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Best Propane and Natural Gas Tankless Water Heaters 2015

Updated on November 10, 2015
With the right tankless water heater at your disposal, you can stop worrying about hot water for the next few decades.
With the right tankless water heater at your disposal, you can stop worrying about hot water for the next few decades.

Provided you choose the right one, a tankless water heater can turn out to be one of the smartest investments you make in your home. Also called on-demand water heaters, these compact units provide hot water for instant use instead of storing it in a tank and letting heat energy drain away. They are inherently more efficient, and that, coupled with their longer average lifetime, can save you the cost of several water heaters over the next decade.

Although electric tankless water heaters are also very popular, because of their versatility and ease of use, many opt for gas units. There is good reason for that: Both propane and natural gas can heat water at only a fraction of the cost of electricity. A high-end gas tankless water heater is probably the most cost-efficient way to supply your home with hot water.

These reviews of propane and natural gas tankless water heaters aim to guide you in your search for the best tankless water heater. First, I discuss the features you should be looking for in a tankless unit. Next, I present a list of the top gas tankless water heater brands and show the pros and cons of their products in an unbiased manner. Once you have gone through the information on this page, you should be ready to decide which on-demand water heater is the most suitable for your needs.

What Features To Look For in a Good Tankless Water Heater

Indoor, outdoor, propane and natural gas versions are available for most tankless water heaters. Needless to say, the first thing you need to decide is whether you want to use natural gas or propane as fuel. Almost always, you will have to upgrade your incoming gas pipe because tankless water heaters have 3/4'' inlets. You should also make up your mind on outside installation vs. indoors installation. Outdoors models are only good for really warm climates while the indoors units are somewhat more complicated to install because they need venting. All the new indoor tankless models I've seen are power direct vent; that is, they are sealed with no contact with the room air. They take combustion air from the outside and dump the fumes with the help of a fan. This is the most advanced and safe venting system when done properly, and allows for horizontal venting.

Let us now have a look at some other key features that make the best tankless water heaters stand out from the rest.

Maximum Flow Rate: This is a measure of how much water is allowed to pass through the water heater at a time in gallons per minute (gpm). For gas tankless water heaters, it varies between about 6 gpm and 10 gpm. Given that an average shower head or faucet has a 2 gpm flow rate, you can easily estimate your required water flow based on the number of water fixtures that will be used simultaneously. The important point is not to confuse this value with the water heater's heating capacity. Sometimes, people come to believe that a 10 gpm water flow capacity translates into 10 gpm of very hot water regardless of incoming water temperatures and other conditions. In fact, although a tankless water heater that is listed as 10 gpm will always give you water at that rate, how hot that water can be depends on the energy input of the unit. That is why, when choosing a natural gas or propane tankless water heater, you need to pay attention to its energy input per hour, that is, BTUs per hour.

Heating Power: One British Thermal Unit (BTU) of energy is equivalent to 1055 joules. Doing some maths, it turns out that approximately 500 BTU/hr is enough to heat water flowing at 1 gpm by 1 °F. Once you know that and the incoming tap water temperatures in your region, it is possible to roughly calculate how many BTUs per hour you require from your prospective tankless water heater. The map can help you find out your tap water temperature.

Note that the water temperatures can vary by season and depending on whether it is ground or surface water.
Note that the water temperatures can vary by season and depending on whether it is ground or surface water.

So, let's say you are in New York, where the tap water temperature is 50 °F, and two people will be showering at the same time while another washes the dishes, and you want hot water at 120 °F. Assuming each outlet takes 2 gpm, and you will be mixing hot with cold water so that you do not scald yourself, we can estimate a hot water flow at 4 gpm. 2,000 BTUs are needed to heat water flowing at 4 gpm by 1 °F; for a 70 °F rise, the requirement is 140,000 BTUs.

You can do your own calculations based on your specific needs and conditions. 120 °F is the maximum temperature you should be seeking, because higher temperatures create a scalding risk. You should also remember that the BTU number in the product spec sheet is not the actual heating capacity. To calculate how many BTUs are actually used to heat the water, you have to apply the energy factor.

