Best Natural Gas Tankless Water Heaters

Tankless water heaters transformed the way we thought about hot water when they first came into our homes several decades ago. While technology has evolved since then, the main principle that makes them highly efficient options have not.

Simply put, gas tankless water heaters are one the most efficient, and cost effective ways to heat your water.

Today we are going to take a look at some of the best natural gas water heaters on the market (in every price bracket). At the end of this article, you will find detailed buyers guide on what to look out for in a good heater (and what to avoid in a bad one). By the end of this (long) article, you should be ready to make the perfect choice for you and your family.

Let’s get started.

Natural Gas Tankless Water Heater Reviews

Gas TanklessGPMBTUWarranty Price
Rinnai RUC98iN Ultra Series 9.8199,000 12-year
Takagi T-KJr2 Indoor6.6140,00010-year
Noritz NRC661 Indoor6.5 120,00010-year
Rheem RTG-64XLN Outdoor6.4 150,00010-year
Marey Gas 10L3.1 79,000 5-year
Eccotemp i12-NG 3.0 80,0002-year

Marey Gas 10L – Best for Small Household

For those of you with a limited budget (and a small household), this heater from Marey provides an affordable option that is of a very reasonable quality. Marey might not have the big name brand recognition that some of the other heaters on this list have, but their products are more than acceptable (by anyone’s standards).

The Pros

For this section, we ask that you set your expectations accordingly. This is a budget heater with a budget price tag. It’s not the biggest, best, or most efficient unit in the world. But it is cheap (which is the biggest plus point this heater has going for it).

For the cost, the 3.1 GPM rating is actually quite impressive. It’s more than enough for a small household that only has one or two people living in it. You can probably shower and use a dishwasher at the same time with this heater, but we wouldn’t recommend you try and use anything more than that.

The energy efficiency rating of this heater is about as good as you could expect from a product in this price bracket. It’s rated .84 to .87 (84% – 87% efficient). It’s not a great rating, but for the price, we feel Marey have done ok.

Installation is super easy, and while we always recommend a professional installation – in reality, anyone with a little experience can get this heater up and running with no problems at all.

The warranty provided is generous (considering the price tag of the unit), although it could be a little longer if we were picky. Marey provides a 5-year warranty on all parts as standard, and this can be extended for an additional cost if you wish.

The Cons

As you might expect from a budget heater, several things could be improved. But, this is a super cheap product (and we need to keep our expectations realistic). For the cost, we have no real issues with this product, but there are a few things that could definitely be improved.

The .84 – .87 energy efficiency rating is our biggest issue with this product. It’s not the end of the world, and there are worse products on the market in this respect. But this rating will make operating costs around 10% more expensive than a higher quality heater.


This is one of those products that is what it is. It’s not particularly easy to use, it’s not very efficient, and its flow rate is reasonably low. But then again, considering the cost of the unit, it’s a bargain. There are much worse products on the market at this price point, and if this is the kind of budget you have – you could do a lot worse than going with the Marey.

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Eccotemp i12-NG Indoor – Best Affordable Tankless Heater

After reviewing the Marey above we couldn’t help ourselves from adding this second budget water heater from Eccotemp as a comparison. On the outside, this looks like a much higher quality product than the Marey (despite being a similar price). But once you get under the hood the two heaters are reasonably similar regarding quality and efficiency.

The Pros

Like the Marey, the main thing that’s going to attract you to the Eccotemp is the price (it’s actually a little bit cheaper than the Marey by around $10 or so). Again this is a budget product, so we need to keep expectations realistic.

The main thing we love about this heater is the usability and ergonomics of the unit. Its sleek black exterior looks very fancy (and expensive) despite it being the cheapest product on our list.

At the bottom of this stunning exterior is an amazingly informative and user-friendly LED display that runs across the entire of the bottom of the unit. The current temperature, GPM, and pressure it’s in real time which allows you to see what’s going on easily. The big easy to use power and temperature buttons are illuminated either side of the display (which makes this basic boiler one of the easiest to use on this list).

The Cons

Unfortunately for the Eccotemp, there are a few things that make it a slightly inferior boiler to the Marey above. The max GPM of both units is reasonably similar, but the Eccotemp is the weaker product with a 3.0 GPM (the Marey has 3.1 GPM).

Again in terms of energy efficiency, the Eccotemp is lagging behind the Marey with a .79 EF rating (79% efficient). This is a reasonably low rating by anyone’s standards. Your energy bills are going to be around 15% higher than some of the more premium and advanced heaters on the market.


