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7 Best Tankless Water Heaters of 2021 – Reviews & Buyer Guide

Tankless water heaters can deliver unlimited hot water on-demand, and they are also highly efficient, potentially saving you money. If you are looking for the best tankless water heater for your home, here are our top picks to help you select the right one for you.

Ecosmart ECO Electric Tankless Water Heater
Ecosmart ECO Electric Tankless Water Heater

  • Highly advanced self-modulating technology – save up to 60% on bills
  • Lifetime residential warranty – for complete peace of mind
  • Easy to use – intuitive control panel
  • Extreme efficiency – rated as being 99.8% energy efficient
  • Temperature range 80°-140°F – can also be set in centigrade

ECOTOUCH Tankless Water Heater
ECOTOUCH Tankless Water Heater

  • Inexpensive option – an affordable tankless water heater
  • Ideal for single uses – for example, to heat the water to a single sink
  • Compact and unobtrusive – easy to install anywhere
  • Easy to use – simple and intuitive controls
  • Highly efficient – 98% energy efficiency to help reduce bills


The Best Tankless Water Heater on the Market 2021

1. Stiebel Eltron 24 Plus Tempra Tankless Water Heater

Stiebel Eltron Tankless Water Heater

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This is an electric tankless water heater from well-regarded German brand Stiebel Eltron. It belongs to the company’s Tempra Plus range and boasts several advanced features.

It is able to deliver a continuous flow of uninterrupted hot water thanks to Stiebel Eltron’s patented Advanced Flow Control system. This allows it to maintain the water temperature by reducing the flow slightly if the hot water required exceeds the amount available.

This model is an ecological option that will help reduce your electricity bills. It achieves this by automatically modulating the flow of water, delivering only the amount of hot water that is necessary and no more.

One feature we particularly like is that it includes a display panel that tells you how much energy has been conserved by the system, allowing you to track exactly how much money the unit is saving you.

It is capable of delivering hot water from 86°-140°F, and it also includes temperature setting buttons that remember your preferences, making it quicker and easier to program.

Another positive is that it runs very quietly – if you don’t want a water heater that makes lots of noise every time you use it, this could be a good option.

If we have to pick some downsides, one would be that this is not a budget-friendly option. However, while there are less expensive heaters available, this is a high-quality unit, and you have to expect to pay more for top-end equipment.

Also, while this model does well in smaller homes, if you need to run multiple fixtures at the same time, you might find this unit struggles a little. Although a couple of showers running at the same time won’t be a problem, if you push it too hard, it won’t be able to keep up.

All in all, this is a highly efficient and reliable water heater that does the job it was designed for very well. If you aren’t put off by the high price tag, this is a model that is well worth considering.


  • Advanced Flow Control – automatically adjusts to maintain water temperature
  • Small footprint – compact unit won’t take up much space
  • Eco-friendly – saves electricity when less is required
  • Tells you how much energy you save – provides feedback on usage
  • Noiseless operation – as quiet as you could hope


  • Relatively high price – not a budget option
  • Can struggle if multiple users need water – better for smaller homes

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2. Ecosmart ECO Electric Tankless Water Heater  Our Top Pick 

Ecosmart ECO Electric Tankless Water Heater

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As you can probably guess from the name, EcoSmart is a company that specializes in making efficient water heaters that are designed to be kind to the environment.

The company that produces this unit has developed some of the most advanced water heater self-modulating technology that currently exists, which means one of these can save you up to 60% on your electricity bills.

This is partly due to the extremely high efficiency rating – this water heater runs at 99.8% energy efficiency, meaning that practically all the energy it consumes is used for heating water and almost none is wasted.

We like the way it looks, too. It has a sleek, modern design with a small footprint, and it’s easy to control using the intuitive digital control panel. It has a temperature range of 80°-140°F – and you can also change this to centigrade if you prefer just by holding the button down.

One other big plus is the fact that it comes with a lifetime limited warranty for residential users. However, unfortunately, the warranty is void if you install it yourself, meaning you have to pay a professional to do it.

