arrive. It cannot serve a house — 2.54 GPM covers one shower or a sink, full stop. Compared with the Bosch Tronic 3000 below, it costs $70 more but actually handles a shower, not just handwashing.

10. Bosch Tronic 3000 US3-2R

Tenth because its 3.6 kW output is the smallest here, but at roughly $160 it is also the cheapest and simplest install on the list. The compact body fits behind a bathroom vanity and eliminates the cold-water lag at a single lavatory faucet. Electrical demand is modest compared with the 36 kW whole-home electrics, which keeps it inside most existing panels without an upgrade.

Use it for handwashing duty at a sink far from the water heater — a powder room, a basement utility sink, an office bath. It will not run a shower and will not serve two fixtures; that is the EcoSmart ECO 11's job for $70 more. If the fixture in question ever needs real volume, skip this tier entirely and size a whole-home unit.

How we ranked these

We weighted flow rate and capacity heaviest at 25 percent, because a heater that cannot run two showers is the wrong heater regardless of efficiency. Energy efficiency, measured as UEF and condensing heat recovery, took 20 percent. Gas-versus-electric fit, reliability and warranty, and install and venting each carried 15 percent. Price-to-performance closed at 10 percent. GPM, UEF, and BTU claims were cross-checked against Rinnai, Navien, Rheem, EcoSmart, and Stiebel Eltron spec sheets.

We ignored app dashboards, voice-assistant tie-ins, and efficiency claims separated by a few hundredths of a UEF point, because neither changes a fuel bill or a shower. We ignored retailer star ratings, which conflate shipping damage and bad installs with product quality. And we ignored installed-price quotes entirely — labor swings by region, gas-line size, and panel capacity, so a national install number would mislead more than it helps.

What to look for

Size for your coldest incoming water, not the average. A 70-degree rise in January cuts usable flow roughly in half, which is why the EcoSmart ECO 27 delivers 6.6 GPM in Florida and closer to 3 GPM in Minnesota. Add up the fixtures you actually run at once — two showers plus a kitchen sink is roughly 6 to 9 GPM. Then confirm your panel or gas line supports it.

The common mistake is buying the box and ignoring the install. A 36 kW electric like the Rheem RTEX-36 can force a 200-amp panel upgrade that costs more than the heater; a gas unit may need a larger supply line and a condensate drain. The second mistake is skipping annual descaling — scale kills flow and heat exchangers faster than any brand difference on this list.

Related questions

What size tankless water heater do I need for a three-bathroom house?

Count simultaneous fixtures, then multiply by your temperature rise. Three baths that might run two showers and a sink together need 8 to 11 GPM, which puts you in gas territory — the Rinnai RX199iN at 11.1 GPM or the Navien NPE-240A2 at 11.2 GPM. Electric whole-home units rarely sustain that flow once groundwater drops below 60 degrees.

Will a tankless water heater actually lower my utility bill?

Modestly. Condensing gas units at 0.95 to 0.98 UEF eliminate the standby loss of keeping 50 gallons hot around the clock, which typically saves a meaningful but not dramatic slice of the water-heating line item. The bigger wins are unlimited hot water, a near-20-year service life versus 10 to 12 for a tank, and reclaimed floor space.

Why does my tankless heater send a cold slug mid-shower?

That is the cold-water sandwich: the burner shuts off when you briefly close the tap, and the cooled water sitting in the exchanger reaches you before the reheated water does. Built-in recirculation, like the Navien NPE-240A2 offers, largely eliminates it. Advanced flow control on the Stiebel Eltron Tempra 36 Plus addresses the electric version of the same complaint.

Can I install a tankless water heater myself?

A point-of-use unit like the Bosch Tronic 3000 is genuinely DIY if you are comfortable with a supply line and a small circuit. Whole-home units are not. Gas models need combustion air, PVC venting, a condensate drain, and gas sizing; whole-home electrics need 200-amp service and heavy-gauge wire. Both usually require permits and inspection, and bad installs void warranties.

Do I need a water softener with a tankless heater?

Not required, but hardness above roughly 7 grains per gallon makes one worth pricing. Scale coats the heat exchanger, chokes flow, and forces the burner to work harder, which is the leading cause of premature failure. If you skip the softener, commit to an annual descaling flush — that alone protects most of the unit's rated lifespan.

Is built-in recirculation worth paying extra for?

If your master bath sits far from the heater and you currently waste 30 seconds of cold water every morning, yes. Built-in recirculation on the Navien NPE-240A2 avoids buying and wiring a separate pump and dedicated return line. If your fixtures are clustered near the unit, the wait is already short and the feature earns little.

What does a tankless water heater actually cost installed?

The unit is often the smaller number. Prices here run $160 for the Bosch under-sink booster to $1,700 for the Rinnai flagship, but a gas retrofit adding venting, a larger gas line, and a condensate drain frequently matches or exceeds the equipment cost. Electric whole-home installs hinge on whether your panel already has capacity.