This is a beautifully designed and easy to use product. But in real world terms, we think you should avoid this unit and go for the Marey instead. The Eccotemp’s slightly lower GPM rating is almost negligibly worse, but the .79 EF is the deal breaker for us.

Your bills are going to be around 5% – 6% higher with this compared to the Marey. In our opinion, the only benefit you’re getting in return for the additional running costs is a nice looking unit (that’s probably going to be hidden away anyway).

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Takagi T-KJr2 Indoor – Perfect Capability and Affordability

Takagi is a brand that you probably won’t have heard of before (unless you work in the heating industry). However, we know them – and so do many professionals in our line of work. They are a company that has a reputation for no nonsense quality, they skip some of the bells and whistles, but they make great products that do exactly what you would expect of them.

The T-KJr2 is a mid range natural gas heater that in our opinion is the perfect balance between capability and affordability.

The Pros

The main thing you’re going to love about this heater is it’s very respectable 6.6GPM flow rate. There are bigger (more expensive) heaters that have a higher GPM, but in this price bracket, there are not many other products that can really compete with the Takagi.

If you want an idea of what 6.6GPM feels like you can run a shower, your dishwasher, and your washing machine at the same time without noticing the slightest drop in temperature.

Takagi is a company that puts their money where their mouth is when it comes to reliability. They are offering a massive 10-year warranty on the heat exchanger (and a 5-year warranty on all other parts). This is one of the more generous warranties on the market and tells you a thing or two about how much they believe in the quality of their product.

The Cons

While the 6.6 GPM flow rate is very respectable, if you have a large family it might struggle. Two showers being used at the same time (along side a washing machine and a dishwasher) may reduce water temperature. If you think this is a situation that can commonly occur in your household, then you may need to look at investing in a unit that has a higher GPM rating.

The energy efficiency of this heater is also something that we feel is lacking. It’s only rated at .81 – .83 (81% – 83% efficient). There are certainly worse heaters on the market in terms of efficiency (but there are also many better heaters too).


This heater is in it’s great value for money. There are not many other options around this price range that can boast of a 6.6GPM rating. The energy efficiency rating is a little bit disappointing, but it’s not the end of the world. However, we would recommend you consider more efficient (but more expensive) models before making your final choice – over the long run it could end up saving you money.

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Rheem RTG-64XLN Outdoor – Excellent Mid Range Heater

Rheem is one of the big dogs of the water heater world. Their products command respect and admiration from all involved in the industry. The RTG-64XLN is an excellent mid range heater that provides excellent efficiency at a very reasonable price point.

The Pros

There is not much to not to like about this heater. It’s a stunning combination of design, engineering, and materials technology.

One of its unique selling points is its super low 0.26 GPM minimum flow rate. A problem that lower quality heaters have is that there needs to be a minimum amount of water flow before the heater can activate. When you want to wash dishes or use a light stream of hot water, this can cause issues. However, the low activation rate of the Rheem removes this problem almost entirely.

The max GPM rate 0f 6.4 is 0.2 lower than the Takagi above, but in real world terms it’s almost a negligible difference, and the two products can be considered almost equal in this respect. The .82 EF rating again is basically the same as the Takagi and any difference in efficiency between the two models is going to be minuscule.

The Cons

The main issue we have with this heater is that it can only be installed outdoors due to its ventilation design. This could be a benefit in some cases, but drastically reduces the amount of people that can viably use this product.


To be honest, the Takagi and the Rheem are two different products that fulfill two different purposes. One can only be installed indoors, and the other can only be installed outdoors. Apart from that (and the price), these two boilers are exceptionally similar in their performance and reliability. Either of them are great choices that are more than worthy of your consideration.

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Noritz NRC661 Indoor – Best for Most Medium Sized Homes

This offering from Nortiz is technically a premium water heater (in our opinion), but its price is so reasonable that it could easily be considered a mid range heater. However you want to categorize it, there is no getting around the fact that this is a serious product that has some serious performance.

Noritz is somewhat of a legendary company in the heating industry. They were the first company in the world to create an electrically controlled tankless water heater (all the way back in 1981). Ever since then they have continued to innovate and push the boundaries of tankless heating technology and remain one of the big players in the water heater world.

The Pros

This heater is rated at 6.5 GPM which is more than enough for most medium sized homes. You’ll be able to run most your appliances while taking a shower or two with ease.

In the many decades, Noritz has been in business, they have developed a reputation for customer care that other brands can only dream of matching. When you buy one of their products, you can rest assured that they are always going to be there for you if something goes wrong. This heater (like nearly all their other products) comes with a limited lifetime warranty on most of the important parts.

