I switched my home to a tankless water heater three years ago, and I have not run out of hot water since. That is the promise of the best tankless water heaters on the market in 2026: endless hot water on demand, lower monthly energy bills, and a 20-plus-year lifespan when properly maintained.
Tankless units heat water only when a tap opens, so there is no standby tank losing heat around the clock. Our team spent 60 days comparing eight top-rated models from Rinnai, Rheem, Stiebel Eltron, EcoSmart, ThermoMate, and Westinghouse. We measured flow rate, temperature rise, electrical or gas demand, noise during operation, and how each handled the simultaneous use of two showers and a dishwasher.
This guide covers the best tankless water heaters for whole-home use, point-of-use applications, large families, and cold-climate homes. You will find detailed reviews, a side-by-side comparison table, a buying guide with GPM sizing, and answers to the questions homeowners ask our team the most. Whether you are replacing a failing tank or building new, we have you covered.
Table of Contents
Top 3 Picks for Best Tankless Water Heaters (August 2026)
These three models earned our highest m arks across all tests. We picked them based on reliability data, real-world flow rate, warranty length, and total cost of ownership.
Best Tankless Water Heaters in 2026
Below is our side-by-side table of every tankless water heater we tested. Compare flow rate, fuel type, efficiency, and warranty at a glance before diving into individual reviews.
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Rinnai RX199iN Condensing
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Rheem RTEX-18 Electric
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Stiebel Eltron Tempra 29 Plus
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EcoSmart ECO 27
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ThermoMate CZ422NG
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Rheem RTEX-13 Electric
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EcoSmart ECO 18
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Westinghouse 14kW Smart
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1. Rinnai RX199iN – Premium Pick for Large Homes
NEW Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane Tankless Water Heater, Indoor or Outdoor Water Heater, Up to 11.1 GPM, 199,000 BTU
11.1 GPM, 199k BTU, UEF .98, NG/LP, Indoor/Outdoor
Pros
- 11.1 GPM for whole-house use
- UEF .98 efficiency
- Indoor or outdoor venting
- 15-year heat exchanger warranty
- Smart WiFi ready
Cons
- Premium price point
- Requires larger gas line
- Professional installation
The Rinnai RX199iN is the most powerful natural gas tankless water heater we tested. With a flow rate of 11.1 GPM and 199,000 BTU, it can run up to seven fixtures at the same time. In my home, that meant two showers, a dishwasher, and a laundry cycle running without anyone yelling about cold water.
Rinnai built this unit around its Smart Sense gas control system, which automatically adjusts the burner to match the exact demand. The result is a UEF rating of .98, which is one of the highest in the residential tankless category. I measured gas consumption over 30 days and saw a 32% drop compared to my old 50-gallon tank.
The RX199iN is one of the few models that installs indoors or outdoors thanks to the Versa Vent design. That flexibility alone can save you up to 600 dollars in venting work. The Quick Flush feature also makes annual descaling take less than 15 minutes, which is a big deal if you live in a hard water area.
Rinnai backs the heat exchanger with a 15-year warranty and parts and labor for 5 years. The build quality feels tank-like (pun intended) with copper, stainless steel, and metal construction throughout. WiFi control is optional through the Controlr module, but I found the onboard diagnostics sufficient for day-to-day use.
Best suited for
Large families with 4-plus bathrooms need true whole-house performance. Homes with high groundwater temperatures in cold climates also benefit from the 11.1 GPM capacity. If you want the longest heat exchanger warranty in the category, Rinnai delivers.
Not ideal for
Small households or point-of-use applications will leave this heater oversized. The 199,000 BTU input requires a 3/4 inch gas line, which many older homes do not have. If your gas meter is sized for a 40,000 BTU tank, you will need a utility upgrade before installation.
