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Best Tankless Water Heaters

To find the best tankless water heater, we reviewed:
  • 1. Performance
  • 2. Capacity
  • 3. Cost
  • 4. Uniform Energy Factor (UEF)
  • 5. Lifespan
  • 6. Warranty
Best tankless water heater graphic featuring a guy in a rethority shirt pointing at a tankless water heater and smiling

Disclaimer: REthority is supported by ads and participation in affiliate programs. We may earn a commission when you click our links. The information included in this post is for informational purposes only and should not be taken as legal or financial advice.

Tankless water heaters are affordable and efficient. But more importantly, you can put them almost anywhere. Let’s take a look at the five best tankless water heaters on the market today.

These are graded according to our scale that accounts for performance, capacity, cost, energy efficiency, lifespan, and warranty. We’ve chosen the five models that provide the best balance of all these factors.

Best Overall

Rinnai RU199iN Sensei Super High Efficiency Tankless Water Heater, 11 GPM - Natural Gas: Indoor Installation

Rinnai RU199iN Super High-Efficiency Tankless Water Heater

While expensive, this unit offers the best performance of all units we reviewed.

The Rinnai RU199iN Gas Tankless Water Heater is an impressive unit. It has the highest performance level of any of the tankless units in our list (11 GPM), extended capacity for up to 7 fixtures at once, and a jaw-dropping 199,000 BTUs to ensure there’s always plenty of hot water. Energy-efficient, powerful, long-lasting, and still affordable, this is our number one tankless water heater pick. 

Overall Score: 29/30

Performance: 5/5

This model has a Flow Rate of 11 gallons per minute (GPM) and a max of 199,000 BTUs, making it a super-efficient, high-performing unit. Customers give it an average of 4.6 out of 5 stars. 

Capacity: 5/5

Pumping out up to 11 gallons per minute of hot water enables this model to supply a household of 5+ people. It can deliver hot water to up to 7 fixtures at once, so you never have to worry about running out. 

Cost: 4/5

The only place this unit doesn’t shine is the higher-end price. At $1,500, on average, it is about $500 above the average cost for a tankless water heater. However, it’s also above average in every other regard – performance, capacity, energy efficiency, and warranty, so it seems to be well worth it. 

Energy Efficiency: 5/5

This model is very energy efficient, especially for a natural gas unit. Expect 93% to 96% energy efficiency with very little standby energy loss from this model. 

Lifespan: 5/5

This unit’s lifespan may be up to 20 years, though the warranty doesn’t fully cover that. Rinnai says it should easily last 20 years. 

Warranty: 5/5

Rinnai offers a factory warranty of 10 years on the heat exchanger, one year on labor, and four years on parts and components. This ensures you’re protected for a long period should anything need to be replaced. 


Rinnai RU180iN Sensei Gas Tankless Water Heater

A great all-around option for those seeking performance, price, and lifespan.

The Rinnai Sensei gas tankless water heater is a great all-around option for anyone who wants to balance the unit’s cost, performance, energy efficiency, and lifespan. You get all of the above with the high-efficiency Sensei model. It offers up to 180,000 BTUs, 10 gallons per minute Flow Rate, condensing, and recirculation technology. 

Overall Score: 29/30

Performance: 5/5

This model has a 10 gallon per minute (GPM) Flow Rate, a maximum of 180,000 BTUs, and features like the Circ-Logic technology for performance-boosting recirculation. It has an average of 4.6 out of 5-star reviews. 

Capacity: 5/5

The 10 GPM Flow Rate makes this model appropriate for a household with up to 5 people. It has enough capacity to deliver hot water to multiple taps at once.

Cost: 4/5

The cost of this unit is about $1,375. This is slightly above average, considering that whole-house tankless models run somewhere in the $1,000 range. 

Energy Efficiency: 5/5

This model has a 93% energy efficiency rate. Compared to other gas tankless units, this is average. Compared to electric units, it is slightly lower. 

Lifespan: 5/5

Rinnai says this tankless model has a lifespan expectancy of about 20 years. This is the high end of average for tankless units. 

Warranty: 5/5

You’ll get a factory warranty for ten years on the heat exchanger, one year on labor, and four years on parts. 


Rinnai RUR98iN Ultra Series Condensing Indoor Natural Gas Tankless Water Heater, 9.8 Max

Rinnai RUR98iN Ultra Series Condensing Gas Tankless Water Heater

Cut down on electricity bills with a solid tankless natural gas water heater.

The Rinnai RUR98iN is part of their Ultra Series. This model uses natural gas instead of electricity, so it is slightly less energy efficient because it keeps the pilot light burning at all times. However, it is still one of the most energy-efficient water heaters available.

