Best Tankless Gas Water Heaters of 2021

Get hot water in an instant while saving energy with the best tankless gas water heaters.

Have you grown tired of the rising costs of your electric water heater? Or aren’t you getting enough hot water in the winter when you most need it? Tankless gas water heaters are an excellent alternative for households with higher hot water demands.

When comparing gas and electric tankless water heaters, you’ll see a significant difference, particularly in winter performance and annual costs. That is, if you manage to find the right one for your needs. We’ve put together a comprehensive buyer’s guide to help you — plus some of the best tankless gas water heaters currently available.

Our Top Picks

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Product Comparison Table

Product Image of the Rinnai V75IN Tankless Hot Water Heater, 7.5 GPM, Natural Gas, Indoor Installation
Best for Indoors
Rinnai V75IN 7.5 GPM
  • Concentric venting system
  • Temperature lock
  • Works for small to medium homes
Product Image of the Rheem RTGH-95DVLN 9.5 GPM Indoor Direct Vent Tankless Natural Gas Water Heater
Best for Cold Climates
  • Self-diagnostic system
  • Energy efficient
  • Overheat film wrap
Product Image of the Eccotemp i12-LP Water Heater, 4 GPM, Black
Best for The Eco-Minded Family
Eccotemp I12-LP
  • Child locking technology
  • LED screen and touch control display
  • Stainless-steel vent kit
Product Image of the Camplux Tankless Water Heater, 2.64 GPM On Demand Instant Hot Water Heater,Propane Tankless Water Heater for Shower, White
Best for Outdoor Living
Camplux 10L Outdoor
  • For going off the grid
  • Compact and lightweight
  • Includes safety features
Product Image of the Rinnai RUR98iN Ultra Series Condensing Indoor Natural Gas Tankless Water Heater, 9.8 Max
Best for Energy Efficiency
Rinnai RUR98iN
  • Low emissions of nitrogen oxide
  • Extra large water & gas inlets
  • Natural gas or propane powered

How Tankless Gas Water Heaters Work

A tankless gas water heater is significantly more energy-efficient than regular tank heaters and tankless electric units. A regular tank water heater uses a lot of energy to keep the water in the tank at a consistent temperature. It continues to do this even when you’re not home — which results in standby heat loss and wasted cash.

A standard tank gas water heater has burners at the bottom of the tank which heat the water. Although a tankless gas boiler also uses burners, this is where the similarities end.

When you turn on a hot water tap within your home, cold water will begin to run through the tankless unit. As the water passes, a flow sensor activates the burners. These will then proceed to warm the heat exchanger.

The cold water coming into the unit encircles the heat exchanger. This, in turn, heats the water quickly before it leaves the heater. A tankless gas heater features a sealed vent system to allow the combustion gases to dissipate safely (1).

Tankless gas water heaters produce a higher flow rate compared to electric units. However, as energy efficient as tankless heaters are, they’re not without flaw.

A single gas-powered tankless unit can sometimes struggle to keep up with a high demand for hot water. For example, if you’re taking a shower while the dishwasher is running, it might not be able to keep up.

Therefore, if your home requires the simultaneous use of hot water from several outlets, you might need more than one unit (2).

This brings us to the next shortcoming: price. Tankless water heaters are more expensive to purchase compared to regular tank models. That said, they’re inexpensive to use in the long run as your annual utility bills should be significantly lower.

Types of Tankless Gas Water Heaters

For tankless gas water heaters, there are two types to choose from: indoor and outdoor. One of the best things about tankless units is that you can install them almost anywhere.

Storage tank heaters are usually placed in the garage or basement, far away from where hot water is needed. This results in a lot of wasted water as you’re waiting for the hot to arrive. Tankless gas water heaters are compact and can be placed in a cabinet, closet, and even under a sink.

You can also choose an outdoor unit. Let’s take a closer look at the differences.

Indoor Tankless Gas Water Heater

Product Image of the Rinnai V75IN Tankless Hot Water Heater, 7.5 GPM, Natural Gas, Indoor Installation

The indoor system is installed the same way as a regular storage tank unit. The only difference is the missing tank.

Indoor systems are usually mounted to a wall in a location that provides good venting.

An indoor system is a good choice if you live in an area that’s exposed to freezing temperatures during the winter. Having the system indoors can prevent any freezing damage to the unit and pipes.

A tankless water heater tends to create a significant amount of condensation when working. An indoor system, therefore, requires proper drainage availability to avoid any water damages.