Energy Factor: Even the best gas tankless water heater will waste some energy by releasing heat to the outside in its exhaust. Luckily, we have a perfectly objective metric to gauge the efficiency of a water heater, and it's called the energy factor. Energy factor is used for several types of appliances; when we are dealing with water heaters, energy factor means the ratio of the heat energy actually applied to the water to the total energy input delivered to the machine. Let's say a gas water heater has a gas consumption input of 100,000 BTU and an energy factor of 0.8. The actual heating power of this unit is no more than 80,000 BTU, that is power consumption multiplied by the energy factor. With water running through at 2 gpm, this tankless water heater can provide an 80 °F temperature rise. For natural gas and propane tankless water heaters, the energy factor varies between 0.8 and 0.95, depending on whether it is a condensing unit or not.

Condensing Water Heaters: When natural gas or propane is burned to generate heat, the resulting flue gas contains carbon dioxide, nitrogen oxides and water vapor. What concerns us is that this flue gas contains heat energy which is wasted by dumping it out of the exhaust vent. Condensing water heaters address this issue. Without going into technical details, what a condensing water heater does is to use the heat of the flue gas as a secondary heat source, thus saving energy instead of releasing it into the air. The waste gas released from the exhaust vent of a condensing water heater is cooler and in the cooling process the water vapor often condenses back to liquid state, hence the name "condensing".

While non-condensing tankless gas water heaters have an average energy factor of 0.82, condensing water heaters have an energy factor of up to 0.95. Not surprisingly, condensing units cost more. That being said, I advise you without reservation you to choose condensing tankless water heaters. It is not only about saving on fuel. Condensing tankless water heaters are usually the showpieces of the supplier companies and they are likely to put the better components and better workmanship into the production of those. So, in addition to being more efficient, a condensing water heater can have a better build quality.

Build Quality: This is the most important and yet the most elusive feature you want in your prospective water heater. Although gas tankless water heaters usually come with substantial warranties, a malfunctioning water heater is still one of the things you want to avoid in life. Even with the most benevolent customer service, a water heater failure can leave you in a state of deprivation for days and cost you money, time and peace of mind. The best way to avoid such an unpleasant experience is to stay away from products that are blatantly cheap and remember that paying for scrupulous workmanship is the ultimate way to invest your money. In addition, you should check out the customer reviews for the model you are planning to buy to see if there is a pattern of failure with it. Luckily, I have already done the latter for you by sifting through hundreds of user reviews for each brand.

Activation Flow Rate: Finally, a key spec that is often overlooked is the minimum flow rate. Tankless water heaters start heating only when their sensors confirm a certain amount of water is flowing through the system. If the water use remains below that minimum flow rate, the unit will not be activated and you get cold water. Cheap instant water heaters can have activation flow rates as high as 1 gpm and that makes it very easy for you to unintentionally fall below the threshold while adjusting the shower knob and experience a cold water sandwich before you realize you need to increase the flow. Such an interruption can make people furious as it is a waste of time and water. Fortunately, you can sidestep this problem if you simply check out the product specs and make sure you get a unit with a low minimum activation rate.

Having discussed the most important features, let us now move on to see some reviews.

Eccotemp Indoor Tankless Water Heaters

We've got two popular indoor water heaters from the Eccotemp company. They are almost identical, except that FVI-12-LP runs on liquid propane and FVI-12-NG on natural gas. Neither of them are top-quality products, but they get a place on the list because many people install these two, probably because of the low price.

The energy input for both units is 74,500 BTU, which is one of the lowest in the market but acceptable at this price. The energy factor is 0.79, again the lowest, and even lower than what is required by the new federal regulations. That means these two can no longer be manufactured after April 2015, although they can be retailed and installed so they will be around for a while more. Based on the energy input and energy factor, we can estimate that an Eccotemp FVI-12 heats water at a maximum rate of 60,000 BTU/h, which is just enough for one faucet in a cold region and maybe for two in warmer parts. It uses power direct venting, and includes a venting kit, so the initial cost to get the unit installed and running becomes even lower. And the moment it becomes operational is when the problems start.

The first thing you will notice about Eccotemp tankless water heaters is the absence of a clear temperature control. It has two control knobs named "Gas Regulator" and "Water Temperature Regulator," but these two simply allow you to play with the gas and water intake without an option to specify a temperature. Naturally, the temperature will fall when the water use goes up, and it will rise when you use less water. So, be prepared for fluctuations.

