page title icon 10 BEST TANKLESS WATER HEATER 2021 | Reviews and buying guide

Need hot water, and still can’t figure out which one is the best tankless water heater? Don’t worry we have got you covered in this extensive review of the best tankless water heaters available in the market. Here we shall provide you an in-depth detail of some of the top tankless water heaters with their pros and cons, so you can select the one that best fits your requirements.

But before digging into the details of the best tankless water heaters one must have sufficient knowledge that what a tankless water heater is. How is it better than tank water heaters and does it work?

You need not worry about any of these questions because we have got you covered. A tankless water heater also known as instantaneous or instant water heater unlike  conventional tank water heaters does not have a water storage tank. Rather it heats cold water as it passes through the pipe. So you need not to wait for the water stored in the tank of the heater to warm up. Such type of water heaters uses sensors, when a hot water tap is opened the sensor turns on the burner or electric component that heats the water.

Tankless water heaters are more efficient than tank water heaters as the fuel is only used when hot water is required. Unlike that conventional water heaters have a constant consumption of fuel. Tankless water heaters consume less fuel saves more time and have a longer lifetime. Given below are the details of some best tankless water heaters. We have sorted out the best heaters for you after extensive research. These are placed in a position according to the best reviews and their features. You must go through these details to choose the best one for yourself.

Best Tankless Water Heater 2021

We have selected the 10 best tankless water heaters for our various tests and comparisons that are available in the market.

Image Product Details   Price
backpac Rinnai RU180iN Brand: Rinnai
Model: RU180iN
Weight: 64 Pounds
Voltage: 120V
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backpac EcoSmart ECO 27 Brand: EcoSmart
Model: ECO 27
Weight: 13.75 Pounds
Amperage: 112.5
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backpac Stiebel Eltron 224199 Brand: Stiebel Eltron
Model: Tempra 24
Weight: 16.1 Pounds
Voltage: 208 volts
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backpac Rinnai V75iN Brand: Rinnai
Model: V75iN
Weight: 45.6 Pounds
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backpac Stiebel Eltron Brand: Stiebel
Model: Tempra 24 Plus
Weight: 1 Pound
Voltage: 208 Volts
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backpac Rinnai RL75IN Brand: Rinnai
Model: RL75iN
Weight: 50 Pounds
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backpac Rheem RTEX-18 Brand: Rheem
Model: RTEX-18
Weight: 14.8 Pounds
Voltage: 240 Volts
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backpac Rheem 240V Brand: Rheem
Model: RTEX-13
Weight: 14 Pounds
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backpac Bosch Electric Mini-Tank Brand: Bosch
Model: Tronic 3000 T
Weight: 17.3 Pounds
Voltage: 120V
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backpac Eemax EEM24027 Brand: Eemax
Model: EEM24027
Weight: 13.75 Pounds
Voltage: 240V
Check Price

1. Rinnai RU180iN Sensei Super High-Efficiency Tankless Water Heater

Rinnai RU180iN Sensei Super High-Efficiency
  • High Efficiency
  • Highest GPM Flow Rate
  • Wi-Fi Connectivity and Mobile App Controlled
  • Energy Star Certification
  • Little bit costly


Rinnai, a brand that has been manufacturing water heaters since 1925, knows how to keep the standards high. With each passing year that brand shows up with advancement in technology. Rinnai RU180iN is the best example of innovative technology. It has surpassed all other tankless water heaters in terms of features hence gained the first spot in our list of best tankless water heaters.

The water heater has a huge flow rate of 10 GPM. None of the other best tankless heaters can exceed this flow rate. However, the flow rate varies with the groundwater temperature. With such a high flow rate this water heater can be used in bigger to normal-sized houses where the supply requirement varies. To provide the consumer with a constant supply of hot water the unit has been embedded with Circ-Logic Technology. The technology recirculates hot water in the pipes so you get pepping out water the moment you turn on the tap.

With all these advanced features Rinnai RU180iN is efficient. The unit is available for both fuel types e.g natural gas and propane. And the installation of the unit is a quick and easy process. The size of the best natural gas tankless water heater is such that it best suits for indoor installation. As it does not take much space so can be placed anywhere inside the house. Moreover, to meet modern-day requirement this tankless water heater can be connected through Wi-Fi thus it can be controlled through a mobile application. You can monitor your unit from anywhere. Also comes with an energy star certification.

