5 Best Gas Tankless Water Heater Reviews & Comparison Chart

The best tankless gas water heater is one of the most frequently used heating machine, as it is powered by natural gas, the using costs are relatively low.

There are many types of best tankless gas water heaters on the market, indoor type, outdoor type, whole home type, and also portable type. On choosing a tankless gas water heater, you should take the actual needs of yours into consideration.

Here we would give you some suggestions on how to choose, and listed several top-rated tankless gas water heaters for you.

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Top 5 Tankless Gas Water Heater of 2021

What Is Tankless Gas Water Heater?

The tankless gas water heater is a heating machine, powered mainly by natural gas. It heats water in a few minutes or even in a few seconds, able to support consistently hot water for you. Unlike a tank water heater, it saves far more space for your home, and you do not need to worry about running out of money when taking a bath. However, as carbon dioxide needs to be emitted in use, ventilation needs to be installed especially for indoor types.

Why Tankless Gas Water Heater?

1. It is more environmentally friendly.

Compared with other petroleum-based fuels, the tankless gas water heater is much cleaner; it emits 45% less carbon than other non-gas tankless water heaters.

2. It is more efficient

Compared with other nongas tankless water heaters such as electric types, the gas water heater is 3 times more efficient, and there are nearly up to 90% usable energy in use. The usable energy of other types reaches around 80% or even less.

3. It is more economical

The whole using costs of tankless gas water heater are relatively low but are more powerful. According to a professional test, a gas-powered tankless hot water heater is able to save 30% less money for you on heating bills each month.

4. It is more reliable

For gas tankless instant hot water heater, natural gas is transferred and used through underground pipelines; you can use it in multiple applications at the same time. Thus it is more reliable and safe.

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Different Types

With different installation spots and applications, tankless gas water system types are various; they can be divided into an indoor type, outdoor type and whole-home type, portable type. Here we will give a fundamental difference and features of each type. And for each model, we have done detailed reviews for you; you can choose directly the most suitable one based on your needs.

<Installation spots>

1. Indoor gas tankless water heater

Indoor gas tankless water heater refers to the heating machine that installed indoor, whether in the bathroom or kitchen or directly under water sink. The key to the indoor heater is the ventilation; venting kits must be installed along with a machine for gas to let out.

If installed it on point of use, then it takes only a few seconds for hot water flowing, primarily reduced the waiting time and saved much money for you. If you have an interest in such an item, just check our reviews made for you freely.

2. Outdoor gas tankless water heater

Outdoor gas tankless water heater, as the name suggests, is installed outdoor. But to reduce waiting time, it is often installed outside the wall of the bathroom or kitchen. No ventilation is needed. But you need to make sure it is well protected under severe weather and do not put anything flammable on the machine.

There are still many other things need to be considered on an outdoor gas tankless water heater, we have made reviews and pick several best outdoor gas tankless water heaters for you if you would like to know more.


1. Whole-home tankless gas water heater

When taking a bath, doing laundry, and washing hands at home, hot water is needed all the time. Thus you need to get a whole-house gas heater to support hot water for both shower and faucets. The flow rate of the whole house gas-powered type is relatively large and is much more powerful. You can get more information from the whole house tankless system reviews we made for you and choose the most suitable one.

2. Portable tankless gas water heater

A portable tankless water system, or the small tankless heater, refers to the machine that is small and light-weighted. It can be carried and used outdoor in camping or installed on RV. The flow rate of it is quite small, meeting the basic needs of hot water use. And of course, portable tankless gas water machine price is low. If you intend to get the best portable tankless water heater, please feel free to check on Amazon or read the reviews of us.

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Best Tankless Gas Water Heaters on The Market

1. Rinnai RUC98iN Ultra Natural Gas Tankless Water Heater

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This Rinnai natural gas tankless water heater is the star product and the hot-selling type in 2018. It needs to be installed indoor, and twin-pipe installation gives you more options and choices.


  • 9.8 GPM flow rate

This unit has a high flow rate reaching 9.8 gallons per minute. It can support three to four bathrooms and multiple kitchen faucets at the same time. It can also be used for commercial use when you cascade several of them together.