The major issue with Eccotemp FVI-12 water heaters is the very high activation flow rate. There is no official data on this, other than a vaguely mentioned 0.93 gpm on the company website. People who use the units suggest it must be at least 1 gpm and could be as high as 1.5 gpm. What we know for sure is that on many occasions a fully open faucet or shower head was not enough to trigger the Eccotemp. In addition, it stops heating all too often for exactly the same reason so it looks like you will have a really hard time to get consistent hot water if you buy one of these.

Finally, Eccotemp gas tankless water heaters could hardly be called reliable as they are among the most poorly rated products in their category. Customer reviews contain all sorts of complaints about the units freezing, leaking and quitting functioning altogether. In fact, Eccotemp's lack of quality even got it involved in a lawsuit. In 2008, a plumbing company bought 75 Eccomtemp tankless water heaters and installed them in clients' homes. 70 percent of the units froze in winter. The plumbing company sued Eccotemp, and the verdict required Eccotemp to pay $750,000 to the plaintiff.

Some people consider Eccotemp water heaters to be a bargain. Indeed, they are if they ever work. This brand is an option if quality is of no relevance to you and you simply need the cheapest, short-term hot water fix. On the other hand, if you want something you can count on, you should probably keep reading.

Navien Condensing Tankless Gas Water Heaters

Navien is a Korean manufacturer that exclusively makes condensing units, and its products are packed with interesting features that you do not see in any other brands. Unfortunately, they are a bit overpriced, and with a surprisingly high percentage of discontented customers, the features hardly justify the cost.

A heavily advertised Navien feature is the stainless steel primary heat exchanger but how that makes Navien tankless water heaters any better than other brands is unclear. All other brands use copper for the primary heat exchanger and stainless steel for the condensing heat exhanger. Copper is suitable for the primary heating unit, because it is a much better conductor of heat and is more resistant to cracking due to extreme temperatures. Stainless steel is corrosion-resistant, so it is good for the condensing part, where the fumes are cooler but acidic. A stainless steel primary heat exchanger could be a liability, not an advantage. Luckily, other features of Navien are of more utility.

Navien water heaters can have energy factors up to 0.99, and for tankless technology, that's impressive. But in absolute terms, that's only a 3 to 5 percent improvement over Rheem or Rinnai condensing water heaters. The savings from such a minuscule difference should not be expected to be more than a few dollars per year; at this rate, it would take a century for energy savings to pay for the price difference between Navien and the other manufacturers.

The high energy factor of Navien is offset by its mediocre flow sensitivity. Navien units need at least 0.5 gpm water going through to keep the heating process going, and that’s not nearly as good as Rheem condensing tankless units that cost no more than two-thirds of Navien's. Probably to address this weakness, Navien has developed a built-in recirculation tank feature.

Navien NR-A and NPE-A series heaters are equipped with a buffer tank that keeps 0.5 gallons of water hot all the time. This allows you to bypass the minimum-flow-rate obstacle and get hot water faster at the faucet. The tank is reported to be poorly insulated, which sort of defeats the purpose of going tankless, but it seems to work because customers rate the Navien models that have buffer tanks higher than the Navien models that don't. The NR-A and NPE-A series also have built-in hot water recirculating pumps. This device sends the cooling water in the hot water pipes back to the water heater so that there is always hot water in the pipes, ready for instant use. That helps save time and water, and a recirculation pump that works with a tankless water heater can cost a few hundred dollars. I am not sure about the reliability of a built-in hot water recirculating pump, but it explains the high price to some extent. A Navien NPE-240A condensing water heater would be no bad choice, had it not been for the widespread quality issues that plague Navien products.

Indeed, the charm of the high-tech features disappears once you start reading the customer reviews. Rated very poorly by customers, Navien units are reported to frequently run into problems that range from failure of circuit boards to malfunctioning flow detectors and even leaks. I am sure some of these incidents are caused by people who fail to take care of their water heaters and blame it on the manufacturer, but the consistent poor reviews on nearly every Navien product tells us that something is wrong with Navien. The Navien customer service is reportedly willing to help and sends replacement parts without much hassle, but that does little to help the inconvenience of having no hot water for days and paying a plumber to diagnose the unit’s problem. Such things happen too often to be acceptable for such an expensive appliance. You should also note that Navien recalled 13,000 units in late 2011 due to a risk of carbon monoxide poisoning.

