Everyday Home

The Best Natural Gas Tankless Water Heater

For many homeowners, storage tank water heaters (and the bills that come with them) are an unquestioned part of home life. We all need hot water after all, and the convenience of a storage tank can come in handy.

As more and more people start to look at ways of using less energy around the home, however, tankless water heaters are becoming increasingly popular. If you’re concerned about the environment or making long-term savings – and no one says you can’t be concerned about both – they’re a great choice, using less energy than storage tank heaters because they only heat water when it’s needed.

If your storage tank heater is more than 10 years old and you’re thinking about a replacement (which you should be), it’s the perfect time to look at upgrading and going tankless. What’s more, their increasing popularity means greater choice at lower prices: there’s never been a better time to invest in a natural gas tankless water heater.

Below are some of the best models available on the market.

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NameFlow Rate (GPM)Energy Factor(%)Our Rating
Noritz NRC6616.6939.4 / 10
Rinnai RUC98i9.8959.4 / 10
Rheem RTG-64DVLN6.4829.2 / 10
Takagi T-KJr26.6829.2 / 10
Camplux BW4224.2288.59 / 10
Takagi T-H3-DV-N10959 / 10
Eccotemp i12-NG3798.6 / 10

1. Noritz NRC661

Noritz are a Canadian company who have been making water heaters for North America for more than 60 years. The NRC661 is their staple condensing natural gas tankless water heater, marketed by the company as “quality meets value”. Looking at the product’s specifications and price, it’s hard to argue the point: the NRC661 is available for considerably less than most condensing heaters, but it doesn’t look or perform like a budget option.

In fact, an energy factor of 93% is competitive with units that cost a lot more, while the maximum flow rate of 6.6 GPM should provide plenty of hot water for average houses and average-sized families.

The NRC661 is not particularly flashy, but it’s a no-nonsense unit that does what it sets out to do very well, and for a more-than-reasonable price. It even comes complete with its own diagnostic program, allowing it to identify and help you fix most of the common issues with natural gas tankless water heaters, should they occur.

For a quality condensing natural gas tankless water heater at a competitive price, Noritz are hard to beat; and the NRC661 is their flagship model.

  • Noritz boast that the NRC661 is a marriage of quality and value, and a quick comparison of the price of this unit with other condensing natural gas tankless water heaters backs up their claim. Available for considerably less than many condensing heaters, this is nonetheless a quality product made with care and attention to detail.
  • The dual heat exchangers used in this condensing heater recycle heat from the unit’s exhaust, helping it achieve an impressive energy factor of 93%.
  • The PVC venting used on this unit is significantly cheaper – and makes installation a lot easier – than stainless steel ventilation, scoring Noritz further points for price and convenience.
  • The maximum flow rate of 6.6 GPM will comfortably provide hot water from two simultaneous draw points; potentially 3 if you happen to live somewhere with a warm climate. The biggest homes and commercial premises may not find the NRC661 enough to meet their needs, but the rest of us can enjoy hot water coverage that’s more than sufficient.
  • The digital display and diagnostic program on the NRC661 mean you can easily control your water temperature, and quickly and simply troubleshoot any issues as and when they occur.
  • The NRC661 is a low nitrous oxide unit which has been Energy Star approved. If you’re in the market for a natural gas tankless water heater, there are strong financial and environmental reasons for considering this Noritz unit.

2. Rinnai RUC98i

Rinnai are a Japanese manufacturer of high-end heating solutions, and with a long history and presence in the USA they’re a globally-trusted brand who are hard to beat.

The RUC98i is in Rinnai’s Ultra Series, designed to present homeowners and professionals with multiple options for ventilation setup out of the box. The flexibility this gives when installing the unit is not to be underestimated: even if you aren’t doing the installation yourself, the job will be quicker and easier (and therefore should cost you less).

This is not a cheap condensing natural gas tankless water heater, but it is one of the best examples of the type on the market today. An energy factor of 95% is thanks to dual high-end heat exchangers, with a maximum flow rate of 9.8 GPM allowing hot water to be drawn from 3 or even 4 draw points simultaneously.

What’s more, Rinnai have pulled out all the stops for convenience: the RUC98i is smaller than a regular suitcase, giving it a tiny footprint compared to the competition and helping you make the most of the space in your property.

