Best Tankless Water Heaters 2021: A-Z Guide

Best Tankless Water Heaters 2020 - A-Z Guide
Best Tankless Water Heaters 2020 - A-Z Guide
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A tankless water heater might be a great idea for your home. They can save you significant amounts on your utility bills, they last a lot longer than a traditional water tank heating system and they take up less room.

What is a Tankless Water Heater?

Most people are used to water tanks, which can hold a large capacity of water and usually use gas to heat that water all at once so that the home has hot water for sinks, dishwashers, baths, showers and washing machines.

A tankless water heater does the same thing, except without the tank. Instead of heating all of the water and working to keep it hot, the tankless water heater heats water as it goes through the heater. It keeps no water in reserve, but the better systems will heat enough water fast enough that you will always have plenty of hot water for your needs.

What are the Advantages of a Tankless Water Heater?

Tankless water heaters have lots of advantages over water tanks, including:

  • They are much more energy efficient
  • They save money on your energy bill
  • They take up less space, and some can even be installed outside
  • They heat water much more quickly
  • They can last up to twice as long as a water tank heater

What are the Drawbacks of Tankless Water Heaters?

While they might seem like a perfect choice, given all of their advantages, there are a few disadvantages to consider before you make a decision, including:

  • Tankless water heaters can be significantly more expensive
  • They may also be more expensive to install – especially if you are replacing a water tank
  • They may have a lower water output, so your shower may be a little chilly if you are also doing laundry
  • Cheaper or smaller tankless water heaters may not be best for very cold climates

At the same time, if you get a better quality tankless water heater, it should have plenty of hot water for even multiple simultaneous tasks, and it will raise the water temperature enough that it is nice and hot even in the coldest places.

What tankless water heater is best for me?

There are a few basic types of tankless water heaters, including indoor and outdoor, propane, natural gas and electric heating, and different sizes – specifically in reference to how much water, in GPM (gallons per minute), they can heat.

There is also what is called a “point of use” tankless water heater, which is a small, and small output, unit designed not for the whole house but for a single location – like to heat only shower water.

In this buyer’s guide and review of the best tankless water heaters available in 2020, we will look at six different categories:

Our reviews and recommendations come from our own experience, the experiences and feedback of our friends and colleagues, and the reviews and experiences of actual verified customers.

After these reviews, we will give some advice on how to choose a tankless water heater that is best for your home and your needs. 

Once you have done that, you can feel confident that the corresponding unit in our buyer’s guide – Best Tankless Water Heaters 2020: A-Z Guide – will offer the best performance, value and reliability you can possibly get.

What is the Best Large Propane Tankless Water Heater in 2020?

Rinnai RU199EP Propane Tankless Water Heater

Rinnai is a company that shows up on our various buyer’s guides more than almost any other. While their products are not the least expensive, they offer levels of material quality, craftsmanship, reliability and performance that make any Rinnai product quite possibly the best investment you will ever make for your home.

And this Rinnai RU199EP large output propane tankless water heater is no exception.

It is a whole house tankless water heater, with plenty of output for even larger homes – up to 11 gallons a minute, which is more than enough for large families and lots of activities.

With a maximum 199,000 BTU heating power, this Rinnai tankless water heater will work perfectly in any climate, and even though it is an outdoor installation (which will save you space in your home) it is freeze-resistant down to -22 degrees Fahrenheit (about -30 degrees Celsius) and has lots of weather protection features to make sure it will always work when you need it.

Rinnai is an acknowledged leader in heating technology and innovation, and their ThermaCirc360 feature is a great example. It allows the RU199EP to circulate hot water through your house, making sure than even the most distant showers, appliances or sinks have instant hot water and saving you up to 1,100 gallons of water a year!

The Rinnai RU199EP is one of the most energy-efficient tankless water heaters available, with an energy efficiency rating of up to .96 and Energy Star certification. Features like their innovative Dual Heat Exchangers only add to its energy efficiency.

And the RU199EP is a Smart Appliance, meaning it is WiFi compatible and can be monitored and controlled via your phone, tablet or computer.

With the most advanced technology, the most useful features and the best quality available, the Rinnai RU199EP is our choice for best large propane tankless water heater in 2020, and shares the title of best tankless water heater overall with its natural gas sibling, the RU199EN reviewed just below.

