Best Electric Tankless Water Heater 2020 Reviews & Buying Guides


Best Electric Tankless Water Heater

An electric tankless water heater (also called an on-demand water heater) is the best alternative to the standard tank heater that requires more space and energy.

This water heater is installed in a single appliance or under a sink. It heats water directly as it passes through the unit. How is it better than a tank water heater, and what are the factors to consider when purchasing a good one? Will this device meet your heating requirements and cut your heating costs?

This article answers the questions above and showcases the best-selling tankless water heaters you can find.

5 Recommended Electric Tankless Water Heaters

Product NameGPMWarranty
Stiebel Eltron Tempra1.5 – 4.57 years for leakage, 3 years for the parts
Sio Green2.5 – 4.02 years
EcoSmart ECO3.0Limited lifetime warranty
Rheem 2 RTEX-184.490 days
Bosch Electric Tankless1 – 1.55 years on the heating element, 1 year on other components

1. Stiebel Eltron Tempra Tankless Water Heater

Stiebel Eltron Tempra

Stiebel Eltron Tempra tankless water heater offers functionality that suits lots of household heating and wiring needs.

It’s available in various models with respective GPM and kilowatt requirements. For example, the Tempra 36 Trend requires a minimum flow of 0.77 gallons per minute (GPM) to activate the unit and produce hot water ranging from 86 to 140 ºF.

This Tempra 36 Trend model comes with a digital temperature display. Because of that, you get accurate temperature delivery and energy efficiency. You can control the temperature using just the buttons.

The thing provides non-stop hot water and energy savings with 0.99 energy factor (EF).

The heavy-duty copper heating chambers heat and maintain hot water efficiently, thanks to the heating mechanism (requires 12kW and 240V).

Additionally, the sleek, portable built is more than aesthetics but for easy maintenance, since it doesn’t require venting. Stiebel Eltron Tempra may be more pricey, but it comes with seven years of warranty for any leakage and three years for parts – securing your purchase.

  • German engineering makes it one of the most trusted brands in the water heating industry
  • Advanced Flow Control for continuous, unlimited hot water
  • 1.4 to 4.5 GPM depending on the water temperature
  • Silent operation when heating water
  • Tested and certified lead-free compliant
  • The most expensive unit in the list

2. Sio Green Heater

Sio Green SIO18 Electric Tankless Water

Sio Green’s infrared (IR) heating mechanisms, energized with quartz, don’t need water contact. The carbon-coated heating element, plus the quartz tubes, generate IR energy, which then heats the water.

Consequently, it amplifies the far-infrared (FIR) in the quartz tube (FIR is the region in the IR spectrum that’s closer to the microwave region than visible light) – that is the same technology NASA developed for various high-temperature purposes.

A good thing about the quartz elements is that they’re low-maintenance and don’t need venting – suitable for hard water since it prevents calcium deposits and rust, while also minimizing bacteria there. Aside from having superior heating efficiency and longevity, these elements are recyclable too.

The Sio Green has these maximum flow rates for their set temperature to heat water:

  • 4.0 GPM for 30º F
  • 3.6 GPM for 40º F
  • 3.0 GPM for 50º F
  • 2.5 GPM for 60º F

Electronic modulating technology predicts the required power by calculating the difference between the desired temperature and the current one. It can use 110 V or 220 V.

As an efficient tankless water heater, it has less than 20 inches of length that fits compact spaces in the kitchen, bathroom, RV, and sink. The innovative design is also suitable for both residential and commercial use, making this a high-demand heater.

  • Comes in five models with different voltages and features
  • Doesn’t need periodic flushing to maintain the desired level of efficiency
  • Far infrared ray and quartz heating mechanism
  • Can be installed in parallel, series, or hybrid mode
  • Smart modulating technology
  • Encompasses a wide temperature range
  • Heaviest unit in the list
  • Quite expensive

3. EcoSmart ECO 27 Electric Tankless Heater

EcoSmart ECO 27 Electric Tankless Water

If you want self-modulating control and technology that the first two products have, EcoSmart ECO is a cheaper alternative.