  • High-temperature range

The temperature range of the unit is between 98 degrees F to 140 degrees F, meets the needs of essential home hot water use. For commercial use, a commercial remote can raise the temperature to 185 degrees F., But you need to buy the remote separately.

  • High energy efficient

The power requirement of it ranges from 15200 to 199000 BTU per hour, and the efficient rating reaches up to 0.95, which means seldom energy is wasted in using period. The high energy efficient heating machine is able to save a large number of heating costs for you per month.


  1. 2 venting options offered (concentric PVC and twin pipe)
  2. Needs only 2 watts to keep the machine up and to run
  3. Takes up 20 seconds for hot water flowing
  4. 5-year warranty of the part
  5. Super quiet working condition
  6. Constantly hot water supply
  7. Commercial use available


Difficult to install, you need to get professional for help

2. Rheem RTG-95XLN Low NOx Outdoor Tankless Natural Gas Water Heater

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best gas tankless water heaters




This unit is an outdoor tankless gas water heater, so no venting kits need to be installed. Both natural gas and propane are available as a power source.


  • 9.5 large flow rate

The same as Rinnai tankless water heater we recommended above, the flow rate of the unit is also 9.5 gallons per minute, which means it can be served as a whole-house gas heater for a large family and for commercial quickly. Multiple bathrooms and faucets can be used at the same time.

  • High energy rating

The energy rating of the unit reaches up to 94%, which is really a high energy-efficient tankless water heater. Less carbon dioxide emitted in the using process, and it proves to environmentally friendly type.

  • Remote control available

EcoNet smart home technology of the machine enables you to control it remotely via an app, as an outdoor machine, you can simply adjust the gas power and water temperature at home with your phone.


  1. Stainless steel heat exchanger gives your option to connect both vents as water demand turns high
  2. Both propane and natural gas available
  3. Standard 10-year warranty on heating parts
  4. No ventilation requires for outdoor installation
  5. Remote control available
  6. Supports multiple bathrooms and faucets the same time
  7. Endless hot water supply


Need to be installed by professional

3. Takagi T-KJr2-OS-NG Outdoor Natural Gas Tankless Water Heater

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the best tankless water heaters gas




Takagi natural gas hot water tankless water heater has a lower flow rate than other brands of the heater, which is suitable for small or middle size home use.


  • 6.6 gallons per minute of water flow

The above two tankless water heaters we recommended are large flow rate types, reaching near 9.5 gallons per minute, while the flow rate of this unit is only 6.6 gallons. But it is still able to support one bathroom and one kitchen faucet the same time.

  • Stylish compact design

T-KJ2 series is proved to be the lightest and smallest in the whole lines of Takagi tankless water heaters. Able to save large space for you no matter for outdoor or for indoor installation.

  • 150 degrees F temperature

This unit provides hot water with a temperature above 150 degrees F; the demanded power input is 140000 BTU per hour, 0.83 energy efficient is also saving much money for your heating costs.


  1. Compact shape
  2. Propane and natural gas available both
  3. Constant hot water supply
  4. Easy to be installed
  5. Able to support two bathrooms simultaneously
  6. Demand minimal maintenance


The working noise is a bit loud

4. Naiven NPE-240-A Tankless Gas Water Heater

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best buy a gas tankless water heater




Naiven NPE-A series is excellent in its patented high technology inserted; it represents the tankless water heater of the future.


  • Buffer tank and recirculation pump built-in

This unit is designed with ComforFlow technology, it has a built-in buffer tank and recirculation pump, to reduce cold water sandwich and save water bills by reducing time to get hot water. It boasts that you need only one second for hot water.

  • External interface installed

The external interface is equipped to show water temperature and error codes, you can turn the button on and off quickly to adjust.

  • Condensing stainless steel heat exchanger

It is designed with patented condensing technology; dual stainless steel heat exchangers recover extra heat to reduce energy consumption and carbon dioxide emissions. It keeps the exhausted temperature low.