Features and Specifications:

  • Tankless Propane Water Heater
  • BTU Range: 15,000 – 199,000
  • Flow Rate: 11 Gallons a Minute
  • Energy Factor: Up To .96 (Uniform Energy Factor .93)
  • Energy Star and Energy Guide Certified
  • WiFi Smart Technology
  • ThermaCirc360
  • Dual Heat Exchangers
  • Warranty: 10 Years Heat Exchanger; 5 Years Parts; 1 Year Labor
Rinnai RU199eP RRU199eP, RU199ep-Propane/11 GPM
19 Reviews
Rinnai RU199eP RRU199eP, RU199ep-Propane/11 GPM
  • ENERGY STAR Qualified with Uniform Energy...
  • Equipped with Rinnai Circ-Logic - Pair with...
  • Save time with hot water whenever and...
  • Save energy and reduce utility costs by...

What is the Best Large Natural Gas Tankless Water Heater in 2020?

Rinnai RU199EN Natural Gas Tankless Water Heater

For the second unit in our list of best tankless water heaters in 2021, we are right back with Rinnai, one of the finest and most innovative companies we have ever encountered.

This time we are looking at the Rinnai RU199EN large output natural gas tankless water, which like the propane version reviewed just above, is also from Rinnai’s top line up Super High-Efficiency Plus series.

It too is a whole house tankless water heater, with plenty of output for even larger homes – up to an amazing 11 gallons a minute, and has the same extremely high maximum 199,000 BTU heating power.

With specs like these, this Rinnai tankless water heater will work perfectly in any climate, and for large homes, large families and lots of activities. It too is meant for outside installation, but like its propane brother has the same freeze-proof features and will be fine in even extreme cold situations.

Rinnai is the acknowledged leader in heating technology and innovation, and their ThermaCirc360 feature is a great example. It allows the RU199EN to circulate hot water through your house, making sure than even the most distant showers, appliances or sinks have instant hot water and saving you up to 1,100 gallons of water a year!

The Rinnai RU199EN is one of the most energy-efficient tankless water heaters available, with an energy efficiency rating of up to .96 and Energy Star certification. Features like their innovative Dual Heat Exchangers only add to its energy efficiency.

And the RU199EN is a Smart Appliance, meaning it is WiFi compatible and can be monitored and controlled via your phone, tablet or computer.

Another brilliant product from the leaders in technology, dependability, performance and customer service, the Rinnai RU199EN is our choice for best large natural gas tankless water heater in 2020, and shares the title of best tankless water heater overall with its propane counterpart, the RU199EN reviewed above.

Features and Specifications:

  • Tankless Natural Gas Water Heater
  • BTU Range: 15,000 – 199,000
  • Flow Rate: 11 Gallons a Minute
  • Energy Factor: Up To .96 (Uniform Energy Factor .93)
  • Energy Star and Energy Guide Certified
  • WiFi Smart Technology
  • ThermaCirc360
  • Dual Heat Exchangers
  • Warranty: 10 Years Heat Exchanger; 5 Years Parts; 1 Year Labor
Rinnai RU199eN RRU199eN, 11 GPM, RU199en-Natural Gas/11
19 Reviews
Rinnai RU199eN RRU199eN, 11 GPM, RU199en-Natural Gas/11
  • ENERGY STAR Qualified with Uniform Energy...
  • Equipped with Rinnai Circ-Logic - Pair with...
  • Save time with hot water whenever and...
  • Save energy and reduce utility costs by...

What is the Best Large Electric Tankless Water Heater in 2020?

Stiebel Eltron Tempra 36 Plus Electric Tankless Water Heater

An electric water heater with enough heating and water flow for larger houses and larger families is a more difficult proposition than a propane or natural gas-powered unit, but the extraordinary, over-engineered Stiebel Tempra 36 is more than up for the job.

While it does not have the extremely high volume of hot water offered by the propane and natural gas heaters above, it should have plenty for even larger homes and families, and even in colder temperatures, the Stiebel Tempra can handle multiple demands at the same time.

Stiebel’s patented Advanced Flow Control means the water will never run cold, and their Variable Flow technology ensures steady temperature even when demand suddenly increases.

These are just some of the many technologies and advanced features you find in a Stiebel Eltron product. The Tempra 36 is engineered and manufactured in Germany and offers a level of quality in materials and construction rarely found in any modern appliance – not to mention one of the best warranties on the market.

Any tankless water heater will probably need installation by a licensed professional, and keep in mind that electric whole-house tankless water heaters all need 240 volt electrical supply, and so you might also need a licensed electrician.