Should I choose a point-of-use unit instead of upgrading the whole house?

Sometimes. If one remote fixture is the only real problem — a garage sink, a workshop, a far-corner bath — a $230 EcoSmart ECO 11 or $160 Bosch Tronic 3000 solves it for a fraction of a whole-home swap. Upgrade the main heater only when capacity or age is the actual complaint.

FAQ

How many GPM do I need for a whole house?

A typical family running two showers, or a shower plus the kitchen, wants 6 to 9 GPM. Homes with multiple simultaneous bathrooms should target 10 to 11-plus GPM. Size for your coldest incoming water, since a larger temperature rise directly reduces usable flow — the same unit that hits 6.6 GPM in a warm climate may deliver half that in winter.

Is gas or electric tankless better?

Gas delivers higher flow for whole-home use and holds up in cold climates, but requires a gas line, venting, and a condensate drain. Electric costs less to buy, installs without venting, and fits tight spaces, but caps out at lower flow and may demand a 200-amp panel upgrade. Match fuel to your existing infrastructure first, then compare models.

What does condensing mean, and is it worth the premium?

A condensing unit captures heat from exhaust gases that a standard unit throws away, pushing efficiency to 0.95 to 0.98 UEF. It costs more up front but vents through inexpensive PVC instead of stainless, which often offsets part of the difference at install. In cold regions with high gas use, the fuel savings make it the clear default.

How long do tankless water heaters last?

With annual descaling, quality condensing gas units like the Rinnai RX199iN Sensei run 18 to 20 years, and dual stainless heat exchangers such as Navien's are rated up to 25. That is roughly double a conventional tank's 10 to 12 years. Skip the descaling in hard water and you can lose a third of that lifespan.

Do I really need to descale it every year?

In hard-water areas, yes. Scale buildup narrows the heat exchanger passages, drops flow, and forces longer burner cycles that accelerate failure. A vinegar or commercial descaler flush takes under an hour with a small pump and two hoses. It is the single highest-return maintenance task on the unit and is often a warranty condition.

Can a point-of-use unit replace my whole-home heater?

No. The EcoSmart ECO 11 at 2.54 GPM and the Bosch Tronic 3000 at 3.6 kW are built to serve one or two fixtures. The Bosch is a handwashing booster and will not run a shower. Use these to add fast hot water at a remote sink or bath, never as the house's primary supply.

Why is the Rinnai RX199iN Sensei the Best Overall pick?

It combines the highest practical flow on this list at 11.1 GPM with a class-leading 0.98 UEF, up to 199,000 BTU of input, indoor or outdoor installation on cheap PVC venting, app-based scheduling and diagnostics, and a 15-year heat-exchanger warranty. Nothing else here matches that combination of flow, efficiency, and expected service life in a single box.

Why is the EcoSmart ECO 27 the Best Value pick?

At roughly $580, this 27 kW electric supplies whole-home hot water with no gas line, no venting, and no combustion air requirement — the three things that make gas retrofits expensive. Self-modulating elements draw only the power needed, and the elements carry a lifetime warranty. The catch is a 200-amp panel and a sharp flow drop in cold-groundwater regions.

Does the Takagi T-H3-DV-N being discontinued matter?

It depends on your risk tolerance. The unit itself is a legitimate 10 GPM, 199,000 BTU condensing gas heater with ultra-low-NOx combustion at about $500, which is remarkable value. But the line ended in December 2025, so remaining stock is closeout and long-term factory parts support is uncertain. Buy it for price, not for decades of warranty backing.

Will a tankless water heater work during a power outage?

Generally no. Electric models obviously stop, and modern condensing gas units still need power for the ignition, control board, and combustion fan, so they shut down too. If outages are common where you live, plan on a generator circuit for the heater or accept cold water — this is one area where an older tank held an advantage.

Sources

• https://www.energy.gov/energysaver/tankless-or-demand-type-water-heaters
• https://www.energystar.gov/products/water_heaters/tankless_water_heaters
• https://www.rheem.com/product/rheem-professional-classic-series-tankless-electric-rtex-36-kw-rtex-36-208v-performance/
• https://www.ecosmartus.com/product/ecosmart-ECO-27-27-kW-Electric-Tankless-Water-Heater
• https://www.rinnai.us/residential/product-detail/rx130in
• https://www.homedepot.com/p/Stiebel-Eltron-Tempra-36-Plus-Advanced-Flow-Control-and-Self-Modulating-36-kW-7-03-GPM-Residential-Electric-Tankless-Water-Heater-Tempra-36-Plus/306745514
• https://www.lowes.com/pd/A-O-Smith-Signature-Premier-10-GPM-199000-BTU-Indoor-Natural-Gas-Tankless-Water-Heater/1000550129
• https://www.consumerreports.org/appliances/water-heaters/
• https://www.thisoldhouse.com/plumbing/reviews/best-tankless-water-heaters
• https://www.bobvila.com/articles/best-tankless-water-heater/

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