For a high-performing natural gas tankless water heater, the RUC98i is hard to beat: the only question left to ask is whether you’re willing and able to pay the asking price.

  • High-quality dual heat exchangers contribute to the RUC98i’s seriously impressive energy factor of 95%. If you want to help save on your energy bills, it’s hard to beat this supremely efficient bit of Rinnai kit.
  • With a maximum flow rate of up to 9.8 GPM, there’s little question that this natural gas tankless water heater will provide hot water throughout your property, whenever and wherever it’s needed.
  • Rinnai have built this unit to be as convenient as possible, not only while in use but also during installation. The unit’s small footprint means it can be installed in a whole load of nooks and crannies that would be too tight for most competing heaters, while the choice of concentric or PVC venting makes the job of installation that much more straightforward.
  • The RUC98i is a low nitrous oxide unit, certified safe for use in the home (which doesn’t mean you don’t need to invest in a nitrous oxide detector – it’s always better to be safe than sorry).
  • This natural gas tankless water heater is compatible with all Rinnai digital controllers. One isn’t included with the unit as standard, but if you own a Rinnai controller you can rest assured that it will work with all Rinnai units currently on the market today.
  • This is an exceptionally quiet condensing tankless heater, being all but silent anywhere with pre-existing ambient noise. If you’re worried about disruption caused by a noisy unit, Rinnai’s heater is one of the best choices you can make.

3. Rheem RTG-64DVLN

Rheem are a well-known name when it comes to heating and cooling: they make water heaters and air conditioners for the office and for the domestic market.

The RTG-64 range is a series of low nitrous oxide tankless water heaters designed for continuous hot water use: the RTG-64DVLN is the direct-venting version for indoor installation, with the RTG-64XLN being a variant designed for installation outside.

Both RTG-64 heaters are non-condensing tankless water heaters, but they make clever use of Rheem technology to bring their performance closer to some condensing models. The water saving setting means you’ll get a reduced water flow until the heater’s brought it to your desired temperature, minimizing wastage and maximizing efficiency.

The overall energy factor is still 82% (not particularly impressive for non-condensing heaters), but Rheem’s low flow technology means the RTG-64DVLN and RTG-64XLN experience a much lower drop in efficiency when used in short bursts compared to other non-condensing models.

For everyday use around the home, the RTG-64 range should meet most people’s needs without difficulty; and if you want to heat somewhere bigger, up to 6 Rheem units can be connected using the EZ Link cable bundled with the heater.

  • An energy factor of 82% is on the lower side of typical for a non-condensing natural gas tankless water heater, but the water saving setting and low flow technology Rheem have built into the RTG-64 heaters go a long way to enhancing it. You won’t experience big drops in efficiency if you only need short bursts of hot water, and you can even choke down the flow rate until the temperature’s where you want it, to minimize water and energy wastage.
  • The RTG-64 heaters are on the lower end of the price range for non-condensing natural gas tankless water heaters, but they’ve still been built with care and attention to detail. Rheem’s self-diagnostic system means your heater should be able to solve many of its problems without your input, while the digital display and remote control contribute significantly to ease of use and all-round user experience.
  • Rheem have included an EZ Link cable with the RTG-64 heaters, allowing you to connect up to 6 Rheem heaters together to work as a single unit. This is a great option to have, even if you never end up making use of it; and it positions this natural gas tankless water heater as one that’s competitive on both the commercial and domestic markets.
  • The maximum flow rate of 6.4 GPM is impressive, and certainly enough to draw hot water from two points in the house at the same time. If you have two bathrooms, an RTG-64 heater is well worth considering.
  • Rheem have configured these natural gas tankless water heaters to be resistant to freezing in temperatures as low as -30 degrees Fahrenheit. If you have a holiday property in a colder climate and want a heater that’s not going to land you with a big repair bill over winter, an RTG-64 may be the option for you. At the other end of the thermometer, the use of Rheem’s proprietary Guardian OFW coating works to prevent the unit from overheating.

4. Takagi T-KJr2

Takagi have been making tankless water heaters since the 1950’s, and their expertise and innovation over so many decades has allowed them to continue offering quality heaters at competitive prices today.