  1. Clear installation and using instructions
  2. Short waiting time for the hot water
  3. Pretty powerful
  4. Intelligent preheating technology makes live more convenience
  5. Good at keeping the temperature
  6. Quickly correct water temperature if it draws stops suddenly


  1. Slight working noise
  2. You need to buy extra remote for remote control

5. Noritz NRC661-DV-NG Tankless Hot Water Heater

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best tankless water heater for gas




This unit of Noritz is also a relatively small flow rate tankless hot water heater, reaching only 6.5 gallons per minute.


  • 6.5 gallons of water flow

Compared with other recommended gas tankless water heater, this flow rate is a bit low, but it is still able to meet the demand of two bathrooms use simultaneously. When used in cold areas or cold weather, one bathroom and faucet can be used at the same time also.

  • 2 heat exchangers

There are two heat exchangers made by different materials that can be chosen, one is stainless, while the other is copper, both of them last long and are corrosion resistance. There are also freeze protection devices installed inside.

  • High energy efficient

The gas consumption runs between 15000 and 120000 BTU per hour, and the thermal efficiency rating reaches as high as 93%, which helps save a large amount of money for you.


  1. Compact shape design
  2. Quiet working condition
  3. Can be vented with Schedule 40 PVC Pipe and Fitting
  4. Low NOx design
  5. Can be controlled remotely
  6. Freeze protection


Coldwater sandwich

Best Natural Gas Condensing Tankless Water Heater

Because of the individual working principle of natural gas tankless hot water heater, many of the leading brands make their heaters into condensing types, to reduce energy consumption and greenhouse gas.

There is some best natural gas condensing tankless water heaters we would like to suggest to you:

1. Naiven NPE-240-A Tankless Gas Water Heater

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best buy a gas tankless water heater

Each of Naiven tankless water heaters is equipped with condensing technology, it helps to reduce energy consumption and carbon dioxide emissions by recovering the extra heat that would be lost in non-condensing water heaters.

There are also many other Naiven natural gas condensing tankless water heaters you can choose, each of them is technically designed.

2. Noritz NRC661-DV-NG Tankless Hot Water Heater

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best tankless water heater for gas

This is also a condensing gas tankless water heater worth recommending. And it has two heat exchangers; one is made of stainless steel while the other made of copper. Together with its low NOx design, it is capable of saving much energy for you and heating costs.

What Should You Know About Gas Tankless Water Heaters

When buying gas tankless water heaters, you need to ensure that you know the available types. Continue reading our guide to know some of the best and common types of gas tankless water heaters.


The non-condensing gas water heaters are mostly used because they heat water using a heat exchanger. With the heat exchanger’s help, it can reach an efficiency factor of up to 0.85. In other words, as a buyer, you need to note that this is a well-proven technology that has been used in most developed countries such as Europe and Japan.

One of the main reasons why most people prefer non-condensing units is the fact that they are reliable and they also have few to no manufacturing problems. Note that they can come with few drawbacks such as they get quite hot and they exhaust quickly.

Condensing Hybrid

Another type of gas tankless water heaters that you need to know is the Condensing Hybrid. They incorporate a small water storage container that can carry up to 2 gallons. It is essential to understand that this tank keeps a reservoir of hot water, which helps to remove most of the shortcomings of this device.

Based on various researches that have been conducted, it has been found out that these condensing hybrid units operate at 94% efficiency. Once you find these types, note that they can be quickly vented using the PVC. That is why they are cost-efficient.


The condensing units are also referred to as the second generation of tankless water heaters. They usually use a secondary heat exchanger tool after their standard one. One of the main reasons you can consider using these tankless water heaters is that they can be vented using the PVC.

Electric vs. Gas Water Heater

Electric and gas are the two main power sources of tankless water heaters, many people may get trouble in which type should be chosen. Here we made a comparison between the two types of tankless hot water heaters:

Electric Tankless Water Heater:


  1. Do not directly emit carbon dioxide
  2. More affordable
  3. Do not need ventilation
  4. Do not affect by high altitude


  1. Less powerful, requires multiple units to support equal power as gas type do
  2. Require more maintenance in using
  3. More expensive on using costs and heating bills.

