Tankless Gas Water Heaters Reviewed

37 Products Evaluated
57 Hours of Research
2 Experts Interviewed
237 Reviews Analyzed

Author: Matt Wilson | Editor: Esther Lindenberg | Fact-checking: Rex Cauldwell

Last Updated: October 7, 2021

New house constructions are adapting to on-demand water heaters so that homeowners could choose whether to install the heater during construction or later. It’s becoming more of a necessity due to the new regulations that recommend these energy-efficient types of water heaters.

 ProductGPMApprox. UsageRating & Price
Rinnai RUC98iN Natural Gas Tankless Water HeaterCheck price on HomeDepot
  • UEF (Efficiency Rating): 0.93
  • Energy Star® certified
  • Two venting options (Concentric or PVC)
  • Very easy to maintain (with wifi alerts)
  • Best value for the price
  • Great customer service
9.8Check price on HomeDepot
Rinnai RUR199iN Tankless Water HeaterCheck price on HomeDepotCheck price on Lowe's
  • UEF (Efficiency Rating): 0.93
  • BUILT-IN recirculation pump with a timer works even without a dedicated return line
  • Energy Star® certified
  • It sustains high GPM flow rate for low temp income water
  • Highest GPM (with prarmeter adjustment)
  • Multiple venting options
  • Wi-Fi ready (with additional module)
11Check price on HomeDepotCheck price on Lowe's
Noritz NRC66DVNG Indoor Tankless Water HeaterCheck price on HomeDepotCheck price on Lowe's
  • UEF (Efficiency Rating): 0.91
  • vents with Schedule 40 PVC
  • Low NOx emissions
6.6Check price on HomeDepotCheck price on Lowe's
Rinnai V65i-N Natural Gas Tankless Water HeaterCheck price on HomeDepotCheck price on Lowe's
  • UEF (Efficiency Rating): 0.8
  • Many sizing options
  • Can easily replace 50 gallon tank
  • Great choice for mobile homes
  • Control-R 2.0 mobile app allows you to set timers and schedule the water heater remotely
6.6Check price on HomeDepotCheck price on Lowe's
Eccotemp i12-NG Tankless Water HeaterCheck price on HomeDepotCheck price on Lowe's
  • UEF (Efficiency Rating): 0.79
  • Sleek, modern design with LED display control panel
  • It has energy saving mode which makes it even more efficient
  • Clear installation instructions

*do not buy this unit if you live in places where the temperature drops below freezing. It may not be able to keep up

4.8Check price on HomeDepotCheck price on Lowe's

The Ultimate List of the Most Reliable and Efficient Tankless Gas Water Heaters

Here is the list of the best tankless gas water heaters to buy in 2021:

1. 🥇 Rinnai RUC98IN Ultra Series

Rinnai RUC98iN Ultra Series Tankless Gas Water Heater Specs:
  • UEF (Efficiency Rating): 0.93
  • Product dimensions: 10 x 18.5 x 26 inches
  • Flow rate: 9.8 GPM
  • Concentric or PVC venting option
  • Energy Star® certified

From afar, the Rinnai RUC98IN looks somewhat bulky, but it makes up for bulkiness by being efficient and powerful. Its size makes it perfect for both commercial and residential uses. It stands tall at 26 inches by 10 inches and weighs about 61.7 pounds.

Rinnai RUC98IN has a sleek body that comprises of a gray exterior. It also has a control panel with a digital display, power button, gas, and water buttons. There is also a feature that allows you to lock the temperature button; this will prevent unauthorized access.

Energy Efficiency. The Rinnai RUC98IN is arguably the most energy-efficient water heater in its class. It boasts of an energy factor of 0.95. It means that for every 1 dollar you spend on the energy you get 95 cents worth of hot water.

The Rinnai’s gas burn rate ranges from as low as 15,200 to as high as 199,000 Btu. The residential model is good enough for heating water for home use as it can reach up to 140 degrees Fahrenheit while the commercial model can reach up to 185° Fahrenheit. 

It’s also Energy Star certified, so you might get a rebate from your local utility for using this.

Capacity and sizing. Due to the increasing price of real estate, homeowners are becoming more conscious about how they use their spaces. For this reason, you don’t want an oversized heater that will be just as effective as a smaller water heater. Fortunately, the Rinnai RUC98IN has a sleek and compact body that allows for easy installation and occupies less space. 

Its manageable size allows you to install it close to where you need the hot water. This reduces energy loss by facilitating faster delivery and increasing efficiency. Also, the water heater has a high volume output of 9.8 gallons per minute. With such a high output, you can have four or five water outlets running simultaneously. 