Given the poor user experience, I feel a bit sorry that I cannot recommend Navien, as its products do have some promising features. If the durability issues are fixed in future products, Navien could one day be named the best tankless water heater—but that day is not today.

Takagi Tankless Water Heaters

Originally a Japanese manufacturer, Takagi was one of the first to introduce tankless water heaters to the United States market. Takagi handed over its marketing operations in North America to A.O. Smith in 2011, months after Rinnai withdrew from a tankless venture with the latter. A.O. Smith is a well-known American manufacturer of tank-type hot water heaters although it is a latecomer in the tankless market.

Takagi has a wide selection of tankless models and it is possible to know most specs of a Takagi unit by looking at the product name. T-H3 series are the condensing water heaters. T-D2, T-K4 and T-KJr2 refer to the large, mid-size and small non-condensing units respectively. OS means outdoors and IN is indoors. Letters N and P at the end of the model name tell us whether it is natural gas or propane.

Most Takagi water heaters range between 140.000 and 200,000 BTUs, although heavy duty ones up to 380,000 BTUs are also available apparently for commercial applications. Condensing models have energy factors that range between 0.93 and 0.95 and for the non-condensing, energy factor is 0.82. In other words, Takagi tankless water heaters are as efficient as any other gas tankless water heater.

Takagi's weakness is the minimum activation flow rate. Regardless of size, all Takagi models have a threshold of 0.5 gpm to start heating the water and a minimum flow of 0.4 gpm to keep running. This is not as good as Rheem or Rinnai tankless water heaters, and with a Takagi unit, you are more likely to turn down the heater by mistake and temporarily get cold water. I am not surprised that Takagi is not very eager to make this known. The only way to find out is to dig deep into the manuals. By its evasiveness, Takagi kind of admits the minimum flow rates are not that good.

As for what the users feel about Takagi, it looks like they are usually happy, but there are also a few complaints about the overall reliability of the units. The interesting point is that people who have been familiar with Takagi water heaters for a decade or so claim that Takagi quality is not what it was before the joint venture deal with A.O. Smith. Others who have had the chance to compare Rheem with Takagi suggest that Rheem gas tankless water heaters are actually more reliable.

On the whole, no one can say that Takagi is not a decent brand of tankless water heaters, and the chances are you will end up quite satisfied with a Takagi unit. Yet, the occasional bad customer reviews, coupled with product specs that are far from exceptional, gives the impression that you will be paying more for the brand name than tangible features and quality, and that's after the brand name has been bought by a company that is not so much into the tankless concept. I humbly suggest that you take a look at the Rheem tankless units before you make a final decision.

Rheem Indoor and Outdoor Gas Tankless Water Heaters

There is this assumption about tankless water heaters: that they are a Japanese thing, and that you have to get a Japanese brand if you want them to work. Well, in recent years, Rheem has come up with top-notch natural gas and propane tankless units that are also well-priced, belying the notion that American brands can't handle the tankless technology.

There are two series of gas tankless water heaters from Rheem: the Prestige™ or RTGH series, which are condensing and much more efficient, and the more affordable Mid-Efficiency or RTG series. The models vary between 150,000 BTU to 200,000 BTU, with maximum flow rates of 6.4 to 9.5 gpm. That means even the smallest Rheem should be able to supply plenty of hot water for an average household; but if you are not frugal when it comes to showering, you might want to do your own calculation and get one of the sizier Rheem units. As for efficiency, the non-condensing RTG series heaters have an energy factor of 0.82, and the condensing RTHG heaters an energy factor between 0.92 and 0.94, which is the standard efficiency of gas tankless units.

