Best Tankless Gas Water Heater, Reviews & Buyers Guide

The popularity of on-demand, tankless water heater systems has increased over the last few years, and gas tankless water heaters are often the favorite choice. Gas tankless systems offer many advantages over electric units, but they also have their share of short comings.

This buyers guide will help you determine if a gas system is best for you, and it'll show you how to buy the best gas tankless water heater that meets your needs.

5 Best Gas Tankless Water Heaters

There's no shortage of choices on the market today, but here are our 5 top picks for the best gas tankless water heater. Each are unique in their design and performance, so you'll want to make sure to take the time to ensure the tankless you choose is a good match for your household hot water needs.

Rheem RTGH-95DVLN Review

This unit get's our vote for the best gas tankless water heater for the indoors!

Rheem's been manufacturing tankless water heaters for a very long time, and the RTGH-95DVLN is an exceptional indoor condensing tankless, our pick for the best gas tankless water heaters available today. It can deliver up to 9.5 gallons of hot water every minute, and for even higher demand situations, two units can be connected with an EZ-Link cable.

Installation and service is easy with Rheem's self-diagnostic system, and it even comes with a digital remote! PVC pipe can be used with the two-pipe direct vent system, and there's a built-in electric blower.

This gas tankless unit is best for homes located in higher elevations as it is capable of performing in altitudes as high as 9,840 feet above sea level, and has freeze protection down to -30°F.

The stainless-steel condensing heat exhanger and intelligent electronic controls helps increase energy efficiency, and the digital display shows the current water temperature and error codes.

If you're looking for a high-performing indoor gas tankless water heater this is one of the best and should definitely be on your short list!

• Delivers up to 9.5 gallons of hot water every minute.
• For high demand homes, two units can be connected together.
• Easy to install and service.
• Designed to perform in high altitudes.
• Freeze protection down to -30°F.
• Intelligent electronic controls.

Rinnai RUC98iN Heater Review

It's hard to go wrong with a Rinnai, and we particularly like the RUC98iN. This indoor condensing tankless water heater is part of Rinnai's Ultra series.

When the temperature rise is 30°, this unit can deliver up to 9.8 gallons of hot water a minute (5.6 gpm at a 60° temp rise). And with a thermal efficiency rating of 95%, it means that nearly all of the energy this system burns will go into heating your water. This unit is even Energy Star certified which is a sign that its one of the best and most economical on the market!

The RUC98iN supports both concentric and twin pipe PVC ventalation, so you have the best of both worlds with twice the venting options without the need of an adapter. In addition, Rinnai includes isolation valves!

With a 12-year warranty on the heat exchanger, 5-year parts, and 1-year labor, Rinnai not only builds an exception tankless, but provides one of the best warranties as well. If you're looking for an indoor natural gas tankless water heater, Rinnai's RUC98iN is a solid choice.

• Up to 9.8-gallons of hot water a minute.
• Thermal energy efficiency (EF) rating: 0.95.
• The heat exchanger comes with a 12-year warranty.

Nortiz EZ98DVNG Review

The Noritz EZ98DVNG gets our vote for the gas tankless water heater with the best warranty!

With it's clean no-nonsense good looks, the Noritz EZ98DVNG can deliver up to 9.8 gallons of hot water a minute, at an impressive .97 UEF rating (efficiency). It's even Energy Star certified!

The EZ98DVNG is one of three models in Nortiz's Easy Series, and this particular model is designed to replace a 50-gallon tank-style water heater. 

Noritz has a reputation of designing their tankless units with ease of installation in mind. The plumbing attachments are located on the top of the unit, and the unit can even be vented using your existing metal venting . . . saving you both time and money.

Nortiz offers one of the best warranties in the industry with a 25-year heat exchanger warranty, and 5-years parts, and 1-year labor.

This tankless unit from Nortiz is a solid performer and should definitely be on your short-list after readign our review. It's ideal for households that are transitioning from a tank-style water heater to a tankless.