The T-KJr2 is a non-condensing natural gas tankless water heater designed with the average residential property in mind. With a flow rate of up to 6.6 GPM, it’s more than capable of providing hot water at two simultaneous draw points (e.g. two bathrooms), and while the energy factor of 82% may be lower than the condensing water heaters on the market, it will still be a marked step up on using a storage tank heater for your home.

Takagi haven’t skimped on the features, either: the T-KJr2 comes with its own remote control and a whole host of safety features, including emergency shutoff in case of freezing or overheating. What’s more, consumers have praised Takagi for the thoroughness and clarity of the T-KJr2’s installation manual, so if you’re set on installing your heater yourself, this is one of the most straightforward (and reliable) heaters going.

  • A flow rate of 6.6 GPM is more than enough for drawing water from 2 points simultaneously, and so is suitable for a house with up to 2 bathrooms.
  • The energy factor of 82% on the T-KJr2 is on the lower end for non-condensing tankless water heaters, but not so much so that you’ll notice a difference compared to its direct competitors. Condensing water heaters will always be the more efficient, but more expensive, choice; and storage tank heaters are by far the least efficient option.
  • Takagi have bundled a remote control and power cord with the T-KJr2, ensuring that it’s ready to go as soon as it’s installed.
  • The T-KJr2 comes with a raft of safety features: if the heater gets too hot or cold it’ll shut itself down to avoid damage, and the same happens in the case of an electrical surge. Takagi have even built in a number of diagnostic codes, so that the T-KJr2 can identify and fix many of the most common water heater problems on its own.
  • The T-KJr2 has very low nitrous oxide output; in the region of <20 parts per million (ppm). For a safe heater to use at home, Takagi have provided an excellent choice.
  • The installation manual is unusually clear and helpful compared to those bundled with some other tankless water heaters. Something of a Takagi trademark, it makes this heater and others from the same brand a good option for homeowners taking the step of installing their heater themselves.

5. Camplux BW422

Camplux are a Chinese manufacturer who make and sell a wide range of outdoor and home appliances.

The 16L Camplux BW422 is a simple non-condensing unit, available at a budget price point, which nonetheless manages to hit some impressive targets. It’s worth noting that this heater is intended for use outdoors – like at a campsite – and can be rigged up to work as a self-contained shower unit. Camplux have even taken the step of including a shower hose and adjustable shower head, meaning it’s ready for use just as soon as it’s set up.

This is a much easier model to install than most natural gas tankless water heaters: simply hook it up to the hot water and you can run the unit on batteries! With a maximum flow rate of just 4.22 GPM, this Camplux heater may not be the most reliable solution for home water heating, but considering the price – and the fact that it still hits an energy factor of 88.5%, more than many non-condensing tankless heaters – this is an impressive and versatile unit that’s well worth considering.

  • The Camplux BW422 is primarily intended for use outdoors, like as an outdoor shower at campsite, but it can certainly be installed and used around the home. The maximum flow rate of 4.22 GPM limits this heater’s usefulness for larger homes, or indeed anywhere hot water will be needed from two draw points simultaneously; but if you have a small apartment or live by yourself, this Camplux heater will meet your hot water needs.
  • Amazingly, Camplux BW422 can be powered using batteries alone: while this may not be the most energy-efficient way to power a natural gas heater, it has the significant upside that you can use it almost as soon as it’s out of the box.
  • Price: available for less than half what most non-condensing natural gas tankless water heaters cost, Camplux have provided a more-than-serviceable product at a frankly surprising price point.
  • The energy factor of 88.5% is more than many non-condensing natural gas tankless water heaters; a doubly-impressive feat when you consider the bargain-basement price of this Camplux unit.
  • Camplux have built a number of safety features into this heater, including automatic shutoff in the event of an electrical surge, or if the unit gets too hot or too cold. This will preserve your heater’s lifespan considerably, as well as avoiding unwelcome bills brought by ruptured water pipes.
  • The heater comes complete with a shower hose and multi-functional shower head, meaning you can immediately set it up as an outdoor shower with ease.
  • A number of consumers have reported positive customer service experiences with Camplux, including dedicated support staff on individual cases. Given the scepticism that exists around some Chinese manufacturers, it’s worth noting that Camplux as a company are helpful and easy to deal with.