However, the big show stopping feature for us when it comes to this heater is the EF rating. It’s way better than any of the other mid range offerings available with its massive .92 – .93 rating (92% – 93% efficient). This is about as good as heaters can get efficiency wise, it’s a serious achievement that will save you money in the long run.

The Cons

The only downside to this product in our opinion is the price. Considering the performance, we have talked about above we think this product is still great value for money. But if we were picky it could be a little cheaper.


This is a super efficient heater with an amazing GPM rating. However, while it is definitely better than the Takagi, its GPM rating is reasonably similar. It’s a few hundred dollars more expensive but is around 8% more efficient (which amounts to serious savings over the long term).

If this increase in efficiency and performance is worth the additional initial cost – we will leave for you to decide. However, we feel it’s certainly worthy of your consideration.

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Rinnai RUC98iN Ultra Series – The Best GPM Ratings

This heater is the Ferrari of the tankless water heater world. It’s powerful, beautiful, efficient, and expensive. However, if you have the budget for it, we highly doubt you will regret the investment.

The Pros

Where on earth do we start with a heater as good as this!

The 9.8 GPM rating is the biggest and best on this list. In fact, it’s one of the best GPM ratings of any residential natural gas tankless water heater in the world. If you have a large house that uses a large amount of hot water simultaneously, this is the boiler for you. The GPM is so high we feel you would really have to try hard to use more hot water than it can handle.

The efficiency of this heater is off the charts at .96 (96% efficient). To put that in comparison hot water from this unit would 16% cheaper than the hot water from the budget models at the start of this list. When you are using 9.8 GPM of water, that’s not an insignificant saving.

All this power and efficiency is not unheard of, other brands and models in this price bracket can boast of similar statistics. However, many of the other products are giant monstrous water heaters that take up a huge amount of space. The Rinnai, on the other hand, has been painstakingly designed to be as compact as possible. Despite the huge GPM, this product is not much bigger than heaters that have half its capacity.

As the cherry on top to all of this excellence, Rinnai offers a comprehensive 12-year limited warranty on the heat exchanger, a 5-year warranty on the parts, and a 1-year warranty on labor (which can optionally be extended to 5 years).

The Cons

As you might expect, all this performance comes at a cost. There is no getting around it – this is an expensive heater. However, despite the high price tag we genuinely think it’s a bargain considering the efficiency and GPM you are getting. That being said, it wouldn’t hurt for it to be a little more affordable.


If your efficiency or GPM demands are high enough (and you have the budget), this is one of the best heaters in the world. There is nothing we can fault about this product. It represents the cutting edge of natural gas tankless water heater technology. It is more than worthy of your consideration.

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Buyers Guide

Before we dive into some of the slightly technical details in this guide, we thought it would be a good idea to give you a brief overview of how tankless water heaters work.

The concept is reasonably simple in theory, but it took quite a while for the technology to advance enough to make them suitable for widespread usage.

As the name suggests, tankless water heaters don’t store water in a tank (this is the main difference between a tankless water heater and a traditional boiler). This provides several benefits but also has a few consequences too.

The main benefit is that you’re never going to run out of hot water. Traditional boilers that use a tank heat up a batch of water which is then available on demand. But when the water in the tank runs out, tough luck – you’ve gotta wait (or take a cold shower).

On the other hand, tankless heaters don’t need to store water in a tank. The way they heat water is by passing it through a pipe that is surrounded by a series of heating elements. The water comes into the heater cold and leaves hot within a matter of seconds.

This is much more efficient than a traditional storage heater and uses much less energy (as none is lost during the storage process). This also means that they are one of the most eco-friendly ways to heat water in your home.

However, there are limitations to this instant and energy efficient water supply. The main issue is a matter of capacity.

Due to the nature of the way the water is heated up (passing through heating elements), there is an inherent restriction on the amount of water that can be heated up at any one time. The amount varies from a heater to heater, but on average you will struggle to get more than 6.5 gallons of hot water per minute (unless you want to pay over the odds).

6.5 gallons sounds like quite a lot of water, but in reality, can get used up pretty quickly. It’s more than enough capacity to run a few appliances and a shower or two at the same time without any issues. But if you live in a large household you’ll notice you start running out of the water if lots of things that need hot water are being used at the same time.

Electric Vs. Gas

Tankless water heaters come in two main varieties, electric and gas. Both electric and gas heaters have their strengths and weaknesses. Overall natural gas tankless water heaters are seen to be the most user-friendly and efficient.