With special features like recirculation technology for endless hot water, a higher than average flow rate, and condensing technology that further increases efficiency, this is one of the best tankless options on the market. 

Overall Score: 27/30

Performance: 5/5

This model is capable of providing up to 9.8 gallons per minute (GPM) of hot water. It’s a gas water heater, so its level of performance is higher than electric models. It’s even WiFi capable. Customer reviews give this model 4.2 out of 5 stars, indicating a higher than average performance level. 

Capacity: 5/5

The Flow Rate is 9.8 gallons per minute (GPM) at a temperature rise of 70 degrees (assuming the cold water it heats is 50 degrees Fahrenheit, and you’re heating it to 120 degrees Fahrenheit). Customer reviews state they’ve tested this model by running three showers at once and running multiple faucets or hot-water appliances with success. 

Cost: 4/5

This model costs around $1,915 directly from Rinnai on Amazon. This is in the average range for a whole-house tankless water heater, but is entering the high end of average. 

Energy Efficiency: 4/5

This model’s energy efficiency rate is 96%. This means it has a standby energy loss of less than 4%, which is outstanding for energy efficiency. The slight energy loss comes from the constantly burning pilot light. 

Lifespan: 4/5

While the warranty doesn’t go so far as to cover it for the full amount of time, averages indicate that this model will last anywhere from 12 to 15 years. This is an average lifespan for a gas tankless water heater. 

Warranty: 5/5

Rinnai offers a limited 12-year warranty on the heat exchanger, a 5-year warranty on components and parts, and a 1-year warranty (with an optional 5-year warranty) on labor costs. 

Limited 12-year on heat exchanger, 5-year on parts, 1-year on labor (5-year optional on labor). These are excellent warranty options. 


Rheem RTEX-18 18kW 240V Electric Tankless Water Heater, small, Gray

Rheem RTEX-18 Electric Tankless Water Heater

The best value for small homes requiring an electric whole-house water heater.

The Rheem RTEX-18 electric whole-house tankless water heater is a smaller option that has a few special features. There’s a digital thermostat control and LED display for ease of use. You can adjust the thermostat in 1-degree increments. Because this model is electric, you won’t need to have gas lines run or have ventilation installed. Here’s how this unit stacks up. 

Overall Score: 23/30

Performance: 4/5

This model has a Flow Rate of up to 6 gallons per minute (GPM). It operates at 18000 Watts, so it is a powerful electric model. Customer reviews rate the performance of this model at 4.5 out of 5 stars. 

Capacity: 5/5

The Flow Rate of up to 6 gallons per minute is above average for tankless models. This is enough to supply hot water for most usages, including dishwashers, showers, baths, faucets, and washing machines. 

Cost: 5/5

This model costs about $375, which is very low for a whole-house tankless water heater. Many other whole-house models are priced in the $1,000 range. 

Energy Efficiency: 5/5

Rheem advertises that this model has a 99.8% energy efficiency rate, which is very high. This indicates that it has an energy loss rate (lost heat) of less than 0.2%. 

Lifespan: 2/5

This electric tankless water heater has a shorter than average lifespan. The warranty coverage stops at the five-year mark, so it’s hard to imagine that it will last much longer than 6-8 years. However, the very low cost could still make it a cheaper option than a more expensive model that lasts twice as long. 

Warranty: 2/5

The Rheem RTEX-18 is backed by a 5-year heating chamber warranty and a 1-year parts warranty. These warranties are short compared to other options.


Stiebel Eltron Tankless Water Heater – Tempra 24 Plus – Electric, On Demand Hot Water, Eco, White

Stiebel Eltron Tempra 24 Electric Tankless Water Heater

Affordable electric tankless water heater with an average lifespan and performance.

The Stiebel Eltron Tempra 24 is an electric tankless water heater meant for smaller homes or low to regular hot water usage. Offering a Flow Rate of 4 gallons per minute, this water heater is best for single-point use or households with 1-3 people. With two, it’s enough for a larger household and multiple points of hot water usage at once. Here’s why it’s one of the best. 

Overall Score: 20/30

Performance: 3/5

With a 4 GPM Flow Rate, little electricity usage, and an average 4.6 out of 5-star reviews, this model has an average performance level. Keep in mind that it is a small unit for households with 1-3 people. 

Capacity: 3/5 

This model can produce about 4 gallons per minute (GPM) of hot water, which is enough for just about any type of hot water usage (shower, bath, dishwasher, washing machine, etc.), but not quite enough for multiple points of usage at one time. Because two units may be required for a household with four or more people or heavy hot water usage, we give this a 3/5 rating. 