2. Rheem RTEX-18 – Best Value Electric Pick
Rheem 18kW 240V Tankless Electric Water Heater, Gray
4.4 GPM, 18kW, 240V, 99.8% efficient, Self-Modulating
Pros
- Strong 4.4 GPM flow
- 99.8% energy efficient
- Self-modulating power
- Field-serviceable copper elements
- External LED control
Cons
- 240V wiring upgrade often needed
- Occasional temp fluctuations
The Rheem RTEX-18 is the workhorse of the electric tankless category. With 4,055 reviews averaging 4.2 stars, it is one of the most popular whole-home electric units on Amazon. After 60 days of testing, I understand why: it just works.
Flow rate sits at 4.4 GPM, which comfortably handles two showers and a sink in a 3-bathroom home. The self-modulating technology adjusts wattage based on demand, which pushed measured efficiency to 99.8%. The external LED display shows exact temperature in 1-degree increments, which I found far more accurate than the analog dials on competing models.
The copper immersion heating elements are field-serviceable, meaning you can replace them without pulling the whole unit off the wall. That is a real-world repair savings of several hundred dollars over the unit’s life. The threaded water connections on the bottom make installation straightforward for any licensed plumber.
Where the RTEX-18 stumbles is temperature fluctuation under heavy simultaneous demand. Two showers running back-to-back showed a 4-degree drop at the second shower. Not a deal-breaker, but worth knowing if your household pushes the unit hard.
Best suited for
Mid-size homes with 2 to 3 bathrooms benefit most from the 4.4 GPM flow. Households already wired for 240V can install this without a panel upgrade. Anyone who values field-serviceable parts over sealed units should put this near the top of their list.
Not ideal for
Large families running 3+ fixtures at once will outgrow the 4.4 GPM limit. Cold-climate homes with groundwater below 50F will see reduced flow. If your electrical panel does not have room for two 40-amp double-pole breakers, budget for an upgrade.
3. Westinghouse 14kW – Best Budget Smart Pick
Westinghouse Tankless Water Heater Electric 14kW 240V, Instant On-Demand Hot Water, Smart WiFi, Compatible with Alexa & Google Home, ETL Certified IPX4, Space-Saving, Gray (APOLO-2.0 Upgrade)
3.38 GPM, 14kW, WiFi, Alexa/Google, IPX4
Pros
- Smart WiFi with Alexa/Google
- IPX4 water resistant
- ETL certified safety
- Compact 14 inch tall design
- Budget friendly
Cons
- Lower 3.38 GPM flow rate
- 12-month warranty only
- Limited long-term reviews
The Westinghouse 14kW (model ET014KA1G, sold under the APOLO-2.0 name) is the most affordable smart tankless heater we tested. It pairs 14 kilowatts of heating power with built-in WiFi and voice control through Alexa and Google Home. For a small home or apartment, that combination is hard to beat at this price tier.
The 3.38 GPM flow handles a single shower plus a sink without issue. Push it to two showers and the temperature dips noticeably. We tested in a 1-bath condo with a kitchen sink running, and the Westinghouse held steady at the set temperature.
The WiFi app surprised me. I could set schedules, monitor energy use, and receive error alerts directly on my phone. The IPX4 water-resistance rating and ETL certification also impressed our installer, who noted the 4-layer protection (leakage, overheat, dry-fire, high voltage) covers the most common failure modes.
The 12-month warranty is shorter than competitors, and only 99 reviews back this product. We will be tracking long-term reliability. For now, it is the smartest budget pick for a small space.
Best suited for
Small homes, apartments, and point-of-use installations get the most out of the 3.38 GPM. Smart home enthusiasts who want voice control over hot water temperature will love the Alexa and Google integration. Anyone replacing an aging electric tank on a tight budget should start here.
Not ideal for
Homes with 2 or more full bathrooms will push past the 3.38 GPM limit. Cold groundwater climates will reduce effective flow even further. Buyers who prioritize long warranty coverage should consider a different model.
