The Best Tankless Gas Water Heater for 2021

In this no nonsense review of the best tankless gas water heater for your home, we’ll guide you through the most important and relevant information that you need to know, helping you to understand exactly what to expect performance wise from a whole house tankless gas water heating system.

We know that it might seem confusing at first when it comes to selecting the best tankless gas water heater that’s right for your needs.

You’ll want a tankless hot water heater that’s going to produce enough continuous hot water when you want it, without you having to worry about the hot water flow rate dropping if you turn on additional hot water outlets.

We’ve selected the best tankless gas water heaters available and reviewed them for you so that you can choose the best water heater for your own home requirements.

Best Tankless Gas Water HeaterBrand
Best for Large size HouseholdsRinnai RU199iN
Best for Medium to Large Size HouseholdsNoritz NRC66DVNG
Best for Small to Medium Size HouseholdsRheem RTGH-68DVLN-2

The Best Tankless Gas Water Heaters Reviewed

The following recommended tankless gas water heaters are designed for indoor use only, if you require an outdoor rated tankless gas water heater then check out our review on the best outdoor tankless gas water heaters.

Best for Large size Households: Rinnai RU199iN

This whole house tankless gas water heater is a hot water monster, with an incredible 11 gallons per minute (GPM) of hot water available as and when you want it.

That does sound amazing but, and there always seems to be abut” doesn’t there? In order to achieve the quoted flow rate remember certain criteria has to be met. First off your incoming water temperature plays a massive part in how much flow rate you can really expect to achieve when that incoming water has been heated up.

Making sure you have the right size gas supply coming into the tankless water is extremely important, lots of low output flow problems arise from an inadequate incoming gas supply. Not enough gas feeding into the heater means that the water isn’t going to get heated as quickly as it should.

If you are looking to get this tankless gas water heater installed professionally, as we always recommend you should do, then you’ll be informed by your installer as to what to expect flow wise from this water heater and if there are any improvements to the incoming water or gas supplies needed to help improve GPM flow rate. If improvements are needed then that is something you will need to discuss with the installer.

The Rinnai RU199iN is such a powerful indoor whole house on demand tankless gas water heater that up to 7 outlets can be served with constant hot water as and when you want it, so whether you are showering, bathing, washing the dishes or doing the laundry, you won’t need to worry about running out of hot water.

A a good point to note here is that you have the option of using an external circulating water pump with this system. Circ Logic technology is a great feature and virtually eliminates any waiting time for the hot water to flow out of the appliance or outlet.

If you are not use to using a condensing tankless water heating system then you may be under the impression that you will get instant hot water as soon as the faucet is opened, this is not always the case, remember the hot water has to travel along the pipes to the outlet point, so it has to push through all of the cooler water that’s already in the pipes before you get the hot water.

If you want to eliminate that waiting time then that’s where the external circulating pump comes in. The pump will keep that hot water flowing around the pipes and provide you with constant hot water as soon as you turn the faucet or outlet on.

If adding the circulation pump feature is something that you would like then speak to your installer and he will advise you as to the best way of achieving this. Additional pipe runs may have to be installed to allow for the circulation pump system.

PRODUCT INFORMATION

Rinnai RU199iN DimensionsInches
Width18.5
Depth11.4
Height26.4

Indoor and outdoor wall mounted versions of this tankless gas water heater are available to buy. This model is backed by a residential factory warranty of 180 months or 12,000 operational hours cover on the heat exchanger, 60 months parts cover and 12 months labor cover.

Further InformationRinnai RU199iN
Gas Consumption (Btu/h) Min – Max15,000 – 199,000
Minimum Flow Rate 0.26 GPM
Weight64 lbs
Sound Level48 dB
Gas Supply3/4 Inch
Cold water Inlet3/4 Inch
Hot Water Outlet 3/4 Inch
Condensate Drain1/2 Inch

Although this is a tankless gas water heater you will still have to have an electrical supply at the heater to run the controls.

Electrical InformationRinnai RU199iN
Normal84 Watts
Standby1.3 Watts
Max Current4 Amps
Fuse10 Amps
Freeze Protection148 Watts

Venting Options

There are various venting options to help with the installation process, your installer should be able to advise you on the best venting option to use.

  • Direct venting – Concentric and twin pipe
  • Concentric or schedule 40 PVC/CPVC
  • Non direct venting
  • Common vent

Listed in the table below is the maximum equivalent vent lengths for Concentric.

Venting size2 Inch X 4 Inch3 Inch X 5 Inch
Venting length65 ft150 ft

Listed in the table below is the maximum equivalent vent lengths for Twin Pipe.

Venting size2 Inch3 Inch
Venting length65 ft150 ft

Venting your tankless gas water heater correctly is extremely important, so always be guided by the manufactures recommended venting instructions that relate to your specific model.

Also included in the package are the all important isolation service valves and a pressure relief valve. These valves aid the service process greatly and are an essential part of the installation process, enabling easier preventative maintenance tasks like flushing the system out annually to keep the Rinnai RU199iN tankless gas water heater running efficiently.

What We Like:

  • Endless Amounts Of Hot Water – No more running out of hot water with this powerful tankless gas water heater with up to 11 GPM of hot water on demand available.
  • Circ Logic technology – You can adapt your system to incorporate this recirculation system so that hot water is ready to flow from your outlets instantly.
  • Great Warranty – 15 years on the heat exchanger, 5 years on parts and 1 year covering labor.

Things To Consider:

  • Professional Install – We recommend that you get this top of the line Tankless gas water heater installed professionally, that way you should be able to get the best possible performance from this tankless water heater.
  • Instant Hot Water – If you truly want instant hot water then you’ll need to go for the Circ Logic technology set up, this may involve additional pipe work being added to your current system.

Best for Medium to Large Size Households: Noritz NRC66DVNG

Supplying you with endless hot water on demand, the Noritz tankless gas water heater is a condensing, highly efficient unit (rated at 93 per cent efficiency) that is an ideal choice for medium to large sized households.

Boasting an advanced heat exchanger design and in built controller this water heater will produce flow rates of up to 6.5 gallons per minute of hot water.

With the in built temperature display that you can preset the output temperature to 120°F, 135°F, or as high as 140°F in you like.

This is a direct vent model with numerous venting options available using 3 inch schedule 40/80 PVC, PP or CPVC if you prefer for ease of installation.

A 6 ft length of power cord is included to assist with hooking this tankless gas water heater up to a suitable power supply for the internal control circuit needs, but you’ll need to purchase the valve kit separately for the install.

Suitable for indoor installation only, this wall mounted tankless water heater won’t eat into valuable space like a tank type water heater does.

Safety wise, there’s a flame sensor, overheat device, lighting protection, freezing protection, fan rotation detector and a condensate overfill detector.

Product Information

Noritz NRC661-DV-NG DimensionsInches
Width13.8
Depth6.7
Height23.6

And for your peace of mind this gas tankless water heater comes with a 12 year heat exchanger warranty, 5 years parts and 1 year labor cover.

Further InformationNoritz NRC661-DV-NG
Gas Consumption (Btu/h) Min – Max15,000 – 120,000
Flow Rate0.5 – 6.5 GPM
Weight38 lbs
Water Inlet3/4 inch
Hot Water Outlet3/4 inch
Gas Inlet1/2 inch
Condensate Drain 1/2 inch

This package comes with a 6 ft length of cord for the electrical connection, we recommend that it’s always best to get professional help in when it comes to electrics.

Electrical InformationNoritz NRC661-DV-NG
Supply Power120 Volts at 60 Hz
Power Usage54 Watts
Freeze Prevention138 Watts
Max Current 4 Amps

What We Like:

  • Impressive GPM – At up to 6.5 gallons per minute possible you won’t be taking any cold showers soon.
  • Advanced Heat Exchanger – Controlling the hot water is easy with the advanced heat exchanger and built in controller.
  • Great Bang For Your Buck – Offering great value for money, with excellent performance.

Things To Consider:

  • Flow Rate – Getting the quoted flow rate will depend on factors like incoming water temperature, gas line supply size, and in some cases the out going hot water pipe size too.
  • Instant Hot Water – As with all tankless water heaters, the water does get heated up pretty much instantly, but you may have to wait some time for the hot water to travel along the pipe and flow out of the faucet or appliance especially if it some distance from the water heater.

Best for Small to Medium Size Households: Rheem RTGH-68DVLN-2

When you are looking to buy a tankless water heater for your home it’s most important that you get the sizing right. Sometimes what tends to happen is that a water heater is chosen because it looked like it would do the job, it’s then installed, and it’s only when you come to actually use the water heater that you realise that in fact it isn’t up to the job.

There are various things you can do to ensure you will get exactly what you expected to get from your tankless gas water heater. Knowing the water temperature of the incoming cold water supply helps to calculate flow rate output from the water heater.

Gas supply line size also plays a part in the gallons per hour (GPH) flow rate output, though this generally is more of an issue for the more powerful tankless gas water heater models that quote high output flow rate.

These points may seem difficult to understand if you are unfamiliar with heating systems, so maybe you would prefer to let a professional installer, which is what we always recommend you do, deal with the checks that need to be made to ensure you get the hot water flow rate (GPH) that you need.

This indoor, wall mounted condensing tankless gas water heater will provide you with up to 6.6 GPH of constant on demand hot water, and should quite easily serve 2 bathrooms with constant hot water.

Fully controllable and operating within a temperature range of 85°F right up to 140°F (factory set at 120°F) so that you can get the water temperature just how you like it.

You can even add the recirculation system to ensure you really do have hot water right out of the faucets instantly, although additional pipe work may have to be installed for this facility.

Product Information

Rheem RTGH-68DVLN-2 DimensionsInches
Width18.6
Depth9.75
Height27.5

The included warranty covers a period of 12 years for the heat exchanger, 5 years on parts and 1 year covering all labor costs.

Further InformationRheem RTGH-68DVLN
Gas Consumption (Btu/h) Min – Max11,000 – 120,000
Minimum Flow Rate0.26/0.40 GPM
Maximum Flow Rate6.6 GPM
Weight82 lbs
Water Inlet3/4
Gas Inlet3/4
CondensateBuilt In Neutralizer

We recommend you go for a professional install to make sure that this indoor tankless gas water heater is vented correctly as per the manufactures instructions and guide lines.

What We Like:

  • Excellent Value For Money – You get real bang for your buck with this great value for money tankless gas water heater.
  • Powerful Unit – A very capable tankless water heater, powerful enough to supply 2.5 showers with a constant flow of hot water.
  • Looks After Itself – Self monitoring, self diagnostic system helps to keep the system running smoothly.

Things To Consider:

  • Install And Set Up – Getting a professional installer to take care of the installation should make sure that you get optimum performance from this tankless gas water heater.
  • Add Circulation Pump – Adding a circulation pump and possibly some additional pipe runs will give you hot water more quickly, especially if outlets are quite a distance from the water heater.


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