Best Gas Tankless Water Heater Reviews

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Thinking about switching to gas tankless water heaters but aren’t sure whether they’re worth the splurge?

Well, I have some good news for you – and some bad.

Bad news first: Gas tankless water heaters are some of the most expensive on the market.

But here’s where the good news starts pouring in: more than a few benefits counteract the hefty price tag.

A keen eye cannot help but notice a few important (and long-term) advantages. Gas-powered tankless water heaters:

  • Provide an endless supply of hot water.
  • Save valuable space for homeowners.
  • Pay for themselves in 6 to 10 years, depending on the model.
  • Last up to 20 years.

Next, most gas-fired tankless water heaters qualify for a $300 tax credit in the U.S.

Look for water heaters with a 0.82 energy factor or those with a thermal efficiency of at least 90 percent to qualify.

Even better, ENERGY STAR certified natural gas-powered tankless water heaters:

  • Use less energy.
  • Protect the environment.
  • Come with lower month-to-month energy costs.

“They can save a family of four $3,500 over their lifetime, and will pay for its additional cost in two years.” Source:

But what are the best tankless water heaters out there?

You’ll find out today.

Most tankless water heaters shortlisted here are ENERGY STAR certified. They’re the best models the water heating industry has seen to date. Now, onto the list.

What Are the Best Gas Tankless Water Heaters on the Market?


Flow rate
Household Size
Rinnai RUC98iN
Rinnai RUC98iN Ultra Series Natural Gas Tankless Water Heater Review
82 lbs.
10” x 18.5” x 26”
9.8 gallons per minute
Large Households
(5+ people)
Check Price
Noritz NRC661-DV-NG
Noritz NRC661 tankless water heaters review
11.42 lbs.
6.7” x 13.8” x 23.6”
6.6 gallons per minute
Mid-sized household
(3 to 5 people)
Check Price
Rheem RTGH-95XLN
Rheem RTG-84XLN outdoor tankless water heater review
78.4 lbs.
18.5” x 9.75” x 27.5”
9.5 gallons per minute
Large Households
(5+ people)
Check Price
Takagi T-K4-OS-NG
Takagi T-K4-OS-NG Outdoor Tankless Water Heater Review
38 lbs.
8.5” x 13.8” x 20.3”
8.0 gallons per minute
Mid-sized household
(3 to 5 people)
Check Price


1. Rinnai RUC98iN Natural Gas-Fired Tankless Water Heater

Rinnai RUC98iN Ultra Series Natural Gas Tankless Water Heater Review

Best Natural Gas-Fired Tankless Water Heater

Rinnai RUC98iN is one of the best tankless water heaters available. Many advanced features are packed into this water heater unit.

Namely, large capacity, coverage of both hot and cold climates, and a strong brand name.

With water flow as high as 9.8 gallons per minute, this indoor Rinnai model will provide hot water for the whole house. It can run five showers or water outlets at the same time!

That said, you can rest easy knowing the unit will supply hot water even if you have a low inlet water temperature.

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Key specs


This gas-fired tankless water heater runs on natural gas or propane, depending on the model. And it’s one of the most powerful water heaters on the market.

Not only can it provide an endless water supply for multiple fixtures, but it can do so while saving energy.

Rinnai RUC98IN is a proud holder of ENERGY STAR certification.

And although it’s on the expensive side, I highly recommend this heater boasting an energy factor of 0.95.

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  • Capable of achieving a temperature rise of 60 ℉.
  • Comes with intuitive temperature control.
  • Designed to save space. You can fit it almost anywhere, or use it as a point of use unit to increase performance and reduce energy loss.

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  • If used for more than one fixture at once, the water temperature may suddenly drop until it’s back on again.
  • Comes with a hefty price tag.

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Compared to other tankless water heaters on our list, the Rinnai is one of the most powerful and the most costly. Yet, it can serve both residential and commercial properties with an endless hot water supply.

This goes hand in hand with high energy efficiency. With this water heater, you can expect to shell out a considerable sum. But once you do, you’ll end up with a lower energy bill, guaranteed.