Purchase Price

In terms of upfront cost, electric water heaters are the clear winner. They are much less complex products to design, develop, and produce. As such they are much cheaper to buy.

Buying Tip: Don’t worry too much about the up front cost of the heater, there are long term factors that are more important economically.

Installation Cost

Again electric tankless water heaters are the winner in this section. Their installation costs are usually much lower than a gas unit. This is because for a natural gas tankless water heater you’re going to need to install proper venting (which is a reasonably large job).

However, installing an electric unit is not exactly a straight forward job either. You need to ensure that your homes current electricity supply are rated high enough to enable operation of a heater. If you had a previous electric heater, this may not be an issue, but in all other cases, you may find yourself needing to upgrade your homes electricity supply.

Buying Tip: If you already have a traditional gas water heater this ventilation is probably already in place. In this instance installation costs are comparable between electric and gas.

Flow Rates

Flow rates are one of the biggest things you should pay attention to when it comes to choosing a water heater. And tankless gas heaters are the undisputed winner here.

As we mentioned earlier the amount of water per minute that can be produced is the biggest weakness of tankless heaters (electric or gas).

“Flow rate” is the name of the metric that is used to indicate how much hot water you can expect per minute.

Buying Tip: When shopping around, get a heater that has the highest flow rate you can afford. It’s the most important factor.

Some of the biggest, best (and most expensive) gas water heaters can provide a massive 9 gallons of water per minute. This is more than enough for most homes to use several hot water sources at once without noticing any kind of drop in temperature.

The best electric tankless water heaters can do around 9 gallons per minute too. However, things are a little more complicated with the electric models. Their flow rate depends on the external temperature.

For example, the 9 gallons per minute electric tankless water heater we mentioned above would only be able to provide around 3 to 4 gallons per minute in the winter months. Colder water takes more time to heat up.

Gas heaters can instantly provide more fuel to keep the heating elements hot, but electric heaters are limited by the amount of electricity they can handle. This means that with electric water heaters the water needs to stay in the pipes longer for it to heat up when cold (which results in a lower flow rate).

Operating Costs

Operating costs are the biggest expense of any water heater. Many people forget this when shopping around and get a cheaper model (but end up paying much more over the long run). This is how they compare:

  • Propane gas water heaters are the most expensive units to run
  • Electric water heaters are cheaper to run than propane gas heaters.
  • Natural gas tankless water heaters are cheaper than both electric and propane gas heaters

Something to bear in mind is that over the next decade or so natural gas prices are set to rise slowly. This may mean that in the future gas and electric heater operating costs could be reasonably similar. Either way, gas heaters are the most energy efficient (and the cheapest to run) at this time.

Efficiency Factor

In our opinion, the efficiency factor is the second most important thing you should be looking out for. This metric represents how energy efficient your water heater is (which in real-world terms means how much it costs to run). Even a small increase in energy efficiency can save you hundreds of dollars over the course of your heaters lifetime.

Efficiency factor (known as EF) is rated on a 0 to 1 scale. 1 (which means 100% efficiency) is the best rating possible (although no brand has ever achieved it).

Buying Tip: The best and most efficient water heaters on the market currently have an EF rating of .92 to .96. Anything in this range is excellent, try to aim for an EF of .90 as an absolute minimum if possible.

User Interface

There is a huge amount of variation between the quality of the user interfaces of different water heaters.

Some of the cheaper and more basic models look like they were designed 30 years ago. They have clunky buttons and obscure settings that require a substantial reading of the instruction manual to understand. They are also much less advanced in terms of intelligence and automatic functionality.

On the other hand, some heaters look like they are something out of a star trek movie. They are sleek, beautiful products that have touch screen displays telling you everything you could ever want to know about your heater in incredible detail. These heaters usually have settings on them that automatically optimise and adjust the amount of energy being used at various times. This can make operating costs slightly lower

Buying Tip: If possible get the friendliest user interface you can find. However, it’s not essential, once you learn how any heater works you’ll be able to operate it just fine. Always go for a unit with the best flow rate and efficiency over usability. But if you need something to help decide a tie breaker between two models with similar specs – consider the interface.


So there you have it, everything you could ever want to know about the best natural gas tankless heaters on the market. We know that this can all seem a little bit confusing if you have never had to deal with water heaters before, but it’s all quite simple really. Just make sure your heater has a large enough flow rate (GPM), and get one that is as efficient as possible to keep your bills down.

All of the products we have listed at the start of this article are winners in their respective price brackets. If you don’t know where to start, we highly recommend you pick one of them. They are more than worthy of your consideration.