Key Features

  • Natural gas Water Heater
  • Stainless Steel Body
  • Circ-Logic Technology
  • Compact Size and Easy Installation
  • 10 GPM Flow Rate
  • Can be connected through Wi-Fi
  • Indoor Installation

2. EcoSmart ECO 27 Electric Tankless Water Heater

EcoSmart ECO 27 Electric
  • Easy Installation
  • Highest Efficiency
  • Lifetime Warranty
  • Low cost
  • Flow Rate decreases at low temperature


Renowned products mostly come from renowned brands. The same is the case in tankless waters heaters. EcoSmart provides you with some of the best electronic products in the market, and it has come up with a tankless water heater that meets all the criteria of the best water heater. The only restriction of an instant water heater is that it provides less GPM (Gallon Per Minute) of hot water. But EcoSmart ECO 27 Electric Tankless Water Heater offers you an exceptional flow rate of 6.6 GPM.

Due to its extraordinary flow rate, this water heater can be used as a single unit for the whole house. It must be expected that this much high flow rate would increase the size of the unit. But that’s not the case. The compact design of the electric water heater has made it more demanding. EcoSmart ECO 27 has components made of copper and stainless steel that increases its efficiency. The system has an efficiency of 99.8%. The latest self-modulating sensors, sense the amount of energy required. The system has a unique digital display that makes its use easier than ever. This water heater can handle water with a temperature as low as 43 degrees Fahrenheit. 

All these features are available at a very budget-friendly price that makes EcoSmart SCO 27 the most demanded and among best rated tankless water heater under 500 $.

Key Features

  • Compact Size 17″ x 17″ x3.75″
  • Copper and Stainless steel construction
  • 99.8% Efficiency
  • Digital Control Display
  • 6.6 GPM Flow Rate
  • Self-Modulating Sensors
  • Handle Water with temperature as low as 43 F

3. Stiebel Eltron 224199 240V, 1 Phase, 50/60 Hz, 24 kW Tempra 24 Plus Whole House Tankless Electric Water Heater

Stiebel Eltron 224199 240V, 1 Phase, 50/60 Hz
  • High Efficiency
  • No Annoying Sounds
  • Budget-Friendly Price
  • Less Temperature Fluctuations
  • No Venting Required
  • Needs to be installed by a licensed professional to keep the warranty valid


Tired of the noises water heaters make and fed up with this constant frustration? Then Stiebel Eltron Tempra is the best option for you. The unit has a digital control display. The feature that makes it one of the best tankless water heaters is that it has no mechanical valves that usually make annoying sounds. The unit has a sleek and eye-catching design. The unit has a digital control display

It has a flow rate of up to 5 GPM, however the flow rate also depends on the temperature of the water. Self-modulating technology controls the amount of energy used. The feature that distinguishes this product from other best tankless water heaters is that it provides a constant supply of hot water without any fluctuation. The Dynamic Advanced Flow Control used in this tankless water heater automatically increases the hot water supply when the water demand is increased.

Stiebel Eltron has an automatic thermostat that controls the water temperature. The power modulation system provides maximum efficiency of 90%. Isn’t that amazing?   So if you are a person who is very concerned about the power consumption of the appliance that you use, then Stiebel Eltron Tempra is the best option for you. The incredibly constant flow rate makes this tankless water heater perfect to use in northern as well as southern areas. Below given key features will further help you in making the selection much easier.

Key Features

  • Digital Temperature Display
  • Controlled Temperature Regulation
  • Advanced Flow Control Technology
  • Efficiency of 90%
  • 5 GPM Flow Rate

4. Rinnai V75iN Tankless Hot Water Heater

Rinnai V75iN Tankless Hot Water Heater
  • High Flow Rate
  • 60 Months Parts Warranty
  • Time Saving with ThermaCirc360 Technology
  • Mobile Control Feature
  • Quite Heavy
  • Requires Special Vent Piping


Rinnai has utilized its 100 years’ experience in water heaters manufacturing and has developed a tankless water heater that fulfills all the requirements of any modern day user. Keeping a close look at the needs of the customer they have designed a gas tankless water heater that is compact in size but wide in its features.