6. Takagi T-H3-DV-N

The T-H3-DV-N is one of Takagi’s condensing natural gas tankless water heaters, and a shining example of the efficiency and attention to detail that are synonymous with the Takagi brand.

This is a condensing water heater, which means it uses two heat exchangers, allowing it to recycle heat from the unit’s exhaust to significantly increase the energy efficiency compared to a non-condensing model.

Takagi haven’t settled for less than the best with the T-H3-DV-N: commercial-grade copper alloy and category III stainless steel are used for the heat exchangers, pushing the heater’s energy factor as high as 95% and contributing to a seriously impressive maximum flow rate of 10 GPM. This is enough to give endless hot water to three draw points simultaneously; even more in warmer climates.

If you’re looking at natural gas tankless water heaters for a commercial property, the flow rate can be pushed through the roof with Takagi’s Multi-Unit Controller, allowing you to link up to 20 units to work together.

Whether it’s for the home or the workplace, the T-H3-DV-N is one of the finest examples of a natural gas tankless water heater on the market. It might not be cheap; but sometimes, you get what you pay for.

  • The dual heat exchangers in this condensing natural gas tankless water heater have been made using commercial-grade copper alloy and category III stainless steel, improving the overall energy factor of the unit and ensuring its durability for a long time to come.
  • An energy factor of 95% is higher than the average condensing heater, and worlds away from the efficiency of a storage tank heater. If you want to save the environment, save on your energy bills, or both, the T-H3-DV-N might be the heater for you.
  • A maximum flow rate of 10 GPM means most domestic properties should experience no delays or unexpected cold water with this Takagi product, even if hot water is demanded from 3 or even 4 draw points simultaneously.
  • The Multi-Unit Controller Takagi have included with this heater allows you to link up to 20 units to work together; clearly overkill in almost any home, but a potentially valuable option if you’re considering going tankless at commercial premises.
  • With integrated controls and power cord, emergency shutoff in the event of freezing or overheating, surge protection, and a self-diagnosis program, the T-H3-DV-N has been set up by Takagi to be a safe and long-lasting product that could keep giving you exceptionally high performance for decades.
  • Price: although it’s certainly not a budget option, the price tag on the T-H3-DV-N is actually lower than many condensing natural gas tankless water heaters. Given the overall quality and attention to detail Takagi have put into this unit, this water heater will likely prove to be a wise and money-saving investment over the long run.

7. Eccotemp i12-NG

Eccotemp are a relatively young name in the water heater market, but the i12-NG is an effort to remedy that. This non-condensing natural gas tankless water heater certainly stands out: the black gorilla glass its case is made from looks cool and eye-catching, especially amidst a field of white appliances. The aesthetic is only enhanced by the blue lighting of the digital display, where you can control temperatures precisely to get water as you want it.

The i12-NG is undeniably a better option for smaller homes: with a maximum GPM of 3, you’ll only reliably get steady hot water from a single draw point, which still leaves it as a good option for apartment owners and people living on their own.

The energy factor of 79% may be a little underwhelming for anyone looking to upgrade from a storage tank water heater, but importantly Eccotemp aren’t asking the price of a more powerful machine: the i12-NG is available at a very low price compared to its competition on the non-condensing heater market, so if 3 GPM sounds like a good enough flow rate for you this is a heater worth checking out.

  • The Eccotemp i12-NG has an unusual and attractive appearance, with blue display lighting and a case made almost entirely from black gorilla glass. If you’re installing it somewhere out of the way this won’t be particularly relevant, but if it ends up somewhere on display it’s a better addition to a room than most white-and-steel appliances.
  • Price: the i12-NG is a fair amount cheaper than most non-condensing natural gas tankless water heaters, so if its lower capacity isn’t an issue for you then this is a budget option that’s worth considering.
  • Despite the low price, Eccotemp haven’t skimped on what they’ve built into and included with the i12-NG. Integrated temperature controls and a blue LCD display ensure you’ve got as much control over your water temperature as possible, while the power cord and stainless steel ventilation kit included make installation just that little bit easier.
  • The electronic ignition used by Eccotemp in this heater is quick, convenient and safe; and the absence of a pilot light goes some small way to making up for the relatively low energy factor on this model.

