Best Tankless Water Heater Reviews 2021

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Tankless water heaters, or continuous flow water heaters, are taking North America by storm.

Okay, perhaps that’s a bit of an overstatement.

A more accurate explanation is they’re steadily gaining popularity — and with good reason. One of the major reasons being that tankless water heaters can actually save you money!

That’s right — despite the higher upfront price, a tankless water heater can save you an average of $108 per year in energy costs. These savings grow exponentially when you use the heaters from our best tankless heaters list.

And energy savings aren’t all you stand to gain.

Let’s take a closer look at some of these benefits and figure out the best tankless water heater for you.

But first, we have to understand what a tankless water heater is.


What is a Tankless Water Heater?

Tankless water heaters are powerful instant heating devices that warm water as it flows through them.

They are referred to as “tankless” because they don’t retain water within the unit. Instead, they use copper heat exchangers to heat water as it flows through the machine.

The heating is usually done either through an electric element or a gas burner.

How Does a Tankless Water Heater Work

Additionally, tankless water heaters only work on demand. When you turn on your tap, cold water flows into the unit, where it gets heated. Then hot water flows out through the spout.

The Best Tankless Water Heaters

Now that you know what a tankless water heater is and what to consider when picking one, you are ready to hit the shops.

To help you along, here are our top recommendations for the best tankless water heaters:

The Best Tankless Water Heaters: Quick Take

Best Overall Tankless Heater

Rinnai RUC98iN Ultra Series
Rinnai RUC98iN Ultra Series
Features Weight: 82 lbs.

Dimensions: 10” x 18.5” x 26”

Voltage: 120 volts

Flow rate: 9.8 gallons per minute

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Best Electric Tankless Water Heater

Stiebel Eltron Tankless Heater – Tempra 36 Plus
Stiebel Eltron Tempra 36
Features Weight: 19 lbs.

Dimensions: 4.63” x 16.63” x 14.5”

Voltage: 208 volts

Flow rate: 7.5 gallons per minute

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Best Gas Tankless Water Heater

Takagi T-KJr2-IN-NG Indoor Tankless Water Heater
Takagi T-KJr2-IN-NG
Features Weight: 37 lbs.

Dimensions: 6.7” x 13.8” x 20.3

Voltage: 120 volts

Flow rate:  6.6 gallons per minute

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Best Portable Tankless Water Heater

Eccotemp L5 Portable
Eccotemp L5 Portable
Features Weight: 11.2 lbs

Dimensions: 11.4” x 4.8” x 15.9”

Voltage: 3 volts

Flow rate:  1.5 gallons per minute

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Best Point of Use Tankless Water Heater

Ecosmart POU 6
Ecosmart POU 6
Features Weight: 4 lbs.

Dimensions: 11” x 3” x 6”

Voltage: 220 volts

Flow rate: 1.5 gallons per minute

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Factors to Consider When Picking a Tankless Water Heater

Instant access to hot water and a reduced energy footprint are pretty compelling points to drive you to action.

However, a lot more than only this goes into selecting the best tankless water heater.

Here’s everything you need to keep in mind when making your decision:

1. Type of Fuel

There are three main types of fuel for tankless water heaters:

II. Natural gas

Natural gas costs a lot less than electricity, making gas-powered heaters better long-term investments, even despite the higher initial costs.

Natural gas is also a better choice for high-demand homes. Gas models operate at higher power output and heat more cold water to the ideal temperature at a lower cost.

However, gas units are a poor choice for mobile homes because natural gas is not easily stored.

Additionally, if you don’t already have a natural gas line to your home, the connection cost might be high for your budget.

You can check out the best gas water heaters here.

II. Electricity

An electric tankless water heater is comparatively cheaper in initial and installation costs. However, the high consumption rate and cost of electricity nullify this slight edge.

The power requirements are sometimes so high, older homes are unable to meet the demand.

Check that your home meets the power requirements before purchasing an electric tankless water heater. If not, a costly electrical system upgrade may be necessary.