The ECO 27 electric tankless model operates at 112.5 amps and 27kW at 240 volts. It can heat up to 3.0 GPM at 37º F and has an activation flow of 0.3 GPM.

The copper and stainless steel parts are durable, efficient, and easy to replace. They are all housed in a small unit to save storage and mounting space in kitchens, sinks, and other household areas. Additionally, the stylish and innovative design easily matches house interiors.

Moreover, the digital temperature control has increments of one degree. It allows you to control the temperature of incoming water. The ECO 27 utilizes only the amount of required energy based on the preset water temperature.

EcoSmart ECO is one of the few units on the market that come with a lifetime warranty. For its mid-range price and energy savings in the long-run, this unit is cost-effective and a must-have.

  • Advanced self-modulating technology that cuts power consumption
  • Saves 50% in the energy bills, making it eco friendly
  • Compact design
  • Can handle two sinks simultaneously
  • Still expensive compared to other units in the heating industry

4. Rheem 2 RTEX-18

Rheem 240V 2 Heating Chambers RTEX-18

Rheem may not be an expensive, top-quality brand, but it delivers reasonable functionality and features. One of Rheem’s top-selling electric water heating machine is the Rheem 2 RTEX-18. At a lower cost, it offers unlimited hot water to residential and commercial establishments.

Like the other units mentioned above, the Rheem 2 RTEX-18 has an external digital thermostatic regulator with an LED display for accurate temperature control.

The heavy-duty copper has two heating elements that deliver a flow rate of up to 4.4 GPM. The installation is straightforward, and the bottom has 3/4-inch NPT water connections and threaded construction for easy replacement.

The challenge, however, is its medium sized dimensions which might take up too much space in the shower or under the sinks. For some homeowners, this minor drawback is probably not the factor they are concerned with especially if they have much space in these particular areas.

  • Relatively affordable compared to the other units here
  • Saves energy through the self-modulation function
  • Easy to install because of the threaded design and water connections
  • Possible temperature fluctuation

5. Bosch Electric Tankless Water Heater

Bosch Electric Tankless Water Heater

The Bosch Electric Tankless is probably one of the cheapest electric tankless water heaters. So, if you have limited cash, this is the perfect choice for you.

The dimensions are compact, so it is easy to install. It can conveniently and seamlessly mount under the sinks and cabinets. One thing that people like about it is that it can also be an outdoor tankless water heater.

Notwithstanding the smart design that blends in well with the home interior, you can install it on patios, garage, wet bars, and boats. The installation is easy, and it can be mounted horizontally or vertically.

It operates at 220 volts and has an energy efficiency of up 98% with minimal standby loss. The flow rate is up to 1.5 GPM, and the water pressure range is 10 to 150 PSI. If this is good enough for your demand for hot water, then the Bosch Electric Tankless is the perfect, inexpensive product for you.

  • The most affordable unit
  • Compact, lightweight, and attractive design
  • Easy to install in small spaces because it’s properly sized
  • Can be mounted in outdoor areas such as kitchen patios and boats
  • Runs at 98% thermal efficiency causing this to peak demand
  • Weak hot water flow at 1.5 GPM
  • No thermostatic control and digital display
  • Doesn’t have a smart modulating feature

Tankless Water Heater Buying Guide

First, we discuss the difference between a traditional tank water heater and a tankless unit. Then, we provide a detailed buying guide that would help you greatly when it’s time for shopping.

Tank vs. Tankless Heater?


To answer this question, we’ll describe how each type of water heater works.

Storage tank heater

The traditional water heating device is the storage-tank water heater. The majority of households use it.

This heater is an insulated tank that holds around 30 to 50 gallons of water. The heating mechanisms increase the water temperature and store it until it is needed.

A pipe is attached to the top, from which the hot water can travel to the bathroom, kitchen, and sink. The heating power of storage tank water heaters usually comes from electricity or natural gas (NG).