Gas Tankless Water Heater:


  1. More powerful, able to support multiple faucets and bathrooms the same time
  2. Lower cost than electricity
  3. Able to heat water in a cold climate
  4. Safer in using


  1. More expensive on price than electric
  2. Emit carbon dioxide directly from the vent
  3. Needs ventilation

The Most Important Gas Tankless Water Heaters Features and Specification

There is no doubt that tankless water heaters can help you save time and money in the long run. However, if you are planning to purchase it, note that this is not the only benefit that you will get. For beginners, if you manage to buy the best tankless water heaters, you will save more, primarily once you use it economically.

When you are planning to purchase a gas tankless water heater, know the there are some of the specifications or features that you need to know. Ensure that you can find the right heater with the best elements that you want. After all, the best gas tankless heater is the one with more features and specifications.

Best Gas Tankless Water Heater Features and Specifications

  • Required certifications
  • High power input
  • Cold safety
  • Warranty on heat labor, parts and exchanger
  • Non-condensing and condensing features
  • Proper venting systems
  • Suitable water flow properties

The above features or components can either break or make your future purchase. Before you decide to purchase it, ensure that you take your time to correctly choose a gas water heater that will suit your needs.

Top 3 Best Tankless Gas Water Heaters

Buying Guides on Choosing Best Gas Water Heater

Facing so many brands and various types of tankless gas heaters, you must get trouble on which one is the best and which brands should I choose. There are a few factors that you need to take into consideration before selecting:

1. Flow rate

Different flow rate points to different user applications. Small flow rate types such as 2-3 gallons per minute tankless water heaters are normally portable or point of use types. They can be a good helper outdoor in traveling or camping, but for whole house using, the small rate is not capable enough to support enough hot water for you. So before selecting, you need to make sure the exact flow rate you need.

2. Ventilation

As natural gas serves as a major power, the gas tankless water heater needs ventilation kits to emit used gas out. The universal ventilation kits are sometimes not suitable for each machine; some of the heaters require special ventilation. And needed PVC pipes are also different, knowing clearly about the ventilation method can help save a large amount of money for you.

3. Size

The size of the gas heater has something to do with the size of your home. If you have a large home and intend to use it for the whole home, then we would like to suggest the whole house tankless water heaters for you. However, if you lack space and just want something small to support faucet use only, then you can choose the under sink tankless water heater.

4. Energy efficient

An energy-efficient tankless water heater can save a large amount of money on using costs and especially on heating bills. For a gas tankless water heater, thermal efficiency is an essential consideration for you, some of which reach up to 95%, which is highly efficient types, while some reach only 60-70%.

5. Waiting time

The waiting time of the water heater refers to the time for hot water flowing out of the pipe to the destination. The longer the waiting time is, the more cold water wasted, and thus water bills will be added accordingly. Therefore choosing a fast waiting time machine can save money for you to some extent.

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best rated natural gas tankless water heater


  1. For indoor installation, venting kits must be installed
  2. Do not put any inflammable things on the heating machine
  3. The heater should be installed at a safe distance with water or other devices.
  4. Stop using it once something wrong happens
  5. Remember to turn off the gas valve every time you stop using it
  6. Always use it under instructions required

Gas Water Heater Prices

One feature of the tankless gas water system is its high purchasing price, most of which are around $1000, and of course, there are also installation costs as well as venting costs if installed indoor. But it totally worth the price, for the using costs, can be extremely low and hardly need maintenance in later use.

It is proved that tankless gas water machine is able to save 30% money on heating and water bills each month, and the service life of it reaches as long as 20 years for some brilliant types. For long term use, a tankless gas water system is basically equal with an electric tankless water heater type or even cheaper.

But still, you need to select reasonably according to your actual needs and budget; there are also many other excellent tankless gas water system with relatively low price, if you have an interest, please feel free to check it on Amazon. Constantly discount on Amazon will save a large amount of money for you.

How to Size a Gas Tankless Water Heater?