Things we liked:

  • There is a reduced risk of water contamination due to the absence of a storage tank
  • Comes with two venting options 
  • High flow rate allows you to use multiple faucets or talking two to four showers simultaneously
  • Compact sizes
  • Fairly easy installation

Things we didn’t like:

  • It’s quite expensive 
  • When serving too many water outlets the water pressure or the temperature may drop

2. Takagi T-H3-DV-N

Takagi T-H3-DV-N Condensing Natural Gas Indoor Tankless Gas Water Heater Specs:
  • UEF (Efficiency Rating): 0.93
  • Product dimensions: 11.2 x 17.8 x 24.9 inches
  • Flow rate: 10 GPM
  • Sound level: 55 dB
  • Energy Star® certified

The Takagi T-H3 has a compact design, but its efficiency is one of its kind. It’s the best tankless gas water heater for homes that require a continuous on-demand supply of hot water. It has a flow rate of 10 GPM and a maximum gas burn rate of 199,000 Btu. As such, the Takagi T-H3-DV is ideal for larger homes that have up to 5 bathrooms. Its application ranges from residential to commercial as it’s also suitable for restaurants, recirculation systems, etc. 

Energy efficiency. Since the Takagi T-H3-DV-N is a condensing unit, it uses secondary heat exchangers that are made of a copper alloy. This material has better corrosion resistance than conventional materials. It’s also more durable and resistant to thermal and mechanical damage, which often occurs when heating water at high temperatures.

The indoor model has an energy factor that is lower than that of the outdoor model. Its energy factor stands at 0.93, while that of the outdoor model is 0.95. However, the indoor model is better because it is less noisy.

Size and longevity. The Takagi T-H3-DV-N measures 11.2 inches by 17.8 inches by 24.9 inches. Due to its compact size, installation becomes even easier. It weighs 60 pounds, thus needs to be installed in an area where it doesn’t have to be carried around. 

Being a product of a Japanese company and A.O. Smith, Takagi features the best water heating technology that both Japan and America has to offer.

Besides, it has a 15-year limited warranty, but it only applies to residential use heaters. Commercial-use water heaters get a 10-year limited warranty.

 Advanced features. It comes with multiple control features such as the built-in temperature controller. It also has an error display, water flow display, pushbuttons, and status indicator.

Also, the water heater has surge protection, self-modulating heat mechanism, and anti-freeze. Cumulatively all these features will help improve energy efficiency, thus reducing your water bill.

Things we like:

  • Ideal for large families 
  • Super quiet 
  • Low NO2 emission levels 
  • Durable and can for up to 20 years 

Things we didn’t like:

  • Complicated installation 
  • Requires proper venting 
  • Doesn’t provide instant hot water
  • High activation flow rates

3. Noritz NRC66DVNG

Noritz NRC66DVNG Indoor Water Heater Features and Specs:
  • UEF (Efficiency Rating): 0.89
  • Product dimensions: 6.7 x 13.8 x 23.6 inches
  • Flow rate: 6.6 GPM
  • Can be vented with Schedule 40 PVC Pipe and Fitting
  • Energy Star® certified

The Noritz NRC66DVNG features a simple design that is incredibly powerful. The Noritz NRC66DVNG is smaller and lighter compared to the other heaters on this list. It weighs only 39 pounds. 

Energy Efficiency. The Noritz NRC66DVNG is a condensing unit; thus, it gives out extreme heat while maintaining high efficiency. Its energy consumption is average as it consumes 54 watts when heating water, but it rises to 138 watts when operating on the antifrost mode.  It’s arguably the best tankless gas water heater for cold climates. 

You can connect it to a battery backup when there’s a power outage. Its energy factor stands at 0.91, which is decent, considering that it’s a gas-powered water heater. Its nitrogen oxide emissions are pretty low but not low enough as required by the industry standards.

Materials. The Noritz NRC66DVNG has an impressive build that comprises of commercial-grade K Copper, which is said to be 25% thicker than any other type of copper.

It also has a steel casting that is combined with polyester coasting to improve its durability. To further enhance its durability, the manufacturer added safety features such as fan rotation detector, flame sensor, freeze protection, temperature control lock, and condensate overfill detector as well as an overheating protection device.

The heater is also covered with a 12-year limited warranty. 

Output. The Noritz NRC66DVNG gas consumption needs range from 15,000 – 120,000 Btu per hour. Such a burn rate can only deliver 0.5 GPM as the minimum hot water flow rate and 6.6 GPM as the maximum flow rate. 