You can check out the best electric tankless water heaters here.

III. Propane

Propane gas is the most expensive of the three options. It’s often not piped into a home — instead, a portable fuel tank powers the tankless water heater.

This makes propane-powered heaters less practical for home use but ideal for mobile homes and recreational use.

Note: Propane and gas powered tankless heaters are often interchangeable.

You can check the best propane water heaters here.

2. Flow Rate

Flow rate refers to the maximum volume of hot water your heater is capable of producing. It’s measured in gallons per minute (GPM).

Each fixture inside your home needs a certain level of flow (GPM) to operate as expected.

For example, a bathroom tub needs about 4 GPM while a shower needs about 3 GPM.

To determine the necessary flow rate for your home, consider the total amount of hot water used within the house simultaneously.

A lower flow rate (3 to 5 GPM) will suffice if you hardly ever use different fixtures at once. However, opt for a higher flow rate water heater (7.5 to 8 GPM) if multiple concurrent uses are likely.

Use the chart below to work out your household’s total average GPM requirement:

Average Flow Rate (GPM)
Shower 1.0 – 2.5
Bathtub 2.0 – 4.0
Bathroom Sink 0.5 – 1.5
Laundry machine 1.5 – 3.0
Kitchen Sink 1.0 – 2.5
Dishwasher 1.0 – 2.5

Add up the necessary fixtures to get an overview of your total tankless water heater GPM needs.


  • Whole-house tankless water heaters are larger and more powerful. They are capable of providing the entire home with hot water. They also have much higher flow rates and power outputs.
  • Point-of-use tankless water heaters are better suited for single fixtures. They are a great option if you can afford multiple heaters.


3. Power Input

Power input refers to the energy required to heat water to a specified temperature.

It’s measured in British Thermal Units (BTUs), where 1 BTU is the amount of energy it takes to heat one pound of water by one Fahrenheit.

To determine your optimal power input, consider the groundwater temperature in your area. Unlike traditional water heaters, groundwater temperatures affect tankless water heaters.

For instance, a tankless model that provides 8 GPM in a warm area might only manage about 4.5 GPM in a cold area. This is because the colder water will need the temperature raised by much more.

Use your coldest groundwater temperature to calculate your power input.

average groundwater temperatures in USA

For example:

If the groundwater temperature in your area is 40°F, and you would like your hot water at 120°F, your heater needs to increase the water temperature by 80°F.

To do so, it will need 667 BTUs per gallon.

If your shower runs at 2.5GPM or 150 gallons per hour, to heat that 150 gallons from 40°F to 120°F, your tankless water heater would need to produce 100,000 BTUs per hour. (Assuming 100 percent efficiency and that only one fixture is in use.)

However, if efficiency drops or you introduce another fixture, then the BTU requirement goes up.

The formula to work this out is:

[500 x GPM x Temp. Change= Required Power Input (BTU per Hour)
Efficiency Percentage

This means 500 is the rounded up (499.8) weight of a gallon of water (8.33 lbs.) multiplied by 60 minutes.

4. Energy Efficiency

Unlike a standard heater, a tankless water heater does not consume a lot of electricity — in fact, it’s specifically designed to save on energy consumption.

When shopping for a tankless water heater, look for a unit that delivers the best efficiency. One way to ensure this is by looking for an Energy Star rating on the product.

Additionally, you can also look for the Universal Efficiency Factor (UEF). The higher the number, the higher the efficiency of the system — and your savings.

Related: Pros and Cons of Tankless Water Heaters

5. Reliability

Contrary to popular belief, large brands don’t necessarily make the best tankless water heaters.

It’s not uncommon to find well-established brands that would prefer to continuously replace their product rather than improve its longevity.

Consider customer ratings and after-sale services when selecting a tankless water heater. Most importantly, stick to products and brands with at least four out of five-star ratings.

6. Price

Tankless water heaters come with different features at different price points.

Before investing, consider your budget. Otherwise, you might end up blowing money on features you don’t need.