• Up to 9.8 gallons of hot water a minute.
• UEF rating 0.97 (energy efficiency).
• Energy Star certified.
• Model replaces a 50-gallon tank system.
• Easy to install, saving you both time and money.
• The heat exchanger comes with a 25-year warranty.

Rheem RTG-95XLN Review

Are you looking for an outdoor unit? The Rheem RTG-95XLN gets our vote for the best outdoor tankless water heater!

If you live in an area that an outdoor tankless water heater makes sense, then you should definitely take a close look at Rheem's RTG-95XLN and our review. At a 35° temperature rise, this unit can produce 9.5 gallons of hot water.

One of the advantages and best things about installing an outdoor tankless water heater, is that you won't need to worry about venting. This makes your installation easier and less expensive. In addition, you'll be able to mount the remote control inside your home and make all of the adjustments from inside your house.

Rheem's RTG-95XLN is part of a series of ultra low NOx, mid-efficiency tankless units. It has a efficiency rating of .81 UEF.

The exclusive Water Savings Setting reduces the flow at the faucet until the set temperature is reached. When this setting is activated, the homeowner can save up to 1,100 gallons of water each year!

And if having instant hot water is your thing, the RTG-95XLN is designed for an optional recirculation pump. There's no shortage of bells-n-whistles with this outdoor unit and it's a solid performer from a company who's been manufacturering water heaters for many, many years.

• Up to 9.5 gallons of hot water a minute.
• Outdoor system so you won't need to worry about venting.
• Mid-efficiency tankless unit. It has an energy efficiency rating of 0.81 UEF.
• Water Savings Setting can save a home up to 1,100 gallons of water each year.

Rinnai RUR199iN Review

If you have a household that has high hot water needs, the Rinnai RUR199iN is best for high performance demands!

The SENSEI RUR199iN Super High Efficiency Plus condensing tankless water heater from Rinnai is Energy Star certifiied and has a .93 Uniform Energy Factor.

It can deliver up to 11 gallons of hot water every minute, and is Ultra Low NOx. The RUR199iN uses Circ-Logic recirculation technology which allows you to program your patterns so you'll have hot water available when you'll need it, and you won't need to circulate when there isn't a demand.

The unit can operate in altitudes up to 10,200 ft, and Automatic frost protection means you won't need to worry when the weather turns cold.

By itself, this unit has plenty of features, but there are also many optional accessories you can add to customize your tankless. The RUR199iN is a powerful unit built for demanding households, but there are smaller models in this line-up if you don't need a tankless that can deliver 11 gallons per minute.

• Energy Star certified.
• 0.93 Uniform Energy Factor (UEF).
• Capable of delivering up to 11-gallons of hot water every minute.
• Program your hot water patterns so you only heat when needed, thus saving you money.
• High altitude and automatic frost protection.
• Many optional add-ons to customize your home system.

Cost of Gas Tankless Water Heaters

How to Buy a Gas Tankless Water Heater for Your Home

There's a lot to consider when it comes to buying a tankless water heater, and it's easy to get overwhelmed. Whether your building a new home or replacing an old unit, purchasing a system that can meet your household's hot water needs is critical.

This article will help you find the right tankless gas water heater for your home. You'll have the knowledge you need to research and compare appliances, so there won't be any surprises down the road. 

If you're still on the fence about whether to buy a gas or electric system, check out our article Gas vs Electric Tankless Water Heater to see a full comparison between the two.

How a Gas Tankless Water Heater Works

Tankless units are often called on-demand water heaters because they only operate when there's a need for hot water. When a hot water tap is opened, cold water flows into the tankless water heater and triggers the gas burner to jump into action.

The cold water is warmed as it travels through the heat exchanger, where heat is transferred to the water. Then the hot water flows from the tankless and enters your plumbing to be delivered to the open hot water fixture.

No Storage Tank Limits for Tankless Water Heaters

Where a tank-style water heater can only deliver as much hot water as the size of it's tank, an on-demand tankless system is capable of delivering a seemingly endless  stream of hot water. 