The feature that actually makes Rheem gas tankless water heaters differ from the ones we've seen so far is the very low minimum flow rate. Water flowing at just 0.4 gpm is enough to activate a Rheem tankless water heater, and once it is activated, you can go down to 0.26 gpm and still get hot water without the heater shutting down. Given that no water outlet has a lower than 2 gpm flow rate, you will probably never have to go through unintended intervals of cold water with a Rheem, which will add much to your comfort and savings. Only Rinnai, which is deemed the best gas tankless water heater manufacturer has similar minimum flow rates but Rheem simply offers it at a better price.

The customer reviews for Rheem units are very good, with next to zero complaints. The consensus of users is that Rheem gas tankless water heaters are well-priced, easy to install and reliable.

Another thing I really like about Rheem is the built-in condensate neutralizer in condensing models. All condensing tankless water heaters have a condensate drain pipe that comes out of the bottom of the unit; condensate water from this pipe has a degree of acidity equal to that of lemon juice or vinegar. Releasing this liquid into your drainage system without diluting or neutralizing it could corrode the drain pipes over the years. Sometimes, the local building codes require you to install a condensate neutralizer. Although, I don't know of any incident where someone's drain system was eaten away by acid from a condensing water heater, having a condensate neutralizer is always better than having none. This accessory can cost from $50 to $100, so a built-in neutralizer is a nice extra that cuts installation cost and time.

When selecting a Rheem gas tankless water heater, you can find out the key product specs by simply checking out the model name. The number on the model name refers to the maximum flow rate. X means exterior, i.e. outdoors, and DV means direct vent, i.e. indoors. The letters N and P at the end of the model name tell whether it is natural gas or propane. So the Rheem RTGH-95DVLP is a condensing indoors natural-gas unit with 9.5 gpm flow rate capacity, and the RTG-64XLP is a non-condensing, outdoors, propane tankless water heater and has a flow rate of 6.4 gpm. Note that the newest versions of each Rheem model has an L in its name, so RTG-64XP is basically an older version of RTG-64XLP (needless to say, you want the newer one).

All in all, Rheem seems to have put in the work to develop some top-quality natural gas and propane tankless water heaters that just do the job without a fuss. User experience is positive, and with the price being right, I can recommend Rheem units without reservation. In fact, one of the condensing Rheem RTGH Prestige units would probably be my choice, if I needed a new water heater right now.

Rinnai Tankless Water Heaters

Rinnai tankless water heaters have similar specs to Rheem's, and slighly higher prices. Yet, Rinnai remains the leader of the tankless market, simply because it has established itself as the most trusted manufacturer with solid products that are built to the highest quality standards in the world.

The Rinnai RU (Ultra) series are condensing tankless water heaters with energy factors up to 0.96, making them more efficient than most other brands. Their energy inputs range between 150,000 and 200,000. The V (Value) and RL (Luxury) series are non-condensing and their energy factor is the usual 0.82. The V and RL series have basically identical features. The RL series varies between 200,000 BTU and 180,000 BTU, whereas the V units offer smaller and more affordable options ranging from 180,000 BTU to 120,000 BTU. Like most other brands, you can find out the key product specs simply from the model name. The numbers on the product names tell the maximum flow rate while I, E, N and P refer to indoors, outdoors, natural gas and propane. It is no big deal to guess that RU98IN, one of the top Rinnai models, is a condensing indoors natural-gas unit with a 9.8 flow rate limit.

All Rinnai units switch on once a water flow of 0.4 gpm is achieved, and they keep running as long as the flow stays above 0.26 gpm. With such low activation flow rates, Rinnai units are basically the most sensitive tankless water heaters in the market, together with Rheem.

The Rinnai Ultra and Luxury series have a special feature called Circ-LogicTM. This is a built-in computer program that can control the operation of an external hot water recirculation pump, definitely something handy if you plan to install a recirculation system.

Rinnai makes state-of-the-art on-demand water heaters, and more important, its unmatched reputation as the most reliable manufacturer makes it the number-one selling tankless water heater in US. Made in Japan, Rinnai is by default the acme of tankless technology. Not surprisingly, the majority of the customer reviews laud Rinnai's quality and reliability; the few complaints often come from people who did not pay enough attention to the installation and maintenance of the unit.

The only legitimate issue with Rinnai seems to be the reportedly cumbersome customer support process. For the warranty to remain valid, the unit must be installed and repaired by a Rinnai certified contractor and that makes things a bit more costly and slow, and can cause some frustration if your unit ever fails.