What are Natural Gas Tankless Water Heaters?

Tankless water heaters are more energy-efficient, and take up less space in the home, than storage tank water heaters. This is because storage tank heaters work by heating and then storing water in an insulated tank, which is then piped out to taps and appliances when necessary. This has the advantage of convenience, but has a real energy cost.

Because storage tank heaters keep the water in their tank at a constant high temperature, they’re remarkably energy-inefficient compared to tankless models, which only heat water as required. Large buildings and professional premises will likely not be able to give up their storage tank heaters just yet, due to the relatively large quantities of hot water required at once. But for most homeowners, a tankless water heater is a legitimate alternative that promises to significantly reduce heating bills.

There are three different types of tankless water heater – non-condensing, condensing, and hybrid – and any of them can be powered either electrically or using natural gas. If energy efficiency is your number one concern, and you live somewhere relatively small – a studio apartment, for example – then an electric tankless water heater may be the best choice for you.

For most homeowners, however, an electric tankless water heater will likely prove frustrating: they’re slower to heat water than natural gas heaters, which makes the lack of a hot water reservoir compared to a storage tank heater that much more evident. This is reflected in their lower flow capacity compared to natural gas tankless water heaters: if you’ll be drawing hot water at more than one point at a time, natural gas is the way to go.

Between the three types of tankless water heater available on the market, non-condensing heaters are the earliest model. As a result they may not be as efficient as the more recent designs, but they’re reliable and well-understood by most tradesmen. Non-condensing heaters use a single heat exchanger to raise the water temperature, and achieve an energy factor (EF) of 85% – a marked improvement on storage tank heaters, but notably less than condensing and hybrid models.

Non-condensing heaters are also less efficient on short draws of hot water; when washing your hands, for example. A further complication is that non-condensing heaters require the installation of stainless steel venting, an additional cost on top of what is already a significant purchase, and an even trickier installation job than would otherwise be the case.

Condensing water heaters are the second generation of tankless heaters, using two heat exchangers and reusing the heat from the unit’s exhaust to raise the energy factor to as much as 94% on some models (although, like non-condensing heaters, they struggle with efficiency over short bursts). An additional benefit of condensing heaters is that they can use regular PVC ventilation, making the job of setup a little easier than for non-condensing designs. However, non-condensing heaters are more expensive units to buy in the first place, so the decision between condensing and non-condensing may be a budgetary one as much as anything else.

The third generation of tankless water heaters is what is known as the hybrid heater. Pioneered in the USA, these contain a small hot water reservoir which increases the heater’s efficiency for small draws of water, raising the overall EF on some hybrid models to 96%. They’re also quicker to heat up in the first place, and like condensing heaters work fine with regular PVC ventilation.

As you might expect, however, the newest tech in a marketplace is always the most expensive; and the relative newness of some hybrid models means they’re more likely to have unforeseen issues, and that professionals are less likely to have a quick fix when they do.

Compared to storage tank heaters, all natural gas tankless water heaters are a serious step up in terms of efficiency, so it’s worth thinking about your budget and how your home uses hot water before deciding which type will be best for you.

Why Buy a Natural Gas Tankless Water Heater?

There are a number of good reasons:

  • Energy-efficiency. Switching from a storage tank heater to a good condensing or hybrid natural gas tankless heater could see a saving of as much as 60% on your water heating, or between $200-400 a year. Given the average 30-year lifespan of most tankless heaters, you can count on yours paying for itself long before you’re done using it.
  • Smaller footprint. This is true for your environmental footprint: because tankless heaters only run when you need them to, you’re using less energy, which is good for the environment and your wallet. Tankless water heaters also have a small footprint inside your home, taking up much less space than the hulking storage tanks which dominate and even completely fill smaller rooms.
  • Heat on demand. As long as you’ve done your homework and bought something with sufficient flow capacity (measured in gallons per minute, or GPM) for your home, there’s no need to worry about running out of hot water.
  • Longevity. Tankless water heaters last considerably longer than most storage tank models. While storage tank heaters will need to be replaced every 10-15 years on average, most tankless heaters will last at least twice as long as that. Natural gas tankless water heaters aren’t only an investment for the long term, they’re a time-saver and a stress-reducer too.
  • Go for the upgrade. If it’s about time you replaced your storage tank, it’s worth considering going for the upgrade. A natural gas tankless water heater will cost you more than a storage tank heater, but over its lifespan will more than pay for itself in terms of energy savings.
  • Increase your value. As energy-efficiency becomes an increasingly high-profile issue, the value of fitted energy-efficient appliances like tankless water heaters continues to rise. It’s worth talking to estate agents in your area to get their opinion, but when you consider the energy savings of a tankless heater and the costs involved in getting one properly set up, there’s every reason to make yours a selling point for your property.
  • Go natural. Among tankless water heaters, natural gas wins over electric in almost every situation. If you live in a small studio apartment and want to squeeze every drop of energy efficiency you can out of your water heater, an electric tankless heater might be the way to go. But if you live anywhere larger, natural gas will give you serious energy savings without the frustration of waiting around for your water to get hot.

Things to Consider

If you’ve decided to go for the upgrade, there are a few things to consider:

  • Size. How big is the heater? Size will have an impact on capacity, but remember these aren’t storage tank heaters, so bigger doesn’t necessarily mean better. In fact, one of the selling points of tankless heaters is that they have a much smaller footprint than storage tank models. Think about where you want to store your heater, and look for something that’s a good size to fit.
  • Flow rate. Measured in gallons per minute (GPM), this reflects how many gallons of water a heater can heat per minute. A good rule of thumb for homes is that 4-5 GPM is sufficient flow capacity for a single-bathroom house – if you have more than one bathroom, look for a heater with a GPM of 6 or more.
  • Energy factor (EF). This is a simple measurement of how efficient the heater is. Or, more scientifically, how much of the energy it consumes is transferred to the water as heat. A decent non-condensing tankless heater should have an EF in the mid-to-high eighties, while condensing and hybrid heaters should have an EF well over 90%.
  • Price. Expect to pay upwards of $500 for a non-condensing natural gas tankless water heater, with condensing models costing about twice as much and hybrid heaters even more. When it comes to natural gas tankless water heaters, the total cost almost certainly isn’t limited to the price you pay for the unit itself. Unless you’re a professional yourself, you’ll need expert help installing the heater. Among other tasks, you’ll need to run a gas line and a dedicated power line to the unit, as well as installing ventilation and possibly additional piping. Don’t let this put you off buying one: the increased efficiency of a tankless heater will generate real savings when it’s time to pay your heating bill.
  • Warranty. Natural gas tankless water heaters are supposed to last at least 20 years, and preferably 30 or more. If you’re going to invest your hard-earned cash in one, go with a manufacturer that’s got enough confidence in its heaters to sell them with a long-term warranty.
  • Your needs. As with any serious consumer purchase, it’s worth taking the time to think about your particular needs before starting to compare different models. How many points will you be drawing hot water from? How many will be in use simultaneously? How many people live in your home? What’s its maximum capacity? How many bathrooms do you have? These are some of the questions you can ask, but you know your own needs better than anyone: think about them and you’re bound to be happier with your purchase than you otherwise would have been.

Risks and Warnings

  • Installing a natural gas tankless water heater is a difficult and potentially dangerous job which should be done by professionals. If you’re a professional yourself, you can save some money by going DIY, but otherwise it’s worth paying a little more to get the job done well. Installing a tankless heater involves running gas and electric lines to the unit at the very least, so it’s not something to be taken lightly.
  • To preserve the long lifespan of your heater, you should flush it every once in a while. If you live in a hard water area, once a year is ideal; otherwise, you can get away with once every 2-3 years.
  • Have your tankless water heater inspected regularly, to keep it safe and make sure you can keep enjoying its energy savings for many years to come. When it’s first installed, make sure to have it thoroughly inspected before switching it on: key problem areas to look out for include the igniter, fan, exhaust and electrics.
  • Be aware that the outflow pipes on a natural gas tankless water heater will get hot, so be sure to install it somewhere out of the way of curious children and animals. If you have children and they’re old enough, you can also educate them about the risks and dangers involved with the heater.
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