Natural gas powered, storage tank water heaters are typically expensive, but they utilize 50% less energy than the electric ones. They also have integrated valves for water flow and temperature control. These valves open when either the pressure or temperature rises beyond the preset levels.

Tankless heater

On the other hand, tankless water heaters are 24 to 34% more energy efficient than the storage tank water heaters for every 41 gallons (or less) hot water consumption per day. Homeowners that use around 86 gallons may enjoy energy savings of an additional 8 to 14%.

One major drawback of the tankless water heater is it’s more expensive than the traditional storage water heater. However, it operates with less energy, so you save money in the long run.

As the name implies, this type of water heater does not store water in a tank. Instead, it utilizes high-powered burners, usually gas or electricity-powered, which promptly heat the water supply as it passes through a heat exchanger. Then, the hot water instantly goes to household water channels (such as faucets and shower heads).

Electric tankless water heaters are better for your hot water demand since they last quite a long time. Electric tankless heaters last for 7 to 10 years, and gas tankless water heaters operate up to 20 years. On the other hand, the traditional storage tank heater on the market can last up to 15 years.

Furthermore, as you’ve seen in the photo above, tankless units don’t consume too much storage space – these things are ultra-compact. Plus, you won’t have to wait for 15 to 20 minutes to warm your water. These devices deliver two to four gallons of hot water per minute. They generate hot water only when needed, which is a good thing if you’re very eco-friendly.

Going Tankless? Keep These in Mind


If you are thinking about going tankless, then you should know how to choose a suitable one for your household. Not all of the marketed best-selling units live up to the hype. So, before you go to the store and purchase one, read our buyer’s guide. Make sure you have in mind these essential factors.

Incoming water temperature

You can preset the incoming water temperature through digital thermostatic control. Many tankless water heaters are integrated with this knob to set the desired water output temperature. A digital LED display is also available in many units.

It’s also worth noting that the temperature affects the water flow. For example, the 30º F incoming water may have a water flow of up to 4.0 GPM, while 60 ºF water may flow at 2.5 GPM. Higher temperature of the incoming water means a lower flow rate.

The initial cost for installation

These electrically powered tankless water heaters cost from $90 to $900, not including the installation costs. The first-time installation should be done by a professional, as it involves securing the vent, water, and electricity connection, making them leak-free. Other than that, they also upgrade the wiring and circuit-breaker panels.

If your home is already tankless water heater-ready, you can install it by yourself. Most tankless water heaters come with installation manuals and technical specifications that let you decide if it’s appropriate for your household.


Electric, tankless water heaters have more parts than the traditional storage water tanks, meaning they tend to have more repairs. Although many of the products come with a warranty, not all are comprehensive, and manufacturers are not immediately available to repair.

Durability is an important consideration. Some units have heating elements that don’t need periodic replacements and direct contact with water. Units made of quartz are ideal because they are long-lasting, rust-resistant, and suitable for hard water.



You may sign up for a professional to provide yearly annual maintenance service. The maintenance includes cleaning, changing the water and air filters, and examining the electrical wirings and water flow.

In places with hard water, a vinegar flush is required every 500 hours to remove mineral buildup and prevent clogging of the unit. This task takes about 20 minutes and can be performed by the homeowner or a professional. You don’t need to do this if your water heater unit has quartz elements.

Final Verdict

We have presented hopefully good tankless water heater reviews. All five products have efficient heating mechanisms that save energy and power. After thorough consideration, the EcoSmart ECO stands out among the list – it comes at a reasonable price while being loaded with practical functionalities and features. It’s a great choice overall for the long term.

The 4.0 GPM at 64-96º F and 3.0 GPM at 49 ºF options are the most reasonable and relatively sufficient. Although the EcoSmart ECO is long-lasting, with durable construction, you have peace of mind for its lifetime warranty that most electric water heaters do not have. author Anastasia Russell
Anastasia is a 26-year-old blogger who always motivated to observe the ways humans interact with technology. She is currently undertaking a master degree program at the Uppsala University specializing in Human-Computer Interaction & Design Program.
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