That said, the Stiebel Tempra 36 Plus is substantially less expensive than the gas heaters listed above, and as a result, much, if not all, of that cost, will be offset. And it offers not just the best quality of any electric heater we’ve tried, but the best performance as well, and is the only one we would want in a larger house.

Stiebel Eltron has a slogan that is right to the point: “Simply the Best.” We couldn’t agree more, and especially the Stiebel Eltron Tempra 36 Plus tankless electric water heater, which is our choice for best large electric tankless water heater in 2020.

Features and Specifications:

  • Tankless Electric Water Heater
  • Maximum Temperature Increase: 55 Degrees Fahrenheit
  • Flow Rate: Up To 7.5 Gallons a Minute
  • Self Modulating Energy Technology
  • Advanced Flow Control
  • All Copper Internal Tanks and Tubing
  • Made in Germany
  • Warranty: 7 Years Water Tank; 3 Year Parts
Sale
Stiebel Eltron Tankless Heater – Tempra 36 Plus – Electric, On Demand Hot Water, Eco, White
753 Reviews
Stiebel Eltron Tankless Heater – Tempra 36 Plus – Electric, On Demand Hot Water, Eco, White
  • On-demand, continuous and unlimited supply of...
  • Sleek design saves space and no venting...
  • Electronic switch activated for virtually...
  • Copper sheathed heating element housed in...
  • 7 Years leakage and 3 years parts complete...

What is the Best Medium Propane Tankless Water Heater in 2020?

Rinnai RL75IP Natural Gas Tankless Water Heater

At the risk of sounding like a broken record, in our buyer’s guide and review of best tankless water heaters on the market today we go again to Rinnai for both our Propane and Natural Gas tankless water heaters for medium to small homes.

Rinnai is clearly the best company we know, and offers the best products in their field – they have, after all, been doing this for over a hundred years, and have been innovating and improving the whole time.

The Rinnai RL75IP is a smaller output tankless water heater, but still puts out a strong 7.5 gallons a minute of hot water, and has an extremely high maximum BTU output for its class – up to 180,000 BTU. 

Meant for indoor installation, the Rinnai RL75IP is surprisingly small and will take up hardly any space, and with advanced Circ-Logic recirculating capabilities and a high energy efficiency rating of 0.82, it is one of the most energy-efficient propane tankless water heaters on the market and will save you plenty of money as well – as compared to a traditional tank heater or even other tankless heaters.

And the RL75IP is a Smart Appliance, meaning it is WiFi compatible and can be monitored and controlled via your phone, tablet or computer.

If you know the tankless water heater market (or the domestic heating market in general) the name Rinnai is enough of an endorsement in itself, and you would purchase any of their products without hesitation, and know you are getting the best performance, quality and value possible.

We do know the market, and we have tried lots of their products, as well as lots from many other manufacturers, and we have no doubt whatsoever that the Rinnai RL75IP Propane Tankless Water Heater is the best medium-sized propane tankless water heater in 2020.

Features and Specifications:

  • Tankless Propane Water Heater
  • BTU Range: 10,300 – 180,000
  • Flow Rate: 7.5 Gallons a Minute
  • Energy Factor: .82 (Uniform Energy Factor .81)
  • WiFi Smart Technology
  • Circ-Logic Water Circulation
  • Warranty: 10 Years Heat Exchanger; 5 Years Parts; 1 Year Labor
Rinnai RU199eN RRU199eN, 11 GPM, RU199en-Natural Gas/11
19 Reviews
Rinnai RU199eN RRU199eN, 11 GPM, RU199en-Natural Gas/11
  • ENERGY STAR Qualified with Uniform Energy...
  • Equipped with Rinnai Circ-Logic - Pair with...
  • Save time with hot water whenever and...
  • Save energy and reduce utility costs by...

What is the Best Medium Natural Gas Tankless Heater in 2020?

Rinnai RL75IN Natural Gas Tankless Water Heater

As mentioned just above, Rinnai is our strong choice for both our Propane and Natural Gas tankless water heaters for medium to small homes, not to mention large homes and families – an unprecedented 4 recommendations out of 7 total in our 2020 buyer’s guide and review of best tankless water heaters.

Rinnai is clearly the best company we know, and offers the best products in their field – they have, after all, been doing this for over a hundred years, and have been innovating and improving the whole time.

The Rinnai RL75IN is a smaller output tankless water heater, but still puts out a strong 7.5 gallons a minute of hot water, and has an extremely high maximum BTU output for its class – up to 180,000 BTU, plenty for any climate or conditions. 