  • Space-saving: Indoor tankless water heaters are generally small and compact — perfect for placing close to the faucet or appliance.
  • Protected from harsh weather: Because the unit sits indoors, it’s not exposed to freezing temperatures or hard rainfalls.
  • Minimizes risk of water damage: When installed correctly with a drainage option, an indoor unit can reduce the chances of water damage.


  • Requires proper ventilation: If you don’t have pre-installed venting, you must alter the location to install pipes and vents.

Outdoor Tankless Gas Water Heater

Product Image of the Takagi T-H3J-OS-N Condensing High Efficiency Natural Gas Outdoor Tankless Water Heater, 6.6-Gallon Per Minute

Outdoor systems are usually chosen when ventilation is difficult or impossible to install. The tankless unit is simply mounted to the outside of your house instead of inside.

If you’re planning on changing your storage tank unit to a tankless, we highly recommend an outdoor heater. You won’t need to make as many changes to your home.


  • Easy to install: Since it sits on the outside, you don’t have to worry about creating ventilation. This eliminates any extra costs to alter the structure to fit ventilation.
  • No need for proper drainage: Outdoor units don’t require a good drainage point like an indoor boiler does. However, it’s still recommended to place it near a drain.
  • Less chance for gas or water leaks: Because the unit sits outdoors, you won’t have to worry as much about dangerous or damaging gas and water leaks.


  • Vulnerable to bad weather: Because it sits outdoors, it’s not protected from outside elements like an indoor unit is. If you live in a region that regularly experiences extreme winter cold, an outdoor boiler isn’t for you.
  • Hot water delivery is slower: This is only because there’s a longer distance from boiler to faucet. Fortunately, it shouldn’t be much longer than a minute, depending on your unit and house.

How to Choose Best Tankless Gas Water Heater

To find the best unit to fit your needs, we recommend that you consider a few things:

  • Energy factor: When searching for a tankless unit, look for its Energy Factor (EF) — typically stated on the label. The higher the EF, the more energy-efficient the model is — which spells smaller numbers on your utility bills.
  • Fuel type: It’s between natural gas and propane. Propane is usually the way to go since it uses less energy and has fewer emissions compared to both natural gas and electric (3).
  • Size: You should consider the space which the heater requires when mounted to the wall. Tankless gas heaters tend to be larger than electric models — measuring in the 30-inch by 20-inch range due to the exhaust.
  • Gallons per minute (GPM): These should provide you with 2 to 5 gallons per minute. If your demand for hot water is higher, you might want to find a unit that delivers 8 gallons per minute.
  • Venting: Most tankless gas water heaters will use category III venting since it’s made from stainless steel. These boilers tend to create a significant amount of acidic condensation within the pipes (4).

Did You Know?

A gas-powered unit can provide you with a temperature rise of 70 degrees Fahrenheit at a water flow rate of 5 GPM. Whereas, an electric unit will only give you 2 GPM for the same rise in temperature (5).

The Best Tankless Gas Water Heaters of 2021

Here are our top six tankless gas water heaters on the market.

1. Rinnai V75IN 7.5 GPM Indoor Tankless Gas Water Heater

Best Tankless Gas Water Heater for Indoors

Achieving ultimate energy efficiency is the goal of many of today’s homeowners. Tankless gas water heaters can do just that, and this one from Rinnai is no exception.

One of the reasons why this is at the top of our list is that it produces minimal emissions. Although gas-powered, you can still install it right where you need without worrying about harmful gases. This is thanks to its concentric venting system.

Additionally, this gas boiler uses 40 percent less energy than a traditional tank gas heater. It’s fitted with premium technology that locks in the heat — preventing any accidental changes to the water temperature. No wonder it has an energy factor of 0.82.

It works well as a whole-house heater for small to medium homes. It features durable, efficient heat coils, capable of producing hot water for simultaneous use.

Why We Love It

Features a Concentric Venting System

One of the reasons you can use this boiler indoors is its concentric venting system. Rinnai was one of the first manufacturers to use this special system (6).

It’s pretty much a vent system featuring an outer and inner tube. The inner tube is for the exhaust that transports the used gases out. On the other hand, the outer tube brings fresh air in.

This results in optimal performance and safety by providing a direct-vent and sealed combustion system. The unit releases no harmful gases inside the house, so you and your family can have hot water without compromising safety.

Temperature Lock

To optimize energy efficiency, the unit features a temperature lock. This feature prevents any external factors from meddling with the outlet temperature. In turn, saving energy and water.