Rinnai V75iN is a tankless water heater that can compete with any best-selling tankless water heater due to its diverse features. With an amazing flow rate of 7.5 GPM, this model defeats all other tankless heaters far behind. With such a flow rate you will never run out of hot water while doing laundry or using a dishwasher. The unit is equipped with ThermaCirc360 technology that keeps the hot water circulating in the pipes thus saving a lot of water and time. With this innovation, the water that is typically wasted while waiting for hot water is saved.

An additional feature that helps Rinnai V75iN gets its position in top tankless water heaters is that it can be controlled with a mobile app. With R-2.0 mobile app you can control your water heater. The feature makes it perfect for any modern-day user.  Despite all these exceptional features the tankless water heater has a small size. The unit occupies such a small space that it fits perfectly indoors as well. The best gas tankless water heaters save every inch of space. The small size means less CO2 emission. Thus increasing the efficiency of the water heater.

Key Features

  • 7.5GPM Flow Rate
  • ThermaCirc360 Technology
  • Compact size 14.04 x 9.27 x 26.90 inches
  • Less CO2 emission
  • R-2.0 Mobile App Control
  • Wi-Fi Connectivity
  • Tankless Gas Water Heater
  • Propane and Natural Gas
  • High Efficiency

5. Stiebel Eltron Tankless Water Heater – Tempra 24 Plus – Electric

Stiebel Eltron Tankless Water Heater
  • Energy Saving Monitor
  • 90% Efficiency
  • Electronic Flow Sensors
  • Quite Affordable
  • Light in Weight

  • Low Flow Rate for Higher Demand


In a market with such great competition, every brand tries to set up a mark no one can achieve. For the purpose, they come up with products that have such exceptional features that are not available in any product of the competitor’s brands. Stiebel Eltron Tempra 24 has many features that many other tankless heaters lack.

This tankless water heater is patented with advanced German technology that provides a constant supply of hot water without any fluctuation. With the Advanced Flow Control, you will never run out of hot water and you will be able to enjoy your shower without any interruption. Just like the prior model of Stiebel Eltron Tempra, this water heater produces no noise, offering you a fuss-free experience. The model has a very compact size that can easily be mounted on a wall or placed down the sink.

European engineered design with Electronic flow sensors turns on the strong copper coils that heat the water instantly. Stiebel Eltron Tempra 24 has a Flow rate of 4 GPM that is quite sufficient for a small home. Not only the unit has a sleek and eye-catching look, but also a unique digital display that helps the user to operate it more quickly and efficiently. The electric tankless water heater has an extraordinary efficiency of 90%.  The feature that attracts most of the customers towards itself is that it has an energy-saving monitor. The monitor enables the customers to keep a track of how much energy they have saved.

Key Features

  • 4 GPM Flow Rate
  • Advanced German Flow Control System
  • 90% Efficiency
  • Digital Temperature Control Display
  • Electronic Flow Sensors
  • Compact and Sleek Design
  • Copper Interior

6. Rinnai RL75IN Tankless Water Heater, Large, RL75iN-Natural Gas/7.5 GPM

 Rinnai RL75IN Tankless Water Heater
  • High Flow Rate
  • Circ-Logic Technology for Recirculation of water
  • 60 Months Parts Warranty
  • Wi-Fi Connectivity
  • Quite Heavy


Rinnai is a renowned brand that manufactures quality water heaters. With an extensive experience of more than 100 years in the field of water heaters production, the brand keeps on introducing its new models. These new models of tankless water heaters have all the features of the prior models along with many additional features. Rinnai RL series is an extension to its V series that not only inhibits the features of the V series but has much to offer.

Rinnai RL75iN has all the features that are customary to all Rinnai series like High Efficiency, Fluctuation Free supply of hot water, Exceptional Flow Rate, and many more. But that’s not it! The new series has many updated and additional features. The tankless gas water heater has been equipped with Circ-Logic Technology. The technology embedded in this series of water heaters allows the circulation of hot water in pipes. You will get a supply of hot water the moment you turn off the tap. This advancement saves a lot of time and water that typically goes wasted.

The unit also includes isolation valves reducing the noise that’s been produced due to mechanical valves. Just like the V series Rinnai RL series also offers Wi-Fi connectivity. It has an amazingly high flow rate of 7.5 GPM, enough to supply hot water to a big house. It is available for both natural gas as well as propane that just diversify its use. Whenever top tankless gas heaters are listed Rinnai water heaters always stand on top due to all these extraordinary features.