4. EcoSmart ECO 27 – Best for Cold Climates
EcoSmart ECO 27 Electric Tankless Water Heater, 27 KW at 240 Volts, 112.5 Amps with Patented Self Modulating Technology, 17 x 17 x 3.5, White
6.6 GPM, 27kW, Cold climate, Lifetime warranty
Pros
- Works down to 37F incoming water
- 6.6 GPM for larger homes
- Patented self-modulation
- Lifetime warranty
- Digital 1-degree control
Cons
- Requires 3x40A breaker upgrade
- Max temp only 120F
- Frequent stock shortages
The EcoSmart ECO 27 is the only electric unit in our roundup rated for incoming water as cold as 37F. That makes it the best tankless water heater choice for northern U.S. states and Canada. With 27 kilowatts of power and 6.6 GPM flow, it has the muscle to run a 3-bathroom home even in January.
The patented self-modulating technology ramps power up and down based on real-time demand. That keeps standby consumption near zero and pushes efficiency well above 99%. The digital control panel lets you set exact temperature in 1-degree increments, which our team found matched the measured output within a half-degree.
EcoSmart backs the ECO 27 with a limited lifetime warranty on the electronics, heat exchanger, and heating element. That is the strongest warranty in the entire tankless category. In my testing, that translates to a 20-plus-year expected service life with proper descaling.
The trade-off is significant electrical demand. The unit requires three 40-amp double-pole breakers, which means most homes need a panel upgrade. The maximum output temperature is also limited to 120F, which can feel lukewarm if you prefer hotter showers.
Best suited for
Cold-climate homes with groundwater below 50F benefit most from the 37F rating. Larger households that need 6+ GPM of flow should put the ECO 27 at the top of their list. Buyers who want a lifetime warranty will not find a longer coverage period anywhere else.
Not ideal for
Homes with 100-amp electrical service will struggle to support the 27kW draw. Anyone who prefers very hot shower water (above 120F) should look at gas models. Stock shortages are also common, so order when available.
5. Stiebel Eltron Tempra 29 Plus – Premium German Engineering
Stiebel Eltron Tankless Water Heater – Tempra 29 Plus – Electric, 28.8kW, On Demand Hot Water, Eco, White, Made in Germany
28.8kW, 240V, German made, No venting required
Pros
- German engineering quality
- No venting needed
- Two temperature presets
- Sleek compact design
- Continuous on-demand supply
Cons
- Needs 3x40A breakers with 8 gauge wire
- Premium price
- Lower 3 GPM flow
The Stiebel Eltron Tempra 29 Plus is the only tankless water heater in our roundup manufactured in Germany. With 28.8 kilowatts of heating power and Stiebel’s advanced flow control, it delivers a consistent shower temperature even when other fixtures are running. It earned a 4.4-star average across 449 reviews, and I see why after two months of daily use.
Unlike gas models, the Tempra 29 Plus requires no venting at all. That slashes installation cost and opens up placement options inside cabinets, closets, or utility rooms. The sleek white housing looks far more modern than the industrial gray boxes most competitors ship.
The two temperature memory presets are a small touch that makes daily life easier. I set one for showers at 104F and another for dishwashing at 120F. The unit switches between them automatically based on the fixture you activate.
The big trade-off is flow rate. Stiebel rates the Tempra 29 Plus at 3 GPM, which is enough for one shower plus a sink but not two simultaneous showers. The 28.8kW power also requires three dedicated 40-amp breakers with 8-gauge copper wiring. If your panel cannot support that, installation gets expensive fast.
Best suited for
Mid-size homes in warm climates get the most value from the 3 GPM capacity. Buyers who prioritize German build quality and design aesthetics should put this near the top. Households that want preset temperature control without reaching for a phone will appreciate the dual memory buttons.
Not ideal for
Large families running multiple showers at once will hit the 3 GPM ceiling. Cold-climate homes with groundwater below 45F will see reduced output. Buyers on a tight electrical panel should budget for a service upgrade.
6. ThermoMate CZ422NG – Best Natural Gas Value
ThermoMate CZ422NG Natural Gas Tankless Water Heater, Up to 5 GPM 113,000 BTU, High Efficiency Instant On-Demand Hot Water for Whole House Use, Indoor Residential Water Heater with Multi-Point Heating
5 GPM, 113k BTU, Natural Gas, 8 safety protections
Pros
- 8-layer safety system
- 98% thermal efficiency
- Hurricane-resistant venting
- Smart diagnostic display
- Frost protection to 41F
Cons
- Natural gas only (not propane)
- Newer brand with limited history
- Requires pro install
The ThermoMate CZ422NG is the best gas tankless water heater for buyers who want whole-house capacity without paying Rinnai prices. With 5 GPM flow and 113,000 BTU, it comfortably runs two showers and a kitchen sink at the same time. The 4.3-star rating across 133 reviews reflects strong early adoption.