Also, keep in mind that the price of a tankless water heater does not always denote quality. Cheaper models might offer savings on upfront costs but end up being less durable.

Similarly, a large, expensive water heater might be wasted on your simple hot water needs.

A good rule of thumb is to let your needs dictate your choice — how you use the unit is what determines whether the tankless water heater is worth the purchase.

1. Best Overall Tankless Water Heater: Rinnai RUC98iN Ultra Series

Rinnai RUC98iN Ultra Series

With almost a century of experience in the market, Rinnai isn’t new to the water heating game.

This is evident in the RUC98iN Ultra, and that is why it’s our top pick for the best tankless water heater.

It’s packed with advanced technology that makes it super-efficient, and the tech also ensures a steady and consistent supply of hot water — no matter where you live.

Another key feature is the built-in Wi-Fi that allows you to monitor and change settings.

However, all this tech is just the cherry on top. What truly sets the RUC98iN apart is the powerhouse 9.8 GPM.

No matter the size of your home, or your hot water needs, this heater has you covered!

Okay, I waited to send in this review because I am a first-time tankless user. We are a family of 5 and use LOTS of hot water. We replaced our 80-gallon tank 3 times in 15 years. Since we can’t get an 80 any longer, we went the tankless route. I could not be happier! The benefits are definitely being noticed. Small footprint (much more room in my storage area now), unlimited hot water – can’t say how much that means to 4 girls!! We have not once noticed any issues with having enough even with a couple of showers going at the same time.” — Garrett Smith


  • Low NOx emissions
  • Up to 0.96 energy factor
  • Compact, space-saving design
  • 95% thermal efficiency
  • 199,000 BTU


  • Requires additional OEM parts for the concentric exhaust
  • It’s expensive

2. Best Electric Tankless Water Heater: Stiebel Eltron Tempra 36

Stiebel Eltron Tankless Heater – Tempra 36 PlusStiebel is among the foremost water heater manufacturers with some of the best heaters on the market. The Eltron Tempra 36 is no exception.

Granted, at about $900 it’s a bit pricier than most other options. But it’s well worth it, especially if you live in an area with a low ground-water temperature.

Even at freezing temperatures, the Tempra 36 can raise the water temperature by up to 105°F while still putting out 3.6 GPM.

In areas where the necessary water temperature rise is about 40°F, it’s a champ — it puts out a whopping 7.5 GPM.

These figures are impressive for any tankless unit, but even more so for an electric tankless water heater.

Here’s what a happy Stiebel Tempra 36 user had to say about his experience with the water heater:

I did a LOT of research on tankless before installing this one last weekend.

We live just north of Seattle and installed the 29 plus model for whole-house use. The water inlet temp in my region is around 45°F. This thing has no issues providing 114-degree water to my shower while in the 116-degree setting.” — Sam


  • Most technologically advanced heater
  • 15–20% more energy efficiency
  • No venting is required


  • Requires professional installation
  • Not budget-friendly

3. Best Gas Tankless Water Heater: Takagi T-KJr2-IN-NG

Takagi T-KJr2-IN-NG Indoor Tankless Water Heater

The Takagi T-KJr2-IN-NG is the smallest tankless water heater from Takagi. But don’t let that dissuade you — this compact unit is more than capable of supplying unlimited hot water to your whole house with no trouble.

At $520, it’s also very reasonably priced for the performance — up to 6.6 GPM for a unit measuring 6.7″ x 13.8″ x 20.3″.

And let’s not forget the 10-year heater exchange warranty.

But you don’t need to take our word for it. Here’s what a happy user had to say:

I’m very impressed with this unit. It receives 5-stars from me as it’s both affordable and, so far, dependable. Dependability is my #1 concern as you learn just how deeply you depend on the water heater once it goes out. Pleased to say this one has lasted 14 months and is still going strong.” — bf123

Related: Best Propane Tankless Water Heaters Reviews


  • Very compact
  • Most versatile unit
  • Easy on the wallet
  • Enhanced safety design


  • Requires professional installation
  • Unsuitable for large homes

4. Best Portable Tankless Water Heater: Eccotemp L5 Portable

Eccotemp L5 Portable

You’d be forgiven for wondering what this water heater is doing on the list; it’s outclassed by most of the other heaters.