  • 7.5 GPM Flow Rate
  • Circ-Tech Technology
  • Includes Isolation Valves
  • High EfficiencyCompact size 14 x 9.3 x 23 inches
  • Natural Gas Tankless Water Heater
  • Wi-Fi Connectivity

7. Rheem RTEX-18 18kW 240V Electric Tankless Water Heater

Rheem RTEX-18 18kW 240V Electric
  • Quiet and Efficient
  • Very Budget Friendly
  • Easy Installation
  • Advanced Self Modulation
  • Sometimes shows an E5 Error


Just with the advancement in technology, water heater manufacturers are producing such products that meet all the requirements of every type of user. Rheem RTEX-18 is such a product that can leave many other tankless water heaters far behind due to the limitless features. The best tankless water heater offers all exceptional features without putting any strain on its beautiful look.

The key features of the unit include a Flow rate up to 4.4 GPM that is sufficient to fulfill the hot water requirement of an average home. The water has an eye-catching sleek design with a digital LED display and a thermostat. Rheem RTEX-18 is compact and the installation is super easy, that you can do it yourself without the assistance of any professional. Its easy installation saves a lot of user’s money that he would spend on any electrician.

Another amazing feature that makes RTEX-18 one of the best tankless water heaters is that it produces no sound. The unit provides maximum output without any irritating sounds. This feature enables its users to place the unit anywhere in the house as it would not bother them at all. Equipped with the most advanced Self-Modulation Technology the water heater adjusts power itself to meet hot water demand. The unit has 2 strong copper heating components that ensure maximum performance and durability. All these features are available at a very low cost that makes the unit the best tankless water heater under 500$.

Key Features

  • Flow Rate of 4.4 GPM
  • Advanced Self Modulation Technology
  • 2 Copper made Heating Components
  • Brass Top for Durability
  • Digital Thermostat with LED Display
  • Sleek Design and Compact Size

8. Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater

 Rheem 240V Heating Chamber RTEX-13 Residential
  • Small Size
  • Very Low in Cost
  • Highest Efficiency
  • Simple and Easy Installation
  • Low Flow Rate Not sufficient for demands more than 3.17 GPM


If you live alone, with your partner, or in a place where your hot water usage is not much then Rheem RTEX-13 is the best option for you. Where some people want to have a water heater that has maximum GPM capacity, some individuals want to purchase a tankless water heater that just meets their exact requirements. That’s a smart move, because by doing so one not only saves the purchase money of the heating system but you save the monthly energy consumption cost. The smaller the unit, the lesser the energy consumed, hence lower the cost.

Rheem RTEX-13 is the best tankless water heater for small homes with fewer individuals. The unit has a Flow Rate up to 4 GPM. It has an external digital thermostat with an LED Temperature display. The unit is small in size and does not occupy much space. It provides a maximum efficiency of 99.8%. Rheem RTEX-13 has the highest efficiency than any other best tankless water heaters.

Just like RTEX-18 this water heater also features 2 copper made heating elements that warm up the water instantly and without any fluctuation. Rheem has made sure to serve their customer to the best of their potential, thus offers simple installation of the unit. So you get more features in less price. The price of Rheem RTEX-13 is as low as 252$. This budget-friendly gadget offers so much is such a cheap price that no one resist considering this water heater before buying one.

Key Features

  • External Digital Thermostat
  • Flow Rate up to 4 GPM
  • Indoor Installation
  • LED Temperature Display
  • 2 Strong Heating Components
  • Self-Modulating Power Contro
  • High Efficiency of 99.8%

9. Bosch Electric Mini-Tank Water Heater Tronic 3000 T 4-Gallon (ES4)

Bosch Electric Mini-Tank Water Heater
  • Very Compact Size
  • Personal Installation
  • Very low in cost
  • High purchase volume
  • Mini-tank for water storage


As the name suggests Bosch Electric Mini-Tank Water Heater is not a tankless water heater but it works just like a tankless water heater. The instant water heater is smaller in size than many tankless heater and heats the water more instantly than any of them. So it has all the features to compete with the best tankless water heaters. It’s best to use as a specific purpose water heater like with your sink. It can be accommodated at a very small place for instance under the sink and provides instant hot water at the place of use.

The Bosch Electric Mini-Tank water heater has an extremely easy installation process. All you need to do is to plug its cord into the switch and it’s ready to easy. No need for professional and complete installation. It has an efficiency of 98%, competent to any best tankless water heaters. It has a thin glass lining to the tank, that improves its performance and provides its users with such a great thermal efficiency. And it can hold up to 4 Gallons of water.