Additionally, it can heat the water to a maximum temperature of 160 degrees Fahrenheit. And it only requires 0.4 gallons per minute to activate.

Works Great for Small to Medium Homes

This unit is part of a Value Series from Rinnai. Rinnai usually produces larger boilers — enough for a large home. But now they’ve decided to include smaller units for small to medium-sized homes.

Buying a boiler that’s too powerful for your home will only result in energy and water waste. One of the reasons this unit is ideal for its target market is its durable, efficient heating coils. These enable the unit to maximize output, providing hot water for simultaneous uses — such as sink and shower.

Keep In Mind

Takes a Little Longer to Produce Hot Water

Despite being capable of producing a decent amount of hot water, this compact unit is rather slow. Users pointed out that it took a good 60 seconds before hot water was streaming from the tap.

Additional Specs

Measurements 23 inches by 14 inches by 9 inches
Weight 45.6 pounds
BTU 180,000 BTU
Gas type Natural gas
Flow rate 7.5 gallons per minute

2. Rheem RTGH-95DVLN GPM Tankless Gas Water Heater

Best Tankless Gas Water Heater for Cold Climates

Living up north, where temperatures are usually lower, you need a boiler that’s up to the task. This tankless gas water heater from Rheem might just be it.

One of its features that makes it capable of working through the cold is its freeze protection. This feature will keep the unit protected down to minus 30 degrees Fahrenheit.

Another great feature is the self-diagnostic system. This system shows maintenance codes and temperature settings on an included digital remote control. It indicates issues and alerts you when service is due, and may also assist while installing the unit.

Designed as an indoor boiler, it has a two PVC pipe direct vent-system. Additionally, it features overheat film wrap and is highly energy efficient.

Why We Love It

Freeze Protection Down to Minus 30 Degrees Fahrenheit

One of the features enabling this unit to function in colder climates is its freeze protection. Rheem made the unit with ceramic and copper. The ceramic protects the unit itself, whereas the copper preserves the pipes.

These two materials can keep the unit safe from temperatures ranging from 40 degrees down to minus 30 degrees Fahrenheit. Rheem claims that you can place the unit outdoors because of this feature. However, they still recommend using this as an indoor boiler.

Self-Diagnostic System

The unit comes with a pre-installed self-diagnostic system that will essentially notify you of any issues. Notifications show up on the featured digital remote control and display as different codes from the system. The boiler will even alert you when service is due — usually after it’s been in use for 500 hours.

You can mount the digital remote on the wall next, or close, to the boiler. This makes it easy to regulate the temperature and set it as needed.

Energy Efficient

Rheem is renowned for producing units that are highly energy efficient. This particular model was rated as 94 percent energy efficient. This high number is mainly due to the way Rheem constructed the boiler.

The unit uses up less gas to produce hot water thanks to its stainless steel condensing heat exchanger. Still, it has a huge GPM rate of 9.5 that, Rheem claims, can supply three bathrooms.

Overheat Film Wrap

This is a safety feature that prevents the temperature from reaching a dangerous level. It also keeps the unit safe in case you decide to connect it to another boiler.

Rheem gives you the option of connecting several tankless units to supply households with high hot water demands. If you decide to do this, the overheat film wrap allows for side-to-side combustion clearance. This minimizes the chance of overheating and fire hazards.

Keep In Mind

Can Be Noisy

This unit isn’t as quiet as some of its cousins. Users pointed out that it does make a noticeable sound as it ignites. Fortunately, it doesn’t seem to be too distracting.

Not Easy to Install

This seems to be the biggest issue with many users. The unit requires different pipe fittings and other accessories that, apparently, aren’t included. This can result in several trips back and forth to your local hardware store — or an expensive bill from your plumber.

Along with the unit, Rheem only includes the thermostat and one of the two gas valves needed. So, before you buy the unit, make sure you check what you need in the way of tools and valves.

Additional Specs

Measurements 27.5 inches by 18.5 inches by 9.75 inches
Weight 89 pounds
BTU 199,000 BTU
Gas type Natural gas
Flow rate 9.5 gallons per minute


3. Eccotemp i12-LP Water Heater, 4 GPM

Best Tankless Gas Water Heater for the Eco-Minded Family

The Eccotemp i12 tankless water heater is perfect for the modern small apartment or perhaps the vacation cabin. Eccotemp recommends it for the household that requires hot water for one, or possibly two, applications.

It has quite a unique design with its tempered black glass paneling and touch screen control display. It also features a small LED screen showcasing output temperature and gallon per minute flow rate.