The only other downside is that it may struggle with multiple fixtures or in areas with cold groundwater. Larger versions exist that can deal with these issues, but even then, there are limits to their capabilities.

However, for anyone in a smaller home who doesn’t need to use too many fixtures at once, this could be a great option. It’s reasonably priced and will save you money in the long run. If those sound like qualities that interest you, it should be worth checking out.


  • Highly advanced self-modulating technology – save up to 60% on bills
  • Lifetime residential warranty – for complete peace of mind
  • Easy to use – intuitive control panel
  • Extreme efficiency – rated as being 99.8% energy efficient
  • Temperature range 80°-140°F – can also be set in centigrade


  • May struggle with multiple fixtures – although bigger versions exist
  • Warranty void if self-installed – need to pay for a professional

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3. Stiebel Eltron 223422 Electric Whole House Tankless Water Heater

Stiebel Eltron Tankless Water Heater

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This is another tankless water heater from Stiebel Eltron, this time from the company’s Tempra range rather than the Tempra Plus line. This means it is not quite as advanced as the model we just looked at, but it is still a high-quality, high-performance unit.

Tempra water heaters provide a consistent flow of hot water, even when flow rates vary. Thanks to its onboard auto-modulation technology, it adapts automatically to demands.

When more hot water is required for more fixtures, it uses the necessary power, but when demand decreases, it reduces power consumption, helping save money on electricity bills while also helping to protect the environment.

It is also a highly efficient unit. At around 99% efficiency, installing one of these will mean that almost no power is wasted – again, helping to reduce your monthly bills.

Stiebel Eltron is a company that has been around for many years, and the company’s experience and production values mean their units are extremely reliable. You can expect a Tempra water heater to last for a long time.

As with the Tempra Plus model we looked at above, this is also an extremely quiet unit and is ideal if you don’t want an irritating noisy water heater.

On the downside, this unit doesn’t include the Advanced Flow Control system like the model above. It also lacks the digital display, so there’s no readout telling you how much power the heater is saving for you. These are features found in Tempra Plus models only.

In sum, this is another solid offering from Stiebel Eltron. If you are looking for a reliable water heater from a trustworthy company but don’t need the advanced features of the Tempra Plus range, this is an option that could be worth investigating further.


  • Auto-modulation tech – helps conserve energy
  • Consistent hot water – even if flow rates vary
  • Reliable unit – thanks to Stiebel Eltron’s many years of experience
  • Highly efficient unit – offers around 99% efficiency
  • Silent operation – among the quietest units you can own


  • No digital display – unlike Tempra Plus models
  • No Advanced Flow Control – although still provides continuous hot water

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4. Rinnai V Series HE Tankless Water Heater: Indoor Installation

Rinnai V Series HE Tankless Water Heater

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Rinnai is a well-established company originally founded in Japan that has been making water heaters since the 1960s. It is a company that has long been at the forefront of water heater technology, and this is a gas-powered unit from their range intended for internal installation.

As you would expect from a company with such pedigree, this is a highly efficient heater that can help save you money. Since it is powered by natural gas, it also costs less to run than an electric model.

Depending on the temperature of the groundwater where you live, this heater can allow you to run up to three fixtures simultaneously – this makes it an ideal option for use in any small to medium-sized homes.

Larger models also exist that offer even greater capacity.

It is SCAQMD-approved, giving it strong credentials as a green, clean and efficient heater, and the company offers very generous warranties in case anything should go wrong.

For example, the residential warranty for the heat exchanger is 180 months, for labor, you get 12 months and for parts, the warranty is 60 months.

It is easy to install, and if you have the necessary skills, you should be able to do it yourself.

Something we also like a lot is the fact that it is compatible with the Rinnai app, meaning you can program it, adjust it and check schedules from your smartphone, even when you are away from home.

The main downside is the price since it’s not cheap. However, for such a solid and reliable heater, we still feel it represents great value for money.