Cost: 3/5

This model’s cost is about $580, which is below average for a whole-house tankless water heater but above average for a single point tankless water heater. Considering that this tank can do either, we give it a 3/5 rating on price.

Energy Efficiency: 5/5

This model has a 99% energy efficiency rating, which is outstanding. It is an electric model, so there is no energy loss from a burning pilot light. This unit has a standby energy loss of only 1%. 

Lifespan: 3/5

The available customer reviews state that this model lasts for an average amount of time, typically somewhere in the range of 10 to 12 years. Bear in mind that the warranty coverage won’t last quite as long. 

Warranty: 3/5

Stiebel Eltron provides two types of warranties on this model. There is a 7-year limited leakage warranty and a 3-year parts/components warranty included with purchase. 

Tankless Water Heater Buyer’s Guide

When it’s time to replace your water heater, considering a tankless water heater is smart. Tankless water heaters (aka  instantaneous demand-type water heaters) provide hot water to a household in a different manner than traditional tank-style models.

They are more energy-efficient, but their capacity is limited because of the way they operate. Tank water heaters hold and pre-heat large amounts of water in a tank, so it’s ready when a hot water tap is turned on. Tankless models heat only the amount of water being used when a hot water tap is turned on.

How It Works

Man standing in a shower with one of the best tankless water heaters heating the water above his head

When you turn on a hot water tap, cold water travels into the tankless water heater through a pipe. Depending on the model, a gas or electric burner will instantly heat the water to the right temperature. The heated water then comes out of the tap.

Since there’s no tank to limit the amount of hot water available, tankless water heaters are a constant source of hot water. But their design limits the flow rate of hot water more than tank-style models.

Because tankless water heaters don’t hold and heat large amounts of water, they are much more energy-efficient than tank-style models.

In this complete buyer’s guide, we’ll share everything you need to consider in your search for the best tankless water heater. We’ve also reviewed the tankless water heaters on the market to provide you with our picks of the five best tankless water heaters. Let’s get started.

Things to Consider

What are the most important things to consider when you’re shopping for a tankless water heater? At first glance, you may not see much difference between the different models, but a closer look will show you that some models are much better choices than others.

The performance capabilities, capacity, cost, energy efficiency, lifespan, and warranty coverage are important criteria to consider when looking at tankless water heaters. Here’s what to look for when shopping for a tankless water heater.


Tankless water heaters in big and small sizes against blue background

Tankless water heaters perform differently from their older tank-style counterparts. Knowing the average performance levels for this style of water heater will help you compare and choose the best tankless water heater for your needs.

We measure a water heater’s performance by the rate at which they provide hot water and BTUs the burner provides. Most tankless water heaters can provide anywhere from 2 to 8 gallons of hot water per minute.

Consider that the average 8-minute shower uses about 17 gallons of water, or about 2.12 gallons per minute. To ensure there’s always plenty of hot water, consider looking for a tankless model that provides at least 4 gallons of hot water per minute.

Look for a model that has a burner with enough BTUs to adequately provide hot water for your home. Most tankless water heater burners have 95,000 to 199,000 BTUs, so keep this range in mind as you shop.

Tankless Water Heater vs. Tank Water Heater Performance

Traditional water heater vs tankless water heater comparison as a featured image for the best tankless water heaters

Tank-style water heaters measure performance with the First-Hour Delivery rate in gallons per hour (GPH) instead. For example, a gas tank-style water heater might have an FHD rate of 100, meaning it can provide 100 gallons of hot water when the tank is full.

So using the same 8-minute, 17-gallon shower example from above, you could take nearly six showers back to back before exhausting the amount of hot water in the tank.

After that, the tank’s recovery rate – how quickly it can replace and heat the cold water that enters the tank – becomes an important factor. Less hot water is available once the tank is emptied because the unit has to constantly work to heat the incoming cold water for use.

This is the major limiting factor for tank-style water heaters and where tankless models excel. They are a continuous supply of hot water because the hot water never runs it. It’s instantly heated when a hot water tap is turned on.


Because tankless water heaters don’t have a tank to hold water, they don’t really have “capacity” in the physical sense. The amount of hot water they’re capable of providing on-demand is the same thing typically measured when a water heater tank’s capacity is considered.

There’s just no tank involved because the process is instant. Instead of their physical capacity to hold and pre-heat water, we look at a tankless water heater’s flow rate – their capacity to instantly heat water. How much water can they heat in a minute?

How many different hot-water appliances can they support at once? These are the important questions to consider when you’re looking at the different capacities of tankless water heaters.

Home appliance usage illustrated on a chart featuring water needs and flow per activity

Above, we mentioned that most tankless models can heat from 2 to 8 gallons of water per minute. Consider these common household hot water usage amounts:

– Bath: 27 gallons to fill
– Shower: 17 gallons
– Dishwasher: 15 gallons/load
– Faucet: 2.5 gallons
– Garden hose: 8 gallons
– Hot tub: 470 gallons to fill
– Lawn sprinkler systems: 3-10 gallons
– Pressure washer: 2-5 gallons
– Toilet: 2.5 gallons
– Washing machine: 34 gallons/load

Two to eight gallons per minute may not be enough to support heavy or multiple faucet usage in a large household, so most homeowners have come up with two different solutions:

1. Installing one or more additional tankless water heaters in parallel with each other to increase the amount of hot water available at a given time.
2. Installing single point tankless water heaters for appliances that are known for heavy hot water usage, like a washing machine or dishwasher.

Consider these options as you shop around for the best tankless water heater. Overall, tankless water heaters may have a reduced flow rate compared to tank-style models, but they constantly and consistently generate a steady flow of hot water. That makes their capacity superior to tank-style models. 


The cost of tankless models varies pretty widely, but it’s good to know the average price range for these units. Overall, you can expect to pay two or even three times more for a whole house tankless water heater than you would for a tank-style model.

Electric models are about $200 cheaper than gas models on average, but gas models are a little more efficient, so it’s a tradeoff.

Big vs small tankless water heater costs illustrated with a vector image

Single point tankless water heaters: Cost ~$150+; often electric; have less capacity and are intended to supply hot water at a single tap (like a bathroom shower, dishwasher, or washing machine)

Whole-house tankless water heaters: Cost ~$1,000+; gas or electric; have more capacity and can supply an entire house with hot water at multiple taps

In addition to the cost of purchasing a tankless water heater, you’ll also have the cost of installation. The process takes about 3 to 4 hours and should be handled by a professional.

Expect to pay anywhere from $150 to $600 for tankless water heater installation. If the installation also involves removing an old water heater or running new gas lines, that cost will rise by about $500.

Energy Efficiency

Tankless water heaters are often chosen because of their superior energy efficiency over tank-style models. Tankless water heaters may use up to 35% less energy than traditional storage water heaters and cost about $116 less to operate annually.

As a consumer, you may want to choose a tankless water heater that is considered energy efficient as one of your conditions of purchase. Because of the difference between storage and tankless models, the Department of Energy uses different criteria to rank tankless water heater’s energy efficiency and deliver the ENERGY STAR certification.

The Energy Factor and Uniform Energy Factor are two ways the DOE objectively measures and compares tankless water heaters’ energy efficiency to decide which get the certification.

To be ENERGY STAR certified, tankless water heaters must:

Have an Energy Factor (EF) greater than or equal to 0.90 OR a Uniform Energy Factor (UEF) rating of at least 0.87
Provide greater than or equal to 2.5 gallons per minute (GPM) over a 77-degree rise, but no more than 2.9 GPM over a 67-degree rise to be ENERGY STAR-UEF certified
Come with a minimum six-year warranty on the heat exchanger component and a 5-year warranty on other parts

When you shop for a tankless water heater, look for one that either has the ENERGY STAR certification or that has the highest EF/UEF you can find within your budget.


Another thing to be on the lookout for when shopping for a new tankless water heater is the estimated lifespan. Overall, tankless water heaters have a much longer lifespan than gas and electric tank-style water heaters.

Gas water heaters tend to last anywhere from 8 to 12 years. Electric water heaters may last from 8 to 15 years. But tankless water heaters typically last anywhere from 10 to 20 years.

Some of the lifespan-shortening features tank-style water heaters have aren’t a problem for tankless models. For example, tank-style models corrode over time, along with internal components (like the sacrificial anode rod) that may end up needing to be replaced.

The tank itself can corrode and rust, making the tank useless and requiring a complete replacement well before the ten or 12-year mark. Tankless water heaters don’t have these problems because they don’t store large amounts of water.

By the 20 year mark, a homeowner could go through two tank-style water heaters and spend more money than one who buys a tankless model covered by warranty through the twentieth year.

Be sure to take a look at the warranty policy for each tankless water heater you’re considering. The warranty length and coverage can be a clue as to how long the manufacturer believes the appliance will last.


The available warranty is the final factor you should consider when shopping for a tankless water heater. Most tankless water heater manufacturers offer a warranty that varies from as little as six years up to about 15 years.

The longer the warranty, the better the product – or the more the manufacturer stands behind it. Tankless water heater warranties don’t always cover the same things. Some warranties may cover the unit itself as a whole.

Some may cover only the internal parts and components. Some cover complete replacements. Looking for the longest warranty that offers the best coverage will ensure you end up with a reliable unit that the manufacturer fully backs for a decade or more.

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