In conclusion, there is a near concensus that Rinnai is the best tankless water heater manufacturer and I humbly agree. While I feel that Rheem would be the optimum choice because of the more competitive pricing and hassle-free customer service, I also have no doubt that a properly installed and serviced Rinnai will give you nothing less than the ultimate tankless water heater experience.

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    • profile image

      Cezary 23 months ago

      We have tried both a tankless propane water heater from Takagi, and an

      electric one from Stiebel Eltron. The minimum turn on flow was a problem with both. Our water is pretty hard, and has a high iron content. It requires a lot of processing to be usable in such heaters. The Takagi lasted about a year. We started using a polyphosphate cartridge since we got the Stiebel, which lasted perhaps 3 years - it just went bad.

    • profile image

      Max 20 months ago

      What is the best tankless unit with a PVC exhaust? Also where does BOSCH Tankless heaters fit into this editorial or is this a Rheem & Rinnai promoting site?

    • profile image

      David Davis 16 months ago

      I never thought of putting more than one water heater in my house. I want to get a tankless water heater, but I wasn't sure if it would work for our house. We generally aren't trying to run laundry, dishes, and showering all at once anyways. Putting in two units could definitely help, maybe just one for each floor. Thank you for giving this explicit reviews, I'll be checking on the Rheem's some time now.

    • profile image

      Steve Sauerbry 16 months ago

      I am switching from electric water heaters at my cabin in Northern Minnesota to a tankless system. The builder mentioned a Bosche- Has anyone heard of these.

    • profile image

      Daviddavis2525 16 months ago

      Thank you for this great review of last years water heaters. I've been through a lot of sites like the tanklesswaterwonder.com and others, but i didn't get this kind of review. I'll be making sure to keep this thought in mind while I buy my gas water heater for the house we have today.

    • roob profile image

      Ruby 14 months ago from USA

      Being a plumber, I would say avoid Rheem, it is a home depot brand and home depot plumbing products are not good!! Go with the navien, it is the best unit mentioned! Circ pump inside & it is a smart machine. It's a little big but it will fit your needs and more!

    • profile image

      Diana 13 months ago

      I'm looking for reviews on a Noritz tankless propane water heater. Please help me know if this is a good product.

    • Linda Robinson60 profile image

      Linda Robinson 12 months ago from Cicero, New York

      Hello Toasty so nice meeting you. This is an outstanding so well informed hub for anyone considering purchasing a propane or natural gas tankless water heater. You left nothing uncovered. An excellent source of information to have the average person made an intelligent decision. An super hub and definite must read. :)

    • profile image

      Bill S. 12 months ago

      Great comprehensive article. I was wondering if you have had any experience with the Laars Marscot FT?

    • profile image

      Fred Baker 11 months ago

      Very helpful review. We live off grid in southern Arizona, currently using a 50 gallon A.O. Smith hot water tank because when I first "upgraded" our homestead to include hot water a few years ago, the solar hot water heater made tankless heaters unworkable. At least at that time, data on them stated that the tankless units simply would not come on if "warm" water was coming in through them. But last year the solar tank was taken out of the plumbing loop, so tankless might now be an option.

      One thing I do not understand about this review is the lack of comment moderation by the author. Previous commenters have raised some good questions; it would have been nice to see a balanced discussion.

    • profile image

      MB 7 months ago

      Is there any way I can consult with the author of this valuable review article? I am a decades long tankless hot water heater user (Paloma) and would like to reference the Rheem unit that will best fit my use needs. I see others have posted questions; how does the response process work?

    • roob profile image

      Ruby 7 months ago from USA

      @MB I would steer clear of Rheem as that is just a home depot brand... yuck. I would go for a Noritz or Renai which can be found at Ferguson if you are purchasing yourself. I was a plumber & still work for a plumbing company. Ferguson's employees are also more knowledgeable than Home Depot, don't be intimidated by the mostly contractor shoppers, they will still help out the home owner!

    • profile image

      KevinH 2 weeks ago

      Why not just use the dehumidifier that I have in the basement anyway, to get FREE hot water?

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