One feature that we love is the child locking technology. We all know touch screens are tempting to a five-year-old.

Additionally, the boiler comes with a stainless-steel, horizontal vent kit. This is ready to install and is delivered with a 110-volt UL power cord.

This unit is an indoor model, and also features an internal exhaust fan.

Why We Love It

Sleek Design

One of the standout traits of this unit is its unique design. It’s sleek and modern to look at with its tempered black glass surface and LED screen. The unit is an indoor model so looks are somewhat important.

LED Screen and Touch Control Display

These are two features which, along with adding to the aesthetic appeal, make it easy to use. On the bottom of the unit, you’ll see “ON/OFF” and “lock,” plus arrows for “up” and “down” to regulate the temperature.

In the middle of the settings sits the LED screen. Here you can see the set temperature as well as the flow rate of gallons per minute. It’s bright and big enough so you can see it from a distance without having to strain your eyes.

Comes With a Stainless-Steel Vent Kit

The venting material is important — the gases used in heaters do have a corrosive nature. This means that if the vent is of poor quality, it could easily break, resulting in a leak. Fortunately, this one is made from stainless steel which is one of the recommended materials to use.

What’s more, the vent kit is located horizontally — making it easy to install.

Features Child Locking Technology

If you’ve got any experience with kids, you know they love to do things they’re not supposed to. One of these could involve touching your tankless gas boiler. Luckily, Eccotemp thought of this and included child locking technology.

Right next to the ON/OFF switch, you’ll see “lock.” Hold this for a few seconds and the unit will lock itself so no small fingers can meddle with the settings.

Keep In Mind

Difficult to Maintain — Doesn’t Do Well With Descaling Treatments

This unit seems to be a bit sensitive to maintenance — especially descaling. Some reviewers said that after doing a descaling treatment with vinegar, the unit started to leak. It turned out that the treatment had punctured one of the internal pipes carrying water.

If you do purchase this unit, make sure you follow directions on maintenance and cleaning.

The Exhaust Pipe Is an Odd Size

Installing seems to be a breeze — until it comes to the exhaust pipe. It seems to be a bit too short for some users. Some reviewers improvised and made an extension using an exhaust pipe from a vehicle.

Additional Specs

Measurements 13.75 inches by 25 inches by 5 inches
Weight 25 pounds
BTU 25,000 to 80,000 BTU
Gas type Liquid propane
Flow rate 4 gallons per minute

4. Camplux 10L Outdoor Portable Propane Tankless Water Heater

Best Tankless Gas Water Heater for Outdoor Living

If you enjoy outdoor life — camping, boating, or a sunny day in the garden — this unit might be for you. Camplux designed this boiler as a portable water heater. It basically consists of the “tank,” a pipe for inlet water, and a hose connected to a showerhead.

What’s great about this unit is that two D cell batteries power its propane gas ignition. This allows you to use it anywhere — even while going off grid camping. It also features an Eco/Full switch.

Additionally, it includes a few simple safety features: flame failure device, dry combustion protection, as well as an anti-freezing system. Considering its power, it’s surprisingly compact and lightweight — easy to move around.

Lastly, it comes with a gas inlet connector, plus a stainless steel vent pipe. It also has a more than ample flow rate of 2.64 gallons per minute.

Why We Love It

Excellent for Going off the Grid

If their name doesn’t give it away, this company is renowned for supplying us with portable boilers. You can use this heater nearly anywhere, be it your cabin, camper, boat, stable, or your backyard. It doesn’t require any electrical hookups as it runs on two D cell batteries that you can easily replace as needed.

The included showerhead and hose simplifies taking a shower or washing your car anywhere you are. The only requirements are propane and a water source that you can connect it to.

Eco to Full Switch

Camplux is also known for providing energy-saving features. This boiler has an “Eco” or “Full” option.

In eco mode, the unit uses less energy and gas by decreasing its flow rate. This is best during warmer seasons — where less heat is necessary.

Full mode, where the boiler uses all its power is the setting to use in colder climes. This will ensure you get the hot water you need.

Includes Safety Features

The product comes with a few safety features to ensure long service life. These include dry combustion protection, flame failure device, and an anti-freeze system.

The flame failure device is especially useful. It prevents any flammable gas from continuing to the burner after the flame is extinguished. Thus avoiding a harmful gas leak.

Compact and Lightweight

Despite the fact that this is one of the company’s larger tankless water heaters, it’s surprisingly lightweight and compact. The boiler measures 20.28 inches high, 12.8 inches wide, and 5.5 inches in depth. It weighs roughly 23.8 pounds.

