5 Best Tankless Gas Water Heater Reviews And 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.

Top 4 Tankless Gas Water Heater of 2019

#1. Rinnai RUC98iN Ultra
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#2. Rheem RTG-95XLN
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#3. Takagi T-KJr2-OS-NG
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#4. Noritz NRC661-DV-NG
best gas tankless water heater review

Best Tankless Gas Water Heaters on The Market

1. Rinnai RUC98iN Ultra Natural Gas Tankless Water Heater

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best tankless gas water heater reviews




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 whole-house 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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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 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.

>Click here to get more indoor gas tankless water heater

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.

>Click here to get more outdoor gas tankless water heater


1. Whole-home tankless gas water heater

When taking a bath, doing laundries 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 whole house 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.

>Click here to get more whole house tankless gas water heater

2. Portable tankless gas water heater

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.

>Click here to get more portable tankless water heater 

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best natural gas tankless water heater

Top 3 Best Tankless Gas Water Heaters

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 cold climate
  4. More safe in using


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

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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  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 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 a 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.

>Click here to check more cheapest gas water heater


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 HeatersBest Type
Most Powerful oneRinnai RUC98iN Tankless Water Heater
The lightest typeTakagi T-KJr2-OS-NG Tankless Water Heater
The most energy-efficient oneNoritz 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 products details, you can check them out on Amazon, it will always meet your demand and offer the best service for you.