Also, it is slightly noisier than some other options because of the exhaust fan. However, this is a minor gripe rather than a deal-breaker.

Overall, there’s a lot to like about this water heater, and if you are looking for a superior-quality option and don’t mind paying extra to get your hands on it, this is a unit that should be on your list of possibilities.


  • High-efficiency unit – helps you save money
  • Compatible with mobile app – can be controlled via smartphone
  • Runs up to 3 fixtures simultaneously – depending on groundwater temperature
  • SCAQMD-compliant – green and clean option
  • Good warranties – you’re covered if anything goes wrong


  • A little noisy – exhaust fan not silent
  • Pricey option – although a high-quality unit

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5. Rinnai V Series HE Tankless Water Heater: Outdoor Installation

Rinnai V Series HE Tankless Water Heater

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This is essentially a very similar unit to the Rinnai heater we just looked at. The only major difference is that this one is designed for external rather than internal installation, so if you are looking to save a little space inside your home, this is the option to go for.

Other than being made to be installed outside, it shares all the same features with the internal model that make that such a great pick.

It is highly efficient – these are heaters from Rinnai’s HE range, which stands for High Efficiency – and is designed to give you hot water on demand while saving you money on gas bills at the same time.

This is a slightly larger model than the one we just looked at, and this one can allow you to use up to five fixtures at the same time, depending on the temperature of your groundwater.

It also has a leak-detection capability that tells the unit if there is a leak and shuts it off to help protect property from damage.

As with the previous model, it can also be connected to Wi-Fi, allowing you to control and program it via the dedicated smartphone app for extra convenience.

Finally, another positive it shares with the internal model is the generous warranty lengths. You get the same residential warranty of 180 months for the heat exchanger, 12 months for labor and 60 months for parts.

On the downside, it also shares the same drawbacks with the internal model. It is not cheap, so if you want something of this quality, you need to be ready to put your hand into your pocket. Also, it’s a little noisy – although this is probably less important if it’s located outside.

If you liked the sound of the Rinnai heater above but want one you can install outside, this could be a great pick. It’s reliable, efficient and easy to operate – a recommended option.


  • Ideal for external installation – save space inside your home
  • Wi-Fi connection possible – can be controlled via smartphone app
  • Use up to 5 fixtures at once – depending on groundwater temperature
  • Generous warranty lengths – for extra peace of mind
  • Leak-detection capability – shuts off to prevent property damage


  • Pricey option – although you expect to pay more for quality
  • Noisy operation – due to exhaust fan

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6. ECOTOUCH Tankless Water Heater  Budget Pick 

ECOTOUCH Tankless Water Heater

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If you need a solution for small-scale heating, for example, heating the water to a single sink, this could be a great budget option that gets the job done.

It is an electric model that is compact and unobtrusive. It has a sleek design and would be ideal to install under or next to a sink to heat the water.

It is highly efficient – it boasts energy efficiency of 98%, making it a good option for heating your water while reducing the bills. The unit itself is also very inexpensive, making it even more attractive if you are looking for a budget-friendly water heater.

We like the way it’s easy to use, too. The front of the heater features a simple digital control panel that’s intuitive to use. This model doesn’t come with a remote control – but another similar version does include one, making it even more practical to use.

At such a low price point, it’s hard to find anything we don’t like about this unit.

We could point out that if you try to use it to heat water for a shower or other more intense applications, you may be disappointed – although it isn’t designed for this, and this is hardly a fair criticism.

Some people might find the quality slightly lacking – however, since it is so affordable, for us, the quality is about what you would expect for the price.

This would be a great option for anyone who is looking for an inexpensive way to heat the water in a single fixture like a sink. If this is what you need it for, then it could be an excellent pick.