Of course, it’s not a “carry-with-you” type of boiler like their smaller units. But it’s nonetheless easy to take with you on your camping trip.

Keep In Mind

Water Gets Hot

Yes, I know this is a water heater, but there are reports that the water gets scalding hot. This seems to be an issue especially when you use it on “full” mode.

Additional Specs

Measurements 20.28 inches by 12.8 inches by 5.5 inches
Weight 23.8 pounds
BTU 68,000 BTU
Gas type Propane gas
Flow rate 2.64 gallons per minute

5. Rinnai RUR98iN Indoor Natural Gas Water Heater

Best Energy Efficient Tankless Gas Water Heater

Our last example for today is another model from Rinnai. This model, however, takes energy efficiency to a whole new level thanks to its condensing technology. It’s 95 percent thermal efficient — powered by either natural gas or propane.

This is an indoor unit. Fortunately, though, it has ultra low emissions of nitrogen oxide and meets the Emissions Standards of California and Texas. You can run the unit using either a concentric vent or PVC.

One thing that’s a bit different with this model is the size of the gas and water inlets. This essentially means that it can provide a larger flow of hot water with less power. In the summer, this boiler can provide enough hot water for three bathrooms and a faucet.

That said, it does draw a significant amount of power during the winter — specifically to keep it from freezing. Additionally, it has a BTU input between 15,200 to 199,000.

Why We Love It

Low Emissions of Nitrogen Oxide

This unit emits very low amounts of nitrogen oxide. It’s built with a condensate system which means that it reuses the same gas to heat new water. The boiler is compliant with the NOx Emissions Standards of Texas and California and safe to install indoors.

Additionally, this tankless gas water heater has an energy factor rating of .95. It has immense power compared to other units and is more than capable of providing an endless flow of hot water.

Works With Either Concentric or PVC Vents

This is an excellent option to be given, seeing that some homeowners prefer one and others another. Twin PVC venting pipes are usually what most people prefer since they’re easier to replace when needed. On the other hand, a concentric venting system only requires a single penetration into the unit, which may be easier for some.

Extra Large Water and Gas Inlets

This is a somewhat unusual, or previously unheard of, feature. Either way, this Rinnai has got it. This supposedly enables the boiler to deliver a stronger flow of hot water.

In fact, it has an impressive flow rate of 9.8 gallons per minute. This should be enough for the whole house, or three showers and a faucet.

Powered by Either Natural Gas or Propane

Here’s another option that is compatible with different preferences. Although a lot of heaters run on natural gas, propane is generally the most popular. As we mentioned in the buyer’s guide, it’s both cheaper and friendlier to the environment.

Keep In Mind

Requires Some Know-How to Install

Not a very easy unit to install yourself, it is recommended to seek professional help.

Additional Specs

Measurements 26 inches by 18.5 inches by 10 inches
Weight 61.7 pounds
BTU 15,200 to 199,000 BTU
Gas type Propane or natural gas
Flow rate 9.8 gallons per minute

Tankless Gas Water Heater Comparison Chart

Product Award Dimensions Weight (lbs) BTU Gas type Flow rate (GPM)
Rinnai V75IN 7.5 For Indoors 23″ x 14″ x 9″ 45.6 180,000 Natural gas 7.5
Rheem RTGH-95DVLN For Cold Climates 27.5″ x18.5″ x 9.75″ 89 199,000 Natural gas 9.5
Eccotemp i12-LP For The Eco-Minded 13.75″ x 25″ x 5″ 25 25,000 – 80,000 Liquid propane 4
Camplux 10L For Outdoor Living 20.28″ x 12.8″ x 5.5″ 23.8 68,000 Propane gas 2.64
Rinnai RUR98iN For Energy Efficiency 26″ x 18.5″ x 10″ 61.7 15,200 – 199,000 Propane/natural gas 9.8

Go With Gas

If you’re looking to replace your old unit, and want to become energy efficient, then tankless gas water heaters are ideal. Because they’re gas-powered, they’ll save on your energy bills as well as reduce your footprint on the environment. These boilers are also the best alternative if you live in a colder region.

Do you have a favorite tankless gas water heater? Please leave your answer, or further questions, below.

Headshot of Peter Gray

About the Author

Peter Gray

Peter has been a homeowner for 35+ years and has always done his own repair and improvement tasks. As a retired plumber, Peter now spends his time teaching others how they can fix leaks, replace faucets, and make home improvements on a budget.