As a buyer, you need to understand that the size of any water heater that you are willing to purchase should not be taken lightly. Once you find the right unit, you will be in the correct position to ensure maximum efficiency. For you to size a gas tankless water heater, the following are some of the things you need to consider.

Temperature Rise

When planning to size a gas tankless water heater, you have to consider the current temperature and the recommended output level. They are among the crucial things that will help you to have the correct measurements. However, one of the things you need to note here is that the standard water temperature should be around 50F.

The Flow Rate

The next essential thing that you need to consider is the flow rate. You need to take all showerheads, kitchen, and bathroom faucets into account to determine the right size of the water heater. Depending on the number of devices that the heater will cover, make sure that you find an appropriate unit that will cover all the tools in your home. For instance, you need to know that tubs and showers spend around 2 to 4 gallons each minute. On the other hand, the average faucet consumes over 0.75 gallons per minute. Therefore, know your needs before going for these appliances.

The Pros and Cons of Gas Tankless Water Heaters

Ideally, every product that you purchase comes with both the cons and the pros. Once you decide that you need a specific product, ensure that you determine if its benefits are worth it for you to continue with your purchase. Below are the advantages and disadvantages of tankless water heaters.


Energy Efficiency

As mentioned earlier in our post, gas units can reach up to 96% energy efficiency. Due to this reason, they are among the most efficient water heaters that you can find on the market today.

Ideal for Smaller Homes

Most homeowners found it hard to purchase the right tank units due to limited space. However, tankless heaters come with low GPM models that are ideal for small homes. If you are limited to area, this is the right tankless heater that you need.

Environmentally Friendly

Even if most of these tankless water heaters run on gas, it is crucial to note that they have a reduced environmental impact. In other words, this means that they need less energy to operate, and they produce fewer greenhouse gases.

Enhanced Lifespan

Even if most of the tank units can last up to ten years, it is vital to note tankless water heaters can offer you with hot water for even twenty years when services correctly. Regardless of them being more expensive, these units can save a lot of time and money.

Can be Placed Anywhere

It is crucial to note that tankless units are smaller than the tank units. In other words, this means that they can be placed virtually anywhere.


Extra Equipment

Based on the water you are supplied with, the chances are that you may need a softener that can help you to reduce water hardness. It is essential to note that a water softener will not only enhance your overall costs but also end up taking more space than the heater itself.

Fluctuations in Temperature

Tankless water heaters need to continuously heat water, which is why they are subjected to temperature fluctuations. In most incidents, this problem always comes up when you use different faucets.

They are Expensive

It would help if you understood that traditional heaters cost up to $500. Also, it is crucial to know that a tankless unit can end up costing up to $1 000 or more. Apart from that, it is critical to note that they need a professional to install them.

Extensive Retrofitting

If you are planning on using these tools, you need to retrofit the gas and venting system of your home for you to use them. On the same note, keep in mind that most of these gas units are not compatible with the venting and piping in most homes.

The Costs Involved By Gas Tankless Water Heaters

When you want to install a gas tankless water heater, ensure that you set a budget over $3500. As mentioned above, most of the gas models need venting and other extra safety measures. On the same note, bear in mind that you are dealing with either propane or natural gases that are very dangerous.

When using propane, the annual cost is $163, and the good thing is that it is widely available. If you want to install a propane model, you will be forced to pay for $498 for installation. On the other hand, when using natural gas, you will purchase it at $163. Also, when it comes to installation, you will be required to pat $429.

As a homeowner note that these tankless water heaters will cost more if you are not well-prepared. When it comes to labor, you are likely to cost up to $1200. Remember that permitting will cost you between $200 and $500 based on the location you intend to install.

How Efficient Are Gas Tankless Water Heaters?

It is critical to note that gas tankless water heaters are efficient because they do not have to pay to keep your water hot. Since all tankless units start heating water when you open a faucet, you will not spend any money when you don’t use hot water.

Tankless water heaters come with a long lifespan in terms of both components and units. But with the annual maintenance, you might not change your fundamental unit for the next twenty years. In other words, you need to understand that regular maintenance will keep your tankless water heater efficient. Moreover, natural propane or gas is cheaper than electricity.