Unlike a storage tank, where hot water is held in an enclosed container full of sediment and rust, a tankless water heater always delivers fresh hot water.

Choose the Correct Size Tankless Water Heater

Although tankless water heaters aren't restricted by tank size, they are limited by flow rate. This means that there's less room for error when you select the size of your tankless water heater.

A tank-style water heater uses a storage tank to hold a reserve of hot water, but an on-demand system doesn't have this buffer. If the household demand exceeds the appliance's ability to heat water, the unit will be forced to deliver lukewarm water.

Correctly sizing your tankless water heater will ensure that you purchase a heater that's capable of meeting your household hot water needs.

Selecting the Right Size Gas Tankless Water Heater

Tankless water heater systems are sized by the amount of water the unit is capable of heating at any given time. This is called flow rate, and it's a critical factor when shopping for a tankless.

If you purchase a tankless water heater system that has too low of a flow rate to meet your household's hot water demands, the unit won't be capable of delivering enough hot water. Nobody likes a cold shower, so it's critical that you select a tankless unit that's large enough to deliver hot water during your family's peak usage.

How to Determine the Right Size Tankless Water Heater

1. Temperature Rise: The difference between the incoming ground water temperature and the heated output temperature.
2. Flow Rate: The amount of water a tankless water heater is capable of heating at any given time.

All manufacturers size their tankless models using both these two factors. If you know these two numbers, you'll be able to speak the same language as the manufacturers. Although, each manufacturer's approach may differ slightly, you'll still be able to compare apples-to-apples.

Temperature Rise

To determine the temperature rise you'll need to know two numbers: The incoming water temperature, and your desired hot water temperature.

To find the incoming water temperature you can use this chart and simply locate where you live, then jot down the corresponding temperature.

Next, you need your desired hot water temperature. Most people set their water heater between 110-to-120 degrees Fahrenheit, but if you like your hot water slightly warmer or cooler you should use that number instead.

The difference between the two numbers is your temperature rise. As an example; if your incoming water temperature is 47F and your desired hot water temperature is 120F, your temperature rise will be 73 degrees (120 - 47 = 73).

Your tankless system will need to heat the cold incoming water 73 degrees in order to reach the desired hot water temperature of 120 degrees.

Flow Rate

Finding the correct flow rate for your hot water needs is easier than you  might think. First, determine when your household uses the most hot water. This is called peak demand and in most cases, the peak demand is in the morning when people are showering and getting ready for school or work.

Next, count the number of open faucets and appliances used during a typical peak demand period. Do you frequently run the clothes washer during this time? The dishwasher? How many people are showering? Are any sinks used?

Since flow rate is measured in gallons per minute (GPM), you'll need to know the GPM for each fixture or appliance being used during peak demand. Here's a handy chart to help:

If you typically run 1 shower (2.5 gpm) and a washing machine (3.0 gpm), your peak hour gpm would be 5.5. Using the example above, you would need to purchase a tankless water heater that could deliver 5.5-gallons of hot water per minute (gpm) with a temperature rise of 73-degrees.

Does the incoming water temperature really matter to the tankless water heater's flow rate? Well, let's take a look at a real life example:

The Rheem RTGH-95 is a powerful indoor tankless unit that's capable (and advertised) of delivering 9.5 gallons of hot water per minute (GPM). But in order for the appliance to hit 9.5 GPM the RTGH-95 only needs to raise the water temperature by 35 degrees. 

If you live in an area where the typical temperature rise is 70 degrees, the RTGH-95 will only deliver 5.5 GPM. This is still a respectable performance, but if your hot water needs are 9.0 GPM, this unit will be undersized for your home.

The chart below shows how Rheem's RTGH-95 performs with various temperature levels. This is true with all tankless systems and its why knowing your hot water requirements is so important when selecting a tankless system.

Watch the Video:

British Thermal Unit (Btu)

Another factor that should be considered is Btu. The U.S Energy Information Administration defines Btu as "the quantity of heat required to raise the temperature of one pound of liquid water by 1 degree Fahrenheit at the temperature that water has its greatest density (approximately 39 degrees Fahrenheit)."