2. Noritz NRC661-DV-NG Indoor Condensing Direct Tankless Water Heater

Noritz NRC661 tankless water heaters review

Best Value for Money Gas Tankless Heater

The Noritz NRC661-DV-NG is a tankless water heater that runs on natural gas.

It’s engineered by Noritz, the long-time leader in energy savings with over 60 years of experience in the industry.

A good price to value ratio makes this heater a satisfying purchase for most households.

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Key specs


  • The Noritz NRC661-DV-NG comes with a solid heating capacity. It has a volume output of 6.6 gallons per minute. So, homeowners in the southern U.S. can expect this unit to cover the water heating needs for a typical two bathroom home. As for those in the northern U.S, their expectations should be slightly more modest. This is because the unit will provide efficient water heating for a bath and a half in colder climates.
  • This model comes with simple, straightforward installation instructions. So, if you have some hands-on handyman experience, you can lower your installation costs.

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  • Comes with an advanced heat exchanger design, digital display, and a built-in controller.
  • Provides a consistent on-demand water supply with digitally-regulated output temperature.
  • ENERGY STAR rated with 0.89 energy factor. That’s slightly lower than other tankless water heaters on our list. However, that’s still 30 points higher than conventional tank water heaters.

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  • This unit comes under the category of mid-price range tankless water heaters. Still, it’s on the expensive side compared to traditional tank water heaters.
  • You might have some cold water sandwich issues. This is more common with electric water heaters, but it can occur with gas-fired units too. There’s a simple solution for this, though. Install a recirculation loop. This loop will return the cold water back to the system and prevent the issue before it ever ruins your shower.

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The Noritz NRC661-DV-NG tankless water heater is a good value for money unit. It has a decent performance as it can fulfill all the water heating needs for an average household.

Compared to non-condensing water heaters, it doesn’t require a high-temperature vent. Instead, you can use Schedule 40 PVC pipe and fittings which will help you save on installation costs.

3. Rheem RTGH-95XLN

Rheem RTGH-95XLN Prestige Natural Gas

Best Energy Saving Gas Tankless Heater

The Rheem RTGH-95XLN is one of the best tankless water heaters in its class. It’s a powerful, high-efficiency unit that’s also a huge energy saver.

It sets a benchmark for other brands along with the Rinnai RUC98iN, as its energy factor is rated at an impressively high 0.94.

This unit is a perfect choice if you want a powerful machine and considerable energy savings.

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Key specs


  • This Rheem unit scores a pretty high volume output that stands at 9.5 gallons per minute. The advanced flow can provide hot water even for larger households that use multiple appliances.
  • The heater can reach a solid temperature rise of 35 degrees Fahrenheit. This is what makes it a good option for warm and rainy climates.

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  • Rheem RTGH-95XLN is an outdoor tankless water heater that runs on natural gas. As a result, you don’t need to shell out extra money to install a drainage system for ventilation. This is because an outdoor tankless water heater has much shorter venting.
  • This high-efficiency tankless water heater offers more opportunity for installation cost savings. The unit requires a 1/2″ gas line as opposed to most other higher-end heaters – which require 3/4″ gas lines.
  • ENERGY STAR rating and energy efficiency at 94 percent place this water heater at the top of the ladder.

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  • Lower temperature rise
  • Expensive

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The Rheem RTGH-95XLN is one of the most high-priced water heaters on our list. But this is to be expected for all the advanced features you get.

If you ask me, this unit is a perfect fit for those who want all the bells and whistles. It’s also a good option for those who want to remove the hassle of a complicated installation.

4. Takagi T-K4-OS-NG

Best Outdoor Gas Tankless Heater

Takagi T-K4-OS-NG Outdoor Tankless Water Heater Review

The Takagi T-K4-OS-NG tankless water heater is an energy-efficient solution made by Japanese engineers. It runs on natural gas but it’s not ENERGY STAR qualified.

However, it does meet the energy efficiency requirements of the U. S. Department of Energy.

This tankless water heater comes with all the perks of being an outdoor heater. So, you won’t encounter any additional costs when it comes to installation.

Judging by its specs, the unit comes with a moderate price tag for the application coverage it offers.