  • Inexpensive option – an affordable tankless water heater
  • Ideal for single uses – for example, to heat the water to a single sink
  • Compact and unobtrusive – easy to install anywhere
  • Easy to use – simple and intuitive controls
  • Highly efficient – 98% energy efficiency to help reduce bills


  • Designed for small-scale use – ideal for sinks but not showers
  • Overall quality slightly lacking – but acceptable for a budget heater

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7. Rheem RTEX-18 Residential Tankless Water Heater

Rheem RTEX-18 Residential Tankless Water Heater

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When it comes to reliable water heaters, Rheem is always one of the first brands to be mentioned, and this is an electric tankless model designed for residential use from this well-regarded company.

It features advanced self-modulation technology that adjusts power consumption according to demand. It is highly efficient and can help reduce electricity bills by up to 50%.

It features an attractive design with a digital thermostatic control on the front panel. This allows you to control the temperature of the water with an accuracy of ±1°F.

It’s easy to install, and if you have the necessary plumbing and electrical skills, you can do it without the need to call in a professional. It’s also a compact unit, making it easy to find somewhere it fits.

On the downside, it isn’t cheap – but as with some other models we’ve looked at, you have to expect to pay more for a unit from a top brand.

Also, this model can struggle if you need to use lots of fixtures at the same time or if groundwater is cold – and in these cases, you might be better choosing something more powerful.

All in all, a solid unit from a reputable brand. If this model meets the power requirements for your home, it could be a great pick.


  • Digital thermostatic control – with accuracy of ±1°F
  • Advanced self-modulation – adjusts power consumption according to demand
  • Helps reduce electricity bills – can result in up to 50% savings
  • Compact unit – easy to find space for installation
  • 5-year warranty for heating chamber – and 1-year for parts


  • Expensive unit – cheaper options exist if you’re on a budget
  • Can struggle with multiple fixtures – also if groundwater is cold

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Buyer’s Guide

tankless water heater reviews

Before we look at some of the best units currently available, let’s look at why you would want a tankless water heater and which factors to consider when choosing one.

Why tankless?

Tankless water heaters offer hot water “on-demand”. This means there is no need for water to be kept warm in a tank, wasting energy – the water is simply heated when it’s needed, giving you a constant supply of hot water whenever required.

Tankless heaters are highly efficient, and since you don’t need to waste energy keeping water heated in a tank, switching to tankless can help reduce your bills.

How to choose a tankless heater

tankless water heater

To choose the right tankless water heater for your home, you need to know about the number of fixtures you want to use simultaneously, the corresponding water flow and the temperature of the groundwater where you live.

The number of fixtures refers to how many showers, washing machines, dishwashers and so on you need to use at any one time.

If you only need to use one shower at a time, a smaller heater will be sufficient – but if you need to use multiple showers while also running a washing machine, you will need something more powerful.

The temperature of your groundwater also matters because you need to calculate the temperature rise – i.e. the increase in temperature from the temperature of the groundwater to the temperature you need for your shower etc.

If the groundwater is colder where you live, you will need a more powerful unit since you need to heat the water more for it to reach the required temperature.

Tankless water heater manufacturers provide charts that take into account fixtures, water flow and ground temperature to help you calculate how powerful the unit you require should be.

Other features

tankless water heater feature

Here are a few other features you should consider when choosing a tankless water heater.


How efficient is it? More energy-efficient models will save you more money.


Does it make a lot of noise when in use?

Ease of installation

How easy is it to install? This is important if you plan to install it yourself.


Can it change the level of power consumption according to the demand for hot water? How advanced is this capability? This is an important feature that can help save you money in the long run.

Gas or electric?

Does it run on gas or electricity? A gas unit can be cheaper to run, but this may depend on where you live and the availability of gas there. This is a point to consider when choosing.


How long is the warranty for the water chamber? How about for parts?

Many great options to choose from

As you can see, there are many great options to choose from if you are looking to install a tankless water heater in your home. The key is to understand factors like water flow, fixture and groundwater temperature and then to choose a model with enough power.

If you have decided that tankless is the way to go but you are having trouble making up your mind which model to opt for, any of the units in our review would be a great place to start your search.

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