In simpler terms, most gas tankless water heaters can go up to 96% efficiency. On the same note, it is critical to note that most of these tankless water heaters do not go lower than 85% efficiency. Once you choose to buy a water heater, you are likely to save up a lot of money and enjoy this efficient product.

How to Maintain a Gas Tankless Water Heater

Once you have known some of the tools that you need to have for the installation process, make sure that you take your time to understand how to install a gas tankless water heater.

First, ensure that the water heater’s power source is turned off. Turn on and close the available three water valves that are attached to your radiator. Do not forget to attach the hosing lines to each of the three pipes. After doing this, open the purge port valves through the available perpendicular twists. Also, disconnect and remove the hosing lines before you replace the caps of the purge port. After doing all this, you can now restart your water heater.

Since you can safely clean and maintain your gas tankless water heater, it is recommended that you hire a professional to install it for you. With this, you may not encounter more problems with your tankless water heater.

How Much Money Can I Save With a Gas Tankless Water Heater?

The model of your heater will determine the right answer to this question. With the standard tankless water heater, you will save up to 70% off your water heating bill. But when you are using a proper model, note that you might save up to $300 on your tax bill. Therefore, ensure that you make the right choice when choosing your gas tankless water heater.

Can High Altitudes Affect Gas Tankless Water Heater?

Most people believe that most gas water heaters lose efficiency when they are replaced often. Ideally, it is vital to note that a gas unit might lose up to 4% of its effectiveness when its above 100 feet.

Can One Gas Tankless Water Heater Heat My Entire Home?

The answer to this question is yes. We have other types, especially the gas ones that have powerful motors to heat water in your room. Since some models are suited for a single faucet, It is critical to note that you can go for a model that can handle more than two valves. But keep in mind that you need to size your water heater properly to suit your heating needs.

The Installation and Maintenance of Gas Tankless Water Heaters

As stated earlier in our post, for you to install a gas tankless water heater, you need to services of a professional installer. In other words, it is a task that requires someone with enough experience and skills. Unless you are sure that what you are about to do it right, it is recommended that you contact a professional.

For the installation process, make sure that you have power drills, reciprocating saws, tanks, torches, screwdriver sets, adjustable wrenches, and a spade drill bits. Also, ensure that you have sealants, caulk, black pipes, tankless gas, gas connectors, gas fitting, valves, and pipes.


1. How long does it need to heat cold water?

Heating time is closely related to the performance of a water heater; some are made to heat water in a few seconds, while others need 1 or even 2 minutes. But it is also affected greatly by the distance between heater and destination. If you want an extremely short waiting time tankless water heater, you can install it right near the point of use.

2. Will the water temperature be affected by altitude?

Yes, for gas-powered tankless water heater, the gas loses efficiency at a rate of 4% per 1000 feet when it is used at 4000 feet. But for electric tankless water heater, the temperature stays stable and is not affected by it.


Top 3 Best Tankless Water Heaters Best Type
Most Powerful one Rinnai RUC98iN Tankless Water Heater
The lightest type Takagi T-KJr2-OS-NG Tankless Water Heater
The most energy-efficient one Noritz NRC661-DV-NG Tankless Water Heater

The natural gas tankless hot water heater is becoming more and more popular now, many leading brands such as Noritz, Naiven, Takagi, and Rheem, etc. are still doing their best to perfect the performance of gas water heaters. If you have any other troubles in choosing or venting, you can ask the manufacturers directly. Also, if you want to get more information about price or product details, you can check them out on Amazon, it will always meet your demand and offer the best service for you.


Will Montgomery

Will Montgomery: Electro-Mechanical Engineer, Serial Entrepreneur, and Real Estate Enthusiast. Met David at Penn State, where he earned a BS in Electro-Mechanical Engineering and a minor in Business. Expertly manages capital equipment manufacturing, refurbishing, and repair businesses, while exploring opportunities in real estate and advocating for practical heating solutions.

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