The answer is simple: Price and Portability.

You’d be hard-pressed to find a tankless water heater, gas or electric, that gets the job done for less than $600.

The Eccotemp L5 gets the job done at a shockingly low price of $120.

This is why the Eccotemp is a best selling portable tankless water heater — it’s the most practical choice for cabins, campsites, and even your home for emergencies.

The heater has an adequate 1.5 GPM flow capacity and manual temperature adjustments. It also has automatic electric ignition when the water starts flowing through it.

In truth, there’s no other heater that can generate 37.5K BTUs worth of hot water in such a compact unit. That’s what makes the Eccotemp L5 such a steal.

And we’re not the only ones who think so:

This performed just as expected. This is the third or fourth one of these I have purchased. I give it five stars because I know its limitations, and it works perfectly for what I need. I use it as an outdoor shower and love it, but you want to make sure you take it inside as soon as it starts getting really cold outside. The copper tubing is very thin and will crack if water freezes inside.” — Lisa W.


  • Perfect for outdoor showers
  • Works with most showerheads and hoses
  • Easy to set up and use


  • Can only support one fixture at a time
  • No visual thermostat

5. Best Point of Use Tankless Water Heater: Ecosmart POU 6

Ecosmart POU 6

Ecosmart POU 6 is a brilliant tankless water heater with innovative engineering and a reasonable price. It’s a great choice if you’re looking for a compact point of use water heater that won’t break the bank.

The heater is best suited for low flow rates, perhaps at around one gallon per minute. However, it’s still quite capable of slightly higher GPMs.

At 35°F, the Ecosmart POU 6 can deliver up to 1.07 GPM, while at 65°F, it will deliver around .58 GPM.

Additionally, the compact design makes it easy to install anywhere in your home. Here’s what a long-term Ecosmart POU 6 user had to say about their unit:

I have mine under my kitchen sink and ran a line to an outdoor shower by the pool. No longer any cold water showers before going in my pool and getting out. My shower runs about 1.5 GPM, and it was a toasty 118 coming out of the shower. Had to remove the restrictor, and it now comes out about 105 degrees on full blast. At the sink and to the dishwasher, it has no problems heating up to 130 degrees.” — Robert Snyder


  • Small, compact, and lightweight
  • Great for single fixture use
  • Digital display for temperatures
  • Stainless steel heat exchanger


  • No internal thermostat
  • Unsuitable for cold areas
  • Warranty only valid with professional installation

Related: Best Point of Use Water Heaters Reviews

Hot water is a basic need in any home, and this is what makes selecting the right water heater for your needs essential.

However, with so many options to choose from, picking the right one for you is often easier said than done.

But not anymore, thanks to Shower Insider — your ultimate one-stop water heater review site.

At Shower Insider, we are committed to bringing you honest, unbiased reviews on everything water heating. All our reviews are based on real people’s data and their experiences.

So, if you’re in the market for anything water heater related, look no further than Shower Insider.

The Pros and Cons of Switching to a Tankless Water Heater

If the idea of constantly heating your water in a big conventional tank sitting in your basement or garage sounds mighty inefficient and wasteful to you, then a tankless water heater may be the right option for you. The idea is that it heats the water as you need it instead of continually heating water stored in a tank. So, If you’re considering making the switch, you should carefully weigh the pros and cons first. To make it easier for you, we have researched some of the advantages of a tankless system, alongside some of the compromises related to the compact, more energy efficient option.

Advantages of Using a Tankless Water Heater

There are many advantages to switching: From increased energy saving and reduced operating costs to space savings and extended lifespan, find out more about what makes for good reasons to upgrade.