Meant for indoor installation, the Rinnai RL75IN is surprisingly small and will take up hardly any space, and with advanced Circ-Logic recirculating capabilities and a high energy efficiency rating of 0.82, it is one of the most energy-efficient natural gas tankless water heaters on the market and will save you plenty of money as well – as compared to a traditional tank heater or even other tankless heaters.

And the RL75IN is Smart Home ready, responding to voice command, compatible with your WiFi and able to be monitored and controlled via your phone, tablet or computer.

If you know the tankless water heater market (or the domestic heating market in general) the name Rinnai is enough of an endorsement in itself, and you would purchase any of their products without hesitation, and know you are getting the best performance, quality and value possible.

We do know the market, and we have tried lots of their products, as well as lots from many other manufacturers, and we have no doubt whatsoever that the Rinnai RL75IN Natural Gas Tankless Water Heater is the best medium-sized natural gas tankless water heater in 2020, and yet another outstanding Rinnai product.

Features and Specifications:

  • Tankless Natural Gas Water Heater
  • BTU Range: 10,300 – 180,000
  • Flow Rate: 7.5 Gallons a Minute
  • Energy Factor: .82 (Uniform Energy Factor .81)
  • WiFi Smart Technology
  • Circ-Logic Water Circulation
  • Warranty: 10 Years Heat Exchanger; 5 Years Parts; 1 Year Labor
Rinnai RU199eN RRU199eN, 11 GPM, RU199en-Natural Gas/11
19 Reviews
Rinnai RU199eN RRU199eN, 11 GPM, RU199en-Natural Gas/11
  • ENERGY STAR Qualified with Uniform Energy...
  • Equipped with Rinnai Circ-Logic - Pair with...
  • Save time with hot water whenever and...
  • Save energy and reduce utility costs by...

What is the Best Medium Electric Tankless Heater in 2020?

Rheem RTEX-24 Electric Tankless Water Heater

It seems pretty simple to us. Even in this smaller range, a tankless water heater is a major investment and something you will have in your home, use and depend on for many, many years. 

As such, we see great wisdom in sticking with the most respected companies in the industry, established leaders in product quality, innovation and performance. This is why Rheem, along with Rinnai and Stiebel Eltron, is such a frequent recommendation in Know the Flo’s buyer’s guides and reviews and is represented in our 2020 list of the best tankless water heaters.

And for small to medium-sized homes, smaller families and milder climates, the Rheem RTEX electric tankless water heater is an obvious recommendation.

The Rheem RTEX-24 has the most advanced water modulation system on the market and will deliver consistently hot water even with rapidly changing demands. This system, along with an advanced digital thermostat, superior heating elements and many other factors lead to an impressive 99.8% energy efficiency rating.

The RTEX24 will provide up to 6 gallons a minute of hot water, and can increase water temperature by up to 65 degrees Fahrenheit – excellent performance for its price and class.

Meant for inside installation, this Rheem tankless electric water heater is quite small – 18 by 19 inches and only 4 inches deep – and is ultra-easy to install. If you want to try this as a DIY project, though, keep in mind that whole-house tankless electric heaters do require 240-volt power, and so you may need a licensed electrician.

There are few, if any, electric heaters that can match this one, in terms of performance and specifications, and even less that can offer the energy efficiency, the reliability and material quality, or the outstanding reputation that the RTEX24, or any Rheem product, has.

And, at its surprisingly low price, the Rheem RTEX-24 Electric Tankless Water Heater offers an almost unbelievable value and is an easy choice for Best medium electric tankless water heater in 2020.

Features and Specifications:

  • Tankless Electric Water Heater
  • Maximum Temperature Increase: 65 Degrees Fahrenheit
  • Flow Rate: Up To 6 Gallons a Minute
  • All Copper Immersion Chamber with Brass Fittings
  • Digital Temperature Display and Thermostat
  • Advanced Water Modulation System
  • Warranty: 5 Years
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater, Gray
291 Reviews
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater, Gray
  • ON/OFF Dial Control with adjustable digital...
  • Self-modulating power control
  • 24kW Model Flow Rate: up to 5.9 GPM for...
  • Bottom 3/4" NPT water connections
  • On demand, consistent and continuous hot...

What is the Best Point of Use Tankless Water Heater in 2020?

EcoSmart ECO 11 Electric Tankless Water Heater

If you don’t want to provide hot water for your whole house, but just in a single place – a shower, a sink or a washing machine, for example – a Point of Use tankless water heater is a perfect choice.