The unit also includes a relief valve that makes handling the unit much easier. The feature that demands to place this product in the list of top tankless water heaters is its exceptionally small size and the premium quality material that is used while manufacturing it. The thin glass lining gives a guarantee to the long life of the water heater. The unit can be placed down a sink, placed on a cabinet, or simply mounted on the wall. So if you are on a hunt for the best electric water heater for a sink or any specific area of your home Bosch Electric Mini-Tank Water Heater is the best option for you. Its extensive features and extremely low price also makes it one of the most reviewed water heater.

Key Features

  • Holds up to 4 Gallons of Water
  • Small in size 13.75 W x 13.75 H x 13.5 D Inches
  • Premium Glass Lined Tank
  • Lightweight and Portable
  • 98% Efficiency
  • Super Easy Installation
  • Indoor Water Heater
  • Includes Relief Valves

10. Eemax EEM24027 Electric Tankless Water Heater, Blue

Eemax EEM24027 Electric Tankless Water Heater
  • Advanced Self Modulating Technology
  • Instant and Constant Hot Water Supply
  • Quite Affordable
  • Requires 3 sets of 220V


If you are tired of the water heaters that do not provide a constant supply of hot water and have constant fluctuations, then Eemax EEM2407 Electric tankless water heater is a very good option for you. This tankless water heater offers a constant supply of hot water without any interruption. The unit has been embedded with one of the most advanced self-modulating technology that monitors the power consumption of the water heater. With this technology, the system automatically increases power when the requirement for the water increase.

Compact size that is a must quality of any best tankless water heater, is also the distinctive feature of the EEM207 tankless water heater. Despite its small size, the tankless water heater is enough to supply hot water to multiple appliances at the same time. The feature makes it a perfect fit for a bigger house with higher demands of hot water. It can easily be mounted on the wall with very little effort. For customers that demand products exactly to their requirements for them, it is the best water heater as it is available in different sizes. All provides you with different Flow Rates.

The unit saves a lot of its users time as it provides hot water instantly. Now you don’t need to go for a shower and wait until the cold water runs out the pipe and you finally get a hot water bath. And above all this tankless water heater is available at a really good price that everyone can afford and any brand will charge for such a water heater.

Key Features

  • Self Modulating Technology
  • Electric Tankless Water Heater
  • Lightweight and small in size
  • Easy Installation
  • External Thermostat
  • Digital Temperature Display
  • Stainless Steel Body
  • Instant and Continuous water supply

Rinnai RL75IN Tankless Water Heater

Ultimate Buyer’s Guide to Buy Best Tankless Water Heater

After reading the details of some of the best tankless water heaters you might have chosen the one that best fits your requirements. But before buying one you must consider some factors that you must consider to avoid any regret in the future.


The first thing that you must take into consideration is your budget. Once you have a clear idea of your budget you can easily shortlist the products that fall in your budget range. A good tankless water heater is the one that offers the best value for your money. Higher prices better the features. You must choose wisely.

Flow Rate (GPM)

It’s always wise to keep your requirements list clear, in this way you will be able to select the best product. Every tankless water heater has been rated for a specific flow rate. The flow rate is measured in gallons per minute (GPM). Higher the flow rate more amount of hot water the water heater can provide at a time. Bigger houses need water heaters with greater GPM. Make the right choice as a wrong decision can waste all of your money.

Power Input (BTU)

Power input is the amount of energy that is required to warm up the water. Selecting the right tankless water heater is important is it is going to affect your energy consumption thus your energy cost a lot.


You must consider which fuel type you can afford or that is available at your house. There are two main types of tankless water heaters. One that is electrically operated and the other that operates on either gas or propane. Electric heaters are more efficient and are less in weight.


An important factor that most people neglect while selecting a tankless water heater is the size of it. But it is as important as the price of the water heater. Because water heater is of no use if it does not accommodate in available space.


Are Tankless Water Heaters Better Than Typical Water Heaters?

Surely, Tankless water heaters are better than typical water heaters as they provide an instant supply of hot water, occupy less space, and are much more energy-efficient.

How do we know which tankless water heater is the best?

The best tankless water heater is the one that perfectly fits your requirements. Moreover, you can easily tell which one is better by comparing the specifications of all the best tankless water heaters.

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