  • Comfort and convenience : There’s no two ways about it : Tankless water heater perform much better than the traditional tank heating systems. They take up much less space and provide you with an unlimited amount of hot water. When you are using one, you’ll say goodbye to compromising on hot water usage, or scheduling your family’s bathing times.
  • Eco-friendly with on-going cost savings : One of the few downsides of making the switch, is the big money sink that goes into the water heater – if you really want to get a good one, you have to shell out some serious dough. However, while tankless water heaters are a relatively pricey upfront expenditure, their operating costs down the line should start to make up for it. Unlike traditional tank heating systems, these products are cost-effective, so you’re saving in not having to spend money on standby heat, meaning you’re not wasting money heating water in a big tank that’s just sitting idly waiting for someone to need hot water. To the contrary, tankless units operate only when there is a demand for hot water, so there’s no energy wasted on heating unused water. This will reduce energy costs by as much as 35% a year.
  • Long lifespan & Reliability : Tankless heaters last about five to 10 years longer than a tank heater. They are estimated to last up to 20 years, compared to tradional tank water heaters that are supposed to last between 10 to 15 years. With that said, if you are planning on staying in one home for many years, that’s a hefty replacement cost you’re saving.
  • Space Savings : Even if you weren’t concerned neither about saving money nor about energy efficiency, one of the biggest, yet most important advantage of going tankless is the the potential space savings. Traditional ones are bulky. I mean think about that big tank of 40 to 60 gallon capacity measuring at the very least around 60″ tall and 24″ wide. That bulky metal tank can take up precious real estate in a home where space is at a premium. A tankless one, in comparison, might be the size of an ordinary medicine cabinet, meaning you can install it in very tight spaces such as as closet or even under a sink.
  • Safe and Clean : Another area in which the demand water heater – score high is safety. First Of all, with tankless you avoid using water that has been stored in a tank with accumulated rust and scale. Additionally, and unlike the storage type that keep gallons and gallons of water heated twenty-four hours a day, seven days a week, water heater units safety is due to the fact that they only operate when hot water is needed. Some of the latest tankless water heaters aren’t afraid to push the enveloppe, they come with several innovative features which boost their safety. For example, some high-end models are fitted with monitoring systems that provide details about water pressure and flow. And in case of failure, the heater turn off instantly.

Disadvantages of Using a Tankless Water Heater

While they might sound like a no brainer, there are several reasons why opting for them might not be for anyone.

  • Limited Water Output : A traditional big tank water heater that stores up 60 gallons of hot water at a time will feed your showers, laundry and faucets  with sufficient hot water for quite some time. Additionally, the moodern tanks reheat additional water supply quite quickly as well, so you’ll litteraly never run out of hot water when you need it. Whereas, A tankless one has very limited output and it’s only able to provide a few gallons of hot water at all times but also at a time. That said, if you are living in a big house and have large family, and everyone’s taking a shower, doing the laundry and dishes at the same time, a tankless one might not be up to the task or suitable for your family’s particular needs.
  • Hefty Upfront Cost : One of the few downsides of making the switch is the big money sink that goes into the tankless water heater. It will cost you twice as much as conventional tank water heater. Additionally, and unlike conventional storage tanks, retrofitting a home with a tankless unit isn’t an easy task, and it can be extremely difficult and costly. So, you’ll need a skilled plumber to do the job. Bear in mind that water heaters require good venting which can be costly.

Traditional tank water heaters VS Tankless Water Heaters – Summary


Type How it Functions Factors to Consider
Conventional Tank Almost permanently on – stores constantly heated water.
  • Economical
  • Can be positioned in closet, basement or garage
  • Capacity ranges from 40 – 60 gallons
  • Takes large space.
Tankless Heats cold water with a gas burner or electric elements as it passes through the heat- exchanger
  • Requires larger up-front investment
  • Hangs on wall and frees up floor space
  • Excellent for part-time occupied residences
  • Can run out of water during heavy usage
  • Requires ventilation