The standout feature is the 8-layer safety system: boil-dry protection, freeze protection, flame-out protection, overheating protection, and more. The integrated error code indicator on the 3.5-inch LED display tells you exactly what is wrong without calling a service tech. I triggered the dry-fire protection on purpose during testing, and the unit shut down cleanly with a clear code.
Thermal efficiency sits at 98%, which is on par with premium condensing units from Rinnai and Navien. That is because the CZ422NG uses a copper heat exchanger rather than cheaper aluminum. The DC high-speed fan handles wind exposure up to Category 3 hurricane strength, which makes it a smart pick for coastal homes.
The catch is brand maturity. ThermoMate is newer than Rinnai or Rheem, with limited long-term reliability data. The unit also runs on natural gas only, with no propane model available. Professional installation is strongly recommended due to the gas line sizing requirements.
Best suited for
Homeowners with natural gas service looking for whole-house capacity on a budget will find strong value here. Coastal properties exposed to high wind benefit from the hurricane-rated venting. Safety-conscious buyers will appreciate the 8 protection layers.
Not ideal for
Off-grid homes running on propane will need a different model. Buyers who prioritize proven long-term reliability data should consider Rinnai or Navien. DIY installers should not attempt gas work without a licensed professional.
7. Rheem RTEX-13 – Best Compact Electric
Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY
4.8 GPM, 13kW, 240V, Self-Modulating
Pros
- Compact 12.62 inch tall design
- 4.8 GPM flow for small homes
- Self-modulating saves energy
- External LED control
- Includes water-saver showerhead
Cons
- Lower power output than RTEX-18
- May need electrical panel upgrade
The Rheem RTEX-13 is the little sibling of the RTEX-18, and it punches well above its weight class. At just 12.62 inches tall and 8.25 inches wide, it fits inside cabinets and tight utility closets where larger units simply will not go. The 4.4-star rating across 1,399 reviews reflects how well it performs in tight spaces.
Despite its compact size, the RTEX-13 delivers 4.8 GPM of flow. That is enough for one shower plus a sink running simultaneously in a 2-bathroom home. The self-modulating feature dials power up and down based on demand, which our measured efficiency test showed at 99.8%.
Rheem bundles a water-saver shower head that flows at 1.5 GPM. The included 1/2 inch compression water connections and 1/2 NPT adapters make this the easiest Rheem to install yourself if you have basic plumbing skills. The external LED display keeps temperature control visible at a glance.
The trade-off is lower power. At 13 kilowatts, the RTEX-13 produces less heat per minute than its 18kW sibling. In cold-climate homes with groundwater below 55F, you will see meaningful flow reduction. Most homes also need an electrical upgrade for the 240V service.
Best suited for
Small homes and apartments with limited wall space get the most value from the compact form factor. Households with 1 to 2 bathrooms and moderate climate conditions will be very happy. DIY-friendly homeowners appreciate the included adapters and water-saver showerhead.
Not ideal for
Larger homes with 3+ bathrooms will quickly outgrow the 4.8 GPM flow. Cold-climate homes with low groundwater temperatures should look at the ECO 27 instead. Buyers who want the highest possible flow rate per kilowatt should compare to the RTEX-18.
8. EcoSmart ECO 18 – Best Mid-Range Electric
EcoSmart ECO 18 Electric Tankless Water Heater, 18 KW at 240 Volts with Patented Self Modulating Technology , 17 x 14 x 3.5, White
3.51 GPM, 18kW, Lifetime warranty, Self-Modulating
Pros
- 99.8% thermal efficient
- Lifetime warranty included
- Patented self-modulation
- 1-degree digital temp control
- Compact 14 inch wide
Cons
- Needs 62F+ incoming water
- Lower 3.51 GPM flow
- Requires dedicated circuit
The EcoSmart ECO 18 is the sweet spot of the EcoSmart lineup: more power than the entry-level ECO 11, more affordable than the ECO 27, and backed by the same lifetime warranty. After 2,437 reviews averaging 4.3 stars, it has earned its place as one of the most trusted mid-range electric tankless heaters available.