When shopping for a the best gas tankless water heater always purchase the one that can deliver the highest Btus for your required flow rate.

As an example, if you need a tankless that can deliver a flow rate of 5.5 gpm at a temperature rise of 70-degrees, and you've found two models you like, select the one with the higher Btu rating. It'll be capable of delivering more power.

Gas Fueled Tankless Hot Water Heaters

Uniform Energy Factor

Before June 2017 gas tankless water heater's efficiency was measured using an Energy Factor (EF) rating. Today, the Uniform Energy Factor (UEF) is now the standard for measuring energy efficiency.

The UEF is thought to be a better representation of how the consumer uses hot water. There are three criteria used during the testing to determine the UEF rating: First hour rating/first hour delivery, capacity, and estimated energy costs.

Appliances with a high UEF rating will offer more energy savings since the unit will operate more energy efficiently.

Fuel Supply Line

The fuel supply line is the gas line that leads into your house and connects to the tankless unit. This line must be able to provide enough fuel for the large burners to deliver instantaneous hot water.

A tank-style gas water heater will have an output in the range of 75,000 Btu/h. But a tankless unit is frequently more than double that amount, and may require up to 200,000 Btu/h.

Direct Ignition

• A direct ignition system delivers a spark to the main burner when it detects water flow.
• These systems offer significantly improved energy efficiency over a standing pilot light.
• Depending on the design, the unit either requires an electrical outlet nearby or cell batteries to operate.

Hydro-Power Ignition

• The burner is ignited when water flows into the unit and activates a small turbine.
• Does not require an electrical connection or battery to operate.
• Manufactured by Bosch.

Venting

Gas tankless water heaters need air to carry out combustion. Once combustion occurs the exhaust needs to be directed outside through a vent. There are two venting methods available for indoor models: Direct vent and power vent.

Direct Vent

• Air is drawn from outside the house into the tankless water heater for combustion.
• There may be two vents: One for air intake and the other for exhaust. OR, one single concentric vent which contains both the intake and exhaust.
• A direct vent system allows the tankless unit to be installed in smaller areas.

Power Vent

• The air inside the house is drawn into the unit for combustion.
• The exhaust is vented outside.
• the tankless must be installed in an area that provides adequate air flow for combustion.

Concentric Venting: Some tankless units use two ventilation pipes, one for the air intake and the other for exhaust. But this is not always the case. It's not uncommon to see a single ventilation pipe used if the manufactuter offers concentric venting.

Concentric venting is a single pipe that contains both the exhaust vent and the air intake. Concentric vents are typically several inches larger in diameter, but they're also safer and easier to install.

Types of Gas Tankless Water Heaters

There are 3 basic types of gas tankless water heaters:

1. Non-condensing tankless water heaters
2. Condensing tankless water heaters
3. Outdoor tankless water heaters

Non-Condensing Tankless Water Heaters

Venting Requirements

Non-condensing gas tankless systems use a more complex venting system than what's used for tank-style water heaters. However, there's more flexibility, since the venting can run vertically through the roof or horizontally thru a side wall.

Due to lower combustion efficiency (lower UEF rating), condensation develops inside the venting. The condensation is highly acidic and standard venting material would be quickly "eaten" away. 

The Category III venting material required is corrosive-resistant and made from stainless steel. As you might imagine, it's more expensive than the standard venting used with tank-style water heaters.

Condensing Tankless Water Heaters

Condensing tankless water heaters offer a more sophisticated venting option. They are more expensive to purchase, but less expensive to install.

Venting Requirements

Condensing tankless systems don't require expensive Category III venting, because they are more efficient than non-condensing systems. Where a non-condensing system may achieve a UEF rating of around 80, a condensing system is in the mid 90's.

When a tankless system runs more efficiently, the exhaust gas temperature is lower and less expensive venting can be used. Materials such a PVC or polypropylene can easily handle the exhaust of a condensing tankless.