Key specs icons

Key specs


  • The water heater comes with a high flow rate of up to 8 gallons per minute. Which means it can cover the hot water needs for a medium-sized household. It will also accommodate the hot water needs of a small family with multiple hot water fixtures.
  • It provides an efficient water flow rate for three showers in warmer climates and two showers in colder climates.

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  • Compact design
  • Outlet thermistors for temperature monitoring
  • Built-in freeze protection

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  • Unlike other water heaters out there, you can’t go DIY with installing this Takagi unit. Moreover, all Takagi water heaters must be installed by licensed contractors if you want to make the most of your warranty.

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All taken into account, Takagi T-K4-OS-NG is good value for money. It’s a great domestic hot water system for an average family. You can use it to safely run one shower, one dishwasher, one washing machine, plus the faucets.

How to Choose the Gas Tankless Water Heater That’s Best for You?

Still in a quandary about which tankless water heater is best for your needs? There are a few extra things you should to really hammer home what you’ve read so far.

In short, you want to look for the maximum temperature rise a tankless water heater can achieve at a given flow rate.

To that end, here’s your step-by-step guide:

  1. Figure out how many applications you want to run depending on your hot water needs.
  2. Determine the water flow rate needed to run those applications. You do this by simply adding up the flow rates of each application.
  3. Pinpoint the required water temperature rise. It’s easy – subtract your inlet groundwater temperature from your desired water temperature.

Learn from the example below.

Let’s say you want your water heater to give you a temperature of 106 ℉ and your groundwater temperature is 50 ℉.

In addition, you want a water heater unit that’s capable of powering 2 showers at the same time. You’ll see it in the chart below, but to calculate your GPM, you need to know that a standard shower uses 2.5 gallons per minute.

So, what’s the verdict – how do you size your tankless water heater unit?

You’ll need a water heater that can achieve a 50° temperature rise (106 ° – 50 °) at 5.2 gallons per minute (2.5 + 2.5 GPM). Easy, right? 

Each manufacturer will provide you with a tankless water heater sizing guide. This guide will enable you to put the figure on your water heater easily Now, onto the chart:

Average Hot Water Flow Rate
Average Temperature
Tub 2.5 – 3.0 GPM 104°F
Shower Tub 4.0 GPM 102°F
Washing Machine 2.0 GPM 120°F
Kitchen Sink 1.5 GPM 110°F
Dishwasher 1.5 GPM 110°F

What Is the Best Water Heater for Cold Climates?

If you live in a colder climate, you’ll need a powerful unit. One that can bridge the gap between the inlet and the desired temperatures and still maintain a decent flow rate.

When compared to their electric counterparts, gas-fired tankless water heaters can achieve a higher temperature rise.

So, a typical electric tankless water heater will be able to process 2 gallons per minute at a 70°F water temperature rise. Whereas a gas-fired one will be able to process 5 gallons per minute at the same temperature rise.

What Is the Most Energy Efficient Tankless Water Heater?

Another important point. When selecting a water heater, you don’t only want to size the unit well. You also want a water heater that will provide maximum energy savings.

Most water heaters on our list above are ENERGY STAR qualified. What this means is that they’re some of the best products on the market.

These tankless water heaters are also called “gas condensing heaters”. Let me clarify.

  • A conventional tankless water heater can reach maximum efficiency of 80%. The remaining 20% of the heat in these products gets wasted.
  • This is not the case with condensing water heaters. Because what they do is recycle this surplus heat so your energy waste is negligible.

Your Turn Now

All said and done, tankless water heaters that run on natural gas are true contenders for anyone switching from a tank water heater.

Although they’re not the happiest solution for those with a tight budget, they do bring real benefits in the long run.

Take any of the items featured on our “best” list above. These are some of the most powerful and most energy-saving units available.

I’d say an ENERGY STAR holder is your best bet if you’re intent on effectively reducing your energy bills. And then there’s that tax rebate to cash in on!

If your tank water heater has served you for more than a decade, then it’s time to replace it with a more energy-efficient option.

I also invite you to drop by anytime you need more water heater-related questions answered. I’ve been here for homeowners just like you for more than 3 years.


Featured Image: by Roger Mommaerts