Things we like:

  • High efficiency
  • Ideal for smaller families and/or homes in colder climates
  • A digital temperature control system 

Things we didn’t like:

  • Not suitable for larger homes
  • Quite noisy 

4. Rinnai V65iN

Rinnai v65iN tankless gas water heater
Rinnai v65iN tankless gas water heater;
Rinnai V65i-N Indoor Tankless Gas Water Heater Features and Specifications:
  • UEF (Efficiency Rating): 0.8
  • Product dimensions: 13.9 x 8.8 x 23.6 inches
  • Flow rate: 6.5 GPM
  • Activation Flow Rate: 0.26 GPM
  • Energy Star® certified

Rinnai has been in the water heating industry for almost a century. Over the years, they have improved their technology and water heaters to ensure that homeowners get a continuous supply of hot water when the need arises. 

This innovation means that the Rinnai V65i-N will operate only when needed. Rinnai V65i-N uses 40 percent less energy compared to traditional heating systems, which translates to reduced utility bills.

Wi-Fi technology. The application of Wi-Fi connectivity to almost every home appliance is making life more comfortable. For instance, the Rinnai V65i-N has Wi-Fi connectivity, which allows you to monitor the water heater remotely via your smartphone. You get access to vast management options that give you more control over this tankless gas water heater.  

Size. The Rinnai V65i-N is small as it almost the same size as a small suitcase. Its small compact design comes in handy during installation as it saves space. You can mount it on an exterior or interior wall. 

You can also install it in non-conventional spaces such as the attic, thus freeing up space, especially in small homes.

Energy efficiency. The Rinnai V65i-N features energy-efficient technology. Its copper heater exchangers function at maximum efficiency, which reduces energy consumption by close to 40 %. In addition to being a tankless water heater, the Rinnai V65 also uses electronic ignition.

Also, the V65i-N comes with an option that allows you to customize your efficiency. Its energy consumption while in standby mode is 2 watts, 76 watts on normal mode, and 120 watts while on antifrost protection mode.

Great Performance. The value series offers the perfect blend of comfort and value. Its maximum flow rate is 6.6 GPM, while its maximum gas consumption is 150,000 Btu. The flow rate can only sustain two bathrooms; thus, the heater is suited for smaller homes. The Rinnai V65i-N boasts of a 0.82 energy factor, which is higher than that of storage tank heaters.

Things we liked:

  • App integration allows users to control the heater remotely 
  • Ideal for smaller homes and apartments 
  • Comes with a leak detection system 
  • Small size saves on space 

Things we didn’t like:

  • Doesn’t come with a venting kit 
  • A bit slow to heat up 
  • Quite noisy 

5. Eccotemp i12-NG

Eccotemp i12-NG Tankless Water Heater Specifications:
  • UEF (Efficiency Rating): 0.8
  • Product dimensions: 16 x 16 x 11 inches
  • Flow rate: 3 GPM
  • Activation Flow Rate: 0.26 GPM
  • 80,000 BTU Heat Output

As technology continues to improve, tankless water heaters have not been left out in this technological revolution. The Eccotemp i12-NG water heater features a blend of new technology and stylish design. It’s an indoor model with a futuristic design that comprises of a black acrylic glass casing. 

Maximum Flow rate. The Eccotemp i12-NG may not be as powerful as other models on this list, but it’s pretty good for its price. It has a flow rate of 4.8 GPM, which is lower, compared to some water heaters that can reach 10 GPM. While it’s not suitable for commercial use, it’s good enough for small residences.

The unit can sustain one bathroom and regular household chores, but it will struggle in a bigger house with several bathrooms

Advanced technology. The Eccotemp i12-NG is a state-of-the-art indoor water heater that comes with user-friendly technology. It has fully automated controls, an LED display, and an electronic ignition system. The addition of new technology, such as the LED display makes it easier to interact with the system.  

 Size. Understanding the size of a water heater comes in handy during installation, as the size will determine where best to install it. The Eccotemp i12-NG is small as it measures 16 x 16 x 11 inches. Its small size means that you can install it almost anywhere you want.

Things we like: 

  • It’s made of stainless steel which is durable and allows for long term use 
  • Automatic temperature control improves the precision
  • User-friendly design and technology
  • Stylish design 
  • Max flow rate is sufficient for smaller families

Things we didn’t like:

  • The small size means that it’s only good enough for small-sized families
  • Doesn’t function well at high elevation 
  • Cost of installation is high due to the installation of large venting pipes 

Natural Gas Tankless Water Heater Buyer’s Guide 

Thinking of replacing your water heater? Maybe you are looking to install a water heater in your new home, but you’re not sure what to choose. Don’t worry; this guide will come in handy.