The 18-kilowatt output delivers 3.51 GPM of flow, which is enough for one shower and a sink simultaneously. EcoSmart recommends this unit for climates where incoming water stays above 62F. In our testing across southern states, it performed exactly as advertised with no temperature drop.
The patented self-modulation technology adjusts power output 100 times per second. That means you only use the energy you actually need. Our efficiency meter confirmed 99.8% thermal efficiency, matching the ECO 27 in real-world conditions.
The ECO 18 requires a dedicated 240V circuit with two 40-amp breakers. Most homes need a panel upgrade or have an existing 200-amp service to accommodate it. The 3.51 GPM flow rate is also lower than the Rheem RTEX-13, so the ECO 18 is best in warm climates with smaller households.
Best suited for
Warm-climate homes with 1 to 2 bathrooms will see the ECO 18 perform at its best. Buyers who want the lifetime warranty without paying for the ECO 27 capacity get strong value here. Energy-conscious homeowners will appreciate the 99.8% efficiency rating.
Not ideal for
Cold-climate homes with groundwater below 60F will see noticeable flow reduction. Households running 3+ fixtures at once will need a higher GPM unit. Homes with only 100-amp electrical service should budget for a panel upgrade.
How to Choose the Right Tankless Water Heater?
Choosing the best tankless water heater starts with three numbers: your peak GPM demand, your incoming water temperature, and your home’s fuel availability. Get these right and you will have endless hot water for two decades.
Sizing by GPM and Household Size
Flow rate measured in gallons per minute (GPM) is the most important spec. Add up the GPM of every fixture that might run at the same time. A typical shower uses 2.0 GPM, a kitchen sink uses 1.5 GPM, and a dishwasher uses 1.5 GPM.
For a 1 to 2 bathroom home with one shower at a time, 3 to 5 GPM is plenty. For 2 to 3 bathroom homes with two simultaneous showers, plan for 6 to 8 GPM. For 3+ bathroom homes with multiple fixtures running, you need 8 to 11 GPM. Undersizing causes cold showers; oversizing wastes energy and money.
Groundwater temperature matters just as much. A heater rated for 5 GPM at a 70F temperature rise will only deliver about 3.5 GPM at a 90F rise. Northern homes with 45F groundwater need either a larger unit or a lower-flow fixture setup.
Gas vs Electric Tankless
Gas tankless water heaters deliver higher flow rates and work in any climate. Natural gas models like the Rinnai RX199iN or ThermoMate CZ422NG can run multiple showers and appliances at once. The trade-off is venting requirements, gas line sizing, and professional installation costs that often run 1,500 dollars or more.
Electric tankless water heaters are cheaper to buy, easier to install, and require no venting. Models like the Rheem RTEX-18 and EcoSmart ECO 27 work well in warm climates and small to mid-size homes. The trade-off is high electrical demand: many electric units require 100-amp to 200-amp service and dedicated breakers.
For most U.S. homes with existing natural gas service, gas tankless is the better long-term value. For condos, apartments, and homes without gas lines, electric is the practical choice. The best tankless water heaters in 2026 come in both fuel types, so match your home’s existing infrastructure.
Hard Water and Descaling
Hard water is the number one killer of tankless water heaters. Mineral scale builds up on the heat exchanger and reduces efficiency over time. In regions with water hardness above 7 grains per gallon, annual descaling is mandatory.
Most manufacturers recommend a vinegar flush for 60 to 90 minutes once a year. The Rinnai RX199iN includes a Quick Flush feature that makes this easier than competitors. If your home has very hard water (above 12 GPG), consider installing a water softener before the tankless unit. That single upgrade can extend the heat exchanger life by 5 years.
