Tankless Water Heater Guide 2018

Find the best tankless water heater for your home with our ultimate buyer’s guide and top 10 tankless water heater reviews. We’ve got everything you need to know right here.


Let us help you find the perfect tankless heater for your home.

We’ve included all the key facts about the top models in the table below. Following the table we review each in a bit more detail.

These are the top rated water heaters available. They come in a range of price brackets, but all have great reputations. We’ve included both the top electric tankless water heater reviews and the best gas powered models too.

Check out our buyer’s guide to see what key features you should be looking for in a tankless water heater.

We’ll start with the comparison table and reviews. Alternatively, jump to the Introduction to Heaters & Buyer’s Guide

Stiebel Eltron Tempra 24 Plus

4.7$$$5.4ElectricReliable, great temperature controls, consistent hot water flowThree year warranty is less than other models
Rinnai RUC98iN Ultra Series

4.6$$$$$9.8GasHigh energy efficiency rating, huge water flow rate, 12 year warranty on heat exchangerMore expensive than most

Takagi T-KJr2-IN-NG

4.6$$$6.6GasHigh water flow rate, turns itself off if overheating, 10 year warranty on heat exchangerVenting required


4.3$$$$$9.5GasHigh energy efficiency, quality components, massive flow rateOne of the more expensive tankless system we've reviewed
EcoSmart ECO 27

4.3$$6.0ElectricWorks well in colder climates, energy efficient, digital controls, limited lifetime warrantyWater flow rate lower than some competitors

Rinnai RL75iN4.3$$$$$7.5GasOffers a large temperature range, can be converted from gas to propaneMust use the listed vent

EcoSmart ECO 114.1$2.0ElectricDigital controller gives complete control, limited lifetime warrantyOnly suitable for smaller homes
Eccotemp L10

4.0$2.65GasAuto shut-off, portable, great priceLimited flow rate, only suitable for small homes & RVs

Eccotemp FVI-12-LP

3.9$$3.4GasLow energy consumption, perfect for smaller homesWouldn't suit homes with more than one bathroom

Rheem RTE 13

3.7$4.0ElectricGreat value, reliableNo digital display

GPM stands for gallons per minute. This is a measure of how much hot water can be provided every minute. Larger families will need larger numbers.

Next, you can read our more detailed tankless hot water heater reviews. We give our recommendations for the best gas tankless water heater systems and the best tankless electric water heaters.

Stiebel Eltron Tempra 24 Plus Electric         BEST ELECTRIC WATER HEATER – OUR PICK

The Stiebel Eltron Tempra is an electric tankless water heater that comes with really impressive customer feedback. It is considered one of the most technologically advanced systems on the market today. It features Advanced Flow Control (a feature exclusive to this heater) which ensures that there is always a constant flow of hot water, no matter how big the household water demands are. This model doesn’t have the problem with temperature fluctuations like some others do.

The Tempra features a maximum water flow rate of 5.4 gallons per minute (GPM). This makes it able to handle the hot water needs of medium to large households. It can handle the demands of homes with two bathrooms. The temperature is controlled accurately with the help of a digital temperature control. This means you can be very precise (down to the degree), and not waste any energy heating the water to unnecessarily high temperatures. It’s German engineered, and just like their cars, it’s a great piece of design.

The Tempra has been given a recent