And the best one we’ve found is the EcoSmart ECO-11, a well-built unit that is ultra-simple to install and to use, with digital temperature control, precise energy management features and a limited lifetime warranty.

With a much lower water flow than any of the whole-house tankless water heaters above, the EcoSmart ECO11 can heat up to 2 gallons of water a minute, which is plenty for one or two sinks, a shower or other single-use applications. In fact, you can probably heat an entire bathroom’s water with this one heater.

By allowing your larger water heater to work less, and just heating water as you need it, the ECO 11 can save you considerably on utility bills. And, with its patented Self-Modulating technology, this EcoSmart point of use tankless water heater has an astonishingly high 99.8% energy efficiency rating, saving you even more – and helping to save the planet as well.

A simple, high-quality unit that offers great performance and exceptional energy efficiency, and should offer many years of trouble-free service, the EcoSmart ECO 11 Electric Tankless Water Heater is our choice for the best point of use tankless water heater in 2020.

Features and Specifications:

  • Tankless Electric Point of Use Water Heater
  • Flow Rate: Up To 2 Gallons a Minute
  • Digital Temperature Display and Thermostat
  • Patented Self-Modulation Technology
  • Warranty: Limited Lifetime
Sale
EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology
2,492 Reviews
EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology
  • Lifetime warranty
  • Save up to 60-percent on your water heating...
  • Never run out of hot water with an ECOSMART...
  • Patented Self Modulating Technology and...
  • ECOSMART tankless water heaters are...

How do I Choose the Right Tankless Water Heater?

If you are building a house, planning a major renovation, replacing a broken water tank heater or just want to save on your heating bills, you probably have already decided on a tankless water heater.

But which tankless water heater?

The brand and model are easy – the choices above represent the finest companies and the most advanced, high performance, reliable tankless water heaters on the market today.

All you have to do is decide how much hot water you need, click the corresponding link and you will have the best unit possible delivered to your home.

How Much Hot Water do I Need?

This is determined with a simple GPM (gallons per minute) calculation, using the following guidelines:

  • A sink faucet will use around .5 GPM of hot water.
  • A dishwasher will use around 1.0 GPM of hot water.
  • A clothes washer will use around 2.0 GPM of hot water.
  • A shower will use around 2.5 GPM of hot water.
  • A bathtub will use around 4.0 GPM of hot water to fill (but, of course, you can fill it more slowly).

If you have an idea of how many of these items you may be using at the same time – that is, will more than one person be taking a shower at once, or will you have the shower, clothes washer and dishwasher running simultaneously – then you can get an idea of the maximum GPM of hot water your new tankless water heater should provide.

  • Our large tankless water heaters provide 7.5 to 11 GPM of hot water.
  • Our medium tankless water heaters provide 6 to 7.5 GPM of hot water.

Regardless of your use, you probably don’t want less than 6 GPM for a whole-house tankless water heater.

Another way of figuring this out is based on the size of your family and your home.

  • If you have a large house (2,500 square feet or larger), regardless of family size and use, you probably want a large tankless water heater.
  • If your house is smaller than 2500 square feet, you are fine with a medium-sized heater.
  • If you have 4 or more people in your family, excluding infants, you probably want a large tankless water heater – even in a smaller house.
  • If you have 3 or fewer people, and a smaller house, again you should be fine with a medium-sized tankless water heater.

Whatever you determine, it is good to remember that – while you never want to spend more money than necessary – you can’t go wrong getting a little more capacity than you need. So if you are unsure (or if you have children who are approaching their teens!) you might want to get a larger unit – it might even save you money in the long run.

Along those lines, our affiliate links will often lead you to the best prices you can get, but you might also notice that, for many of our recommendations, the Amazon page also has links leading to different sized models of the same unit – offering more or less GPM of hot water.

The different models in the same line – especially with industry-leading brands like Rinnai, Stiebel Eltron, Rheem or that young upstart EcoSmart, will always be great choices and can be purchased with just as much confidence, and ultimately will provide just as much satisfaction, as our primary recommendations.

We hope that Know the Flo’s latest buyer’s guide – Best Tankless Water Heaters 2020: A-Z Guide – has been a great help in your selection process, and that you will turn to us again in the future!

James McWhirter
James McWhirter
Hey! I'm James. I like to share my love for technology and all things tech-related. With previous experience working as an editor at a newspaper, I now help knowtheflo.com with content production and of course, test out few products myself!

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