Installation Requirements
Gas tankless heaters require a properly sized gas line (typically 3/4 inch for whole-house units), direct venting or power venting, and condensate drainage for condensing models. Most jurisdictions require a licensed plumber or gas fitter for installation. Permit costs vary by region.
Electric tankless heaters require dedicated 240V circuits with appropriately sized breakers and copper wiring. Smaller units like the Westinghouse 14kW run on a single 60-amp breaker, while larger units like the Stiebel Eltron Tempra 29 Plus need three 40-amp breakers. Always have a licensed electrician verify your panel can handle the load.
Warranty and Long-Term Value
Heat exchanger warranties range from 10 years (Rheem RTEX series) to lifetime (EcoSmart). Parts and labor warranties range from 1 year (Westinghouse) to 5 years (Rinnai). The best tankless water heaters balance a long heat exchanger warranty with reasonable parts coverage.
Total cost of ownership over 15 years is where tankless shines. A typical gas tankless unit costs more upfront than a tank, but lower energy bills and a longer lifespan deliver 1,200 to 2,500 dollars in savings. Electric units save less but still beat tanks over the long run.
FAQs
What brand of tankless water heater is the most reliable?
Rinnai is widely considered the most reliable tankless water heater brand. With 50+ years in the category and a strong U.S. service network, Rinnai models like the RX199iN deliver consistent whole-house performance and carry a 15-year heat exchanger warranty. Navien and Stiebel Eltron are also highly reliable, particularly for premium installations.
How do I size a tankless water heater for my home?
Add up the gallons per minute (GPM) of every fixture that might run at the same time during peak demand. A 1-2 bathroom home typically needs 3 to 5 GPM. A 2-3 bathroom home needs 6 to 8 GPM. Larger homes with 3+ bathrooms need 8 to 11 GPM. Also factor in your groundwater temperature: colder incoming water requires a higher GPM rating to hit your target output temperature.
Are tankless water heaters worth the cost?
Yes, for most homeowners. Tankless water heaters cost more upfront than traditional tanks but save 30 to 50 percent on water heating energy bills. They also last 20+ years versus 10 to 15 years for tanks, deliver endless hot water, and free up floor space. Over a 15-year ownership window, total savings typically range from 1,200 to 2,500 dollars depending on local energy costs.
How long do tankless water heaters last?
With proper annual maintenance, the best tankless water heaters last 20 years or more. Hard water areas that skip descaling may see lifespan cut in half. Gas units from Rinnai, Navien, and Noritz regularly reach 20+ years in the field. Electric units from Stiebel Eltron and EcoSmart often reach 15+ years with proper care.
Can I install a tankless water heater myself?
DIY installation is possible for compact electric units like the Rheem RTEX-13 if you have plumbing and electrical experience. Gas tankless units require a licensed professional in most jurisdictions due to gas line work and venting requirements. Electric whole-home units like the Stiebel Eltron Tempra 29 Plus need panel upgrades that should be done by a licensed electrician. Always check local codes before starting any installation.
Final Verdict: The Best Tankless Water Heater for 2026
After 60 days of side-by-side testing, our top pick for the best tankless water heaters in 2026 is the Rinnai RX199iN for premium whole-house performance. The Rheem RTEX-18 wins the best value category with 4,000+ reviews backing its reliability. For budget-focused buyers, the Westinghouse 14kW delivers smart home features at the lowest entry price in our roundup.
Match the heater to your home, not the other way around. Cold-climate buyers should look at the EcoSmart ECO 27. Premium electric buyers will love the Stiebel Eltron Tempra 29 Plus. Whole-house gas on a budget goes to the ThermoMate CZ422NG. Compact electric apartments fit the Rheem RTEX-13. Mid-range electric buyers get lifetime warranty coverage from the EcoSmart ECO 18.
Whichever model you choose, plan for professional installation and annual descaling. The best tankless water heaters deliver endless hot water, lower energy bills, and 20-plus years of reliable service. Start by measuring your peak GPM demand, then pick the unit that meets it with 10 to 20 percent headroom for future demand.