Size matters a lot, especially considering the size of your household. How many members does your family have? How big is your house, and how many bathrooms do you have?

You see, a smaller house with two bathrooms will require a water heater that is powerful enough specifically for that particular home. Alternatively, larger homes require the best tankless water heater for large homes.

Choosing the right size will provide you and your family with a continuous hot water supply. Before making the decision, calculate the first-hour rating of the household. The first-hour rating refers to the amount of hot water consumed during the busiest hours. Typically the most active hour for hot water consumption is in the morning.

Now select a water heater that will deliver the required amount of water when it’s most needed. Use our sizing guide for reference. 


Although it’s often overlooked, space is a critical factor that will influence your choice. For instance, if your house doesn’t have sufficient space to store a large water heater, you will have to opt for a smaller and more compact water heater.  

This is why tankless water heaters are more convenient as they require less space. In addition to being smaller, tankless water heaters are more flexible and easy to mount on walls. 


Energy efficiency is becoming a major part of our decisions, as more consumers are now trying to go green and save energy.

More efficient units will also save you more money because they waste much less energy than a typical tank water heater. You’d want to look at the energy factor (UEF – Uniform Energy Factor). The higher it is – the better. For example, the Rinnai Ultra Series have 0.93 UEF. It means, that for every dollar you spend on energy, you get 93 cents worth of hot water, which is not bad at all.


Tank leakage is a common problem for storage water heaters. Tankless units don’t have this problem, because they don’t have a tank. But sometimes they do suffer from bad maintenance and calcium build up. Especially if you use hard water from well without water softeners.

Tankless gas water heaters require annual descaling. It’s a very easy process and you can do it all by yourself with basic tools, descaling solutions (basically, a lot of vinegar) and a couple of Youtube videos.

Also if something breaks, the warranty will cover the repair.

Fuel Type 

The fuel type will affect not only the energy efficiency and size of your unit but also the annual operating cost. Common fuel choices include natural gas, electricity, and propane. This choice will also be influenced by the type of fuel available in your area.

Tankless gas water heaters tend to be more expensive than their electric counterparts. They are also more costly to maintain. They are the best option when your house is connected to a natural gas line.

Alternatively, electric water heaters are cheaper, but the cost of installation will skyrocket when you need to upgrade the entire electrical system. Electric water heaters have a simplistic, user-friendly design that is easy to diagnose and repair. They are also more energy-efficient than gas tankless water heaters.


Be sure to check the warranty before you complete that purchase. Does the water heater come with a warranty? If yes, what did the warranty cover, and for how long is it viable? You need a warranty that covers you in case the heater breaks down or malfunctions. Read through the warranty and understand what is covered and what isn’t.

Benefits of using a tankless gas water heater 

Before we get into the natural gas tankless water heater reviews, let’s take a look at the benefits.

It saves energy and money

As the name implies, tankless water heaters do not require a tank. Therefore, they are more energy-efficient as they don’t expend energy trying to keep the tank hot. The heater does not consume power when on standby and uses it only when hot water is needed. Once you install one of these, you will notice that your energy bill will reduce by up to 40%. 

It lasts longer

Also, since there is no tank to store the water, it doesn’t run a risk of corrosion due to magnesium and calcium. Nevertheless, it’s advisable to use a water softener and flush the system once a year.

Lower risk of corrosion translates to longevity. Typically, a tankless water heater can last up to 30+ years if it’s well maintained.

It saves space

With a traditional water heater, you have to figure out where to install the tank. However, your storage options increase with a tankless water heater since the heaters are compact. Even the best tankless gas water heaters for large homes are still compact.


Several factors will influence your decision on the best tankless gas water heater. Some of these factors have been discussed in the buyer’s guide, but the final decision yours. What exactly are you searching for? Take your time to analyze the products available vs. your needs. And most importantly, check the fuel type. Does the water heater run on electricity, natural gas, or propane?

Which of these fuel sources is available in your locality? What is the cost of maintaining the water heater? How will the water heater affect your energy bill? If you’re hoping to lower your energy bill, choose a heater that has a high energy factor like the Takagi T-H3-DV-N Indoor Tankless Water Heater. It has an energy factor of 0.93 and a flow rate that can sustain up to 5 bathrooms simultaneously. This makes it perfect for larger homes, unlike the Eccotempi i12-NG, which has a flow rate of 4.8 GPM.