Although, you'll typically pay more for a condensing tankless system, your installation costs will be less. In the end, it's far more cost effective to purchase a condensing tankless water heater. You'll save money on installation and the unit will run more efficiently.

• A condensing unit extracts the heat from the exhaust and eliminates the need for expensive venting.
• Condensing units achieve a higher UEF (efficiency) rating. Generally in the mid-to-high 90's.
• Although, condensing units are more expensive than non-condensing units, the upfront expense is offset by the lower fuel costs needed to operate the unit. In addition, installation costs are less since expensive venting isn't required.

This video shows how a Condensing Tankless Water Heater Works:

Watch the Video

Outdoor Tankless Water Heater

An outdoor tankless water heater is designed to endure the weather. They are installed on the exterior of the house and can use  the free air flow outside to vent exhaust. In other words, no additional venting is needed.

If you live in an area where an outdoor unit makes sense, this can be a great choice especially if your house is already built and you're transitioning to a tankless water heating system.

Since these models are located outside, they're generally easier and less expensive to install since venting isn't necessary and fewer modifications will need to be done to your home. 

More and more new homes are being built with tankless water heaters, and as their popularity increases, many homeowners are making the switch as well.

Gas tankless appliances have many positive selling points that make them a better investment than a tank-style water heater. But with that said, they do have their shortcomings, and they are not the best fit for every situation. 

Advantages of Going Tankless

Here's a few of the advantages of switching to a gas tankless water heater:

• Requires Less Space - Since on-demand water heating systems are designed to be installed onto a wall, they take up far less space than a tank-style water heater. If you purchase an outdoor model you'll hardly even know it's there!
• Unlimited Supply of Hot Water - A tankless unit can deliver hot without interruption on a seemingly endless basis. Without a storage tank to limit the amount of hot water it can deliver, you'll no longer need to worry about running out of hot water when you take your shower!
• Lower Utility Bills - Since a tankless water heater is only working when there's a need for hot water, you'll notice a savings on your monthly utility bills. Unlike a tank-style water heater that needs to cycle on and off to keep the tank of water hot, tankless systems don't have any standby heat loss.
• Cleaner Water - Have you ever drained a tank-style water heater? Sediment collects within the tank and settles at the bottom, leaving your hot water in a mucky mess. A tankless water heater draws clean cold water, immediately heats it, and then sends it to the shower or fixture. The water is always fresh and clean, not to mention you won't need to worry about the Legionella bacteria!
• Long Service Life - Tankless water heaters are designed to last. Since the parts are replaceable, if something wears out, a new part can be installed. If you take care of your tankless, it can deliver piping hot water for 20 years or more!
• Peace of Mind - You won't need to worry about 50+ gallons of hot water swamping your floor if the tank fails.

Disadvantages of Going Tankless

Tankless water heaters are an excellent investment, but they do have some drawbacks. Here's a few of the disadvantages:

• Initial Cost - A quality gas tankless water heater isn't cheap. In fact, when you add in installation costs, the initial cost could be 3x's the amount of a tank-style water heater. And, although you'll save money on your utility bills, it'll take awhile to recoup the added expense. 
• Less Room for Error - If your tankless isn't sized correctly it may not be able to meet your hot water demands. Just read a few Amazon reviews and you'll find plenty of homeowners who have "under performing" tankless systems. Take the time upfront or consult with a professional to make sure you purchase the right size for your household. It's a big investment and you'll want to get it right the first time!
• Installation - Installation can be expensive and complicated. Most manufacturers require professional installation for a valid warranty.

Technology and Tankless Systems

As great as a tankless water heaters are today, manufacturers keep adding new features to make them even better. Here are a few things to look for:

Recirculating System Heaters

Although an on-demand system may start working within seconds of a tap opening, it's still going to take about 15 seconds for the water to heat. Then the hot water will need to travel through your plumbing system.

Your instantaneous hot water isn't going to seem very instant!

Some homeowners add a point-of-use water heater in a bathroom or kitchen. This set up can deliver hot water until your main water heater can take over. If your primary water heater is in good working order and doesn't need to be replaced, this is a good plan.

However, if you're buying a new whole house tankless, you should consider purchasing one with a built-in recirculation pump. A recirculation pump can save up to 12,000 gallons of water every year!

Once the pump is activated the cold water within the hot water pipes will return to the water heater to be reheated (instead of going down the drain).

The pump will run for about 60 seconds and then shut off once the pipes are filled with hot water.  Within seconds of opening the tap, your water will be steaming hot.

Becoming Smart

Many high-end tankless systems are wi-fi enabled so you'll be able to monitor and adjust the appliance through an app on your phone.

Rinnai tankless systems offer an optional Control-R module which will connect to Amazon Alexa, Google Home, and Samsung SmartThings.

You'll be able to give a voice command when you want to take a shower, or add it to Samsung's morning wake-up routine and your tankless will begin circulating hot water, so the second you open the faucet the water will be hot.

In addition, you'll be able to change the temperature settings directly from your phone, and monitor the amount of gas your appliance uses and how many gallons of hot water it delivers.

Troubleshooting

Being able to verbally communicate with your tankless unit is a nice feature, but the real benefits of a wi-fi enabled tankless is in troubleshooting.

If your appliance throws an error code you'll receive an alert on your phone and know exactly what's going on. You can even register the unit with an authorized repair center who will also receive the error code. When the plumber arrives to work on your unit, he'll know exactly what the problem is and what parts he'll need.

Gas Tankless Water Heater Maintenance

Like any water heater, tankless systems require regular maintenance. You should always check your tankless water heater owner's manual for specific maintenance requirements and recommendations. 

There are many maintenance tasks such as flushing the unit, that can be done by the homeowner. You might want to consider having a professional perform the maintenance tasks the first time.

You'll be able to watch, ask questions, and take notes. When it comes time to perform maintenance again, you'll know exactly what needs to be done.

Flushing Your Tankless Water Heater

Probably the single most important task to complete is flushing your tankless. As the unit is used, limescale will build-up inside. If the water is hard where you live, you'll need to flush your unit more frequently.

Higher-end systems are frequently designed to resist lime scale, and some units will even alert you when maintenance is necessary.

>>Read our article on How to Flush a Tankless Water Heater<<

Some manufacturers include isolator valves (also called service valves) with their tankless units, and some plumbers will automatically install them regardless if they're included or not.

We highly recommend having service valves installed on your tankless, and although you can add them at any point, the best time is when you install your water heater. They're well worth the investment since they'll make flushing your tankless so much easier.

Sediment Filters

All tankless water heaters have an inlet filter on the incoming water supply line to prevent sediment from entering the unit. But to rely solely on this small mesh screen is a big gamble. 

A tank-style water heater will collect the sediment at the bottom of the tank. But a tankless heater doesn't have anywhere to store the sediment. You can run into all kinds of problems if sediment enters the tankless, and the unit can malfunction and require repairs.

Adding a pre-filter to the incoming water line leading to your tankless provides an added layer of protection from the dangerous hazards of sediment. A pre-filter will remove debris from the water before it enters your water heater.

Adding a sediment filter is quick, relatively easy, and inexpensive. There are several different types available. This article on sediment filters will help you find the one that best meets your needs.

Minimize Lime Scale Build-up in Your Tankless Water Heater

Whether you live in an area with hard water or not, your tankless will develop limescale. Flushing your tankless removes it, but what if you could prevent it altogether?

In truth, that's not going to happen, but you can minimize and slow down the build-up by installing an Aqua-Pure Hot Water System Protector on the incoming cold water line.

The Aqua-Pure filter will bind the calcium and magnesium within the water to help prevent them from developing limescale within your tankless.

Have Your Tankless Unit Inspected by a Professional

Even with performing regular maintenance, a gas tankless water heater should be inspected annually by a trained professional. He'll be able to verify that combustion is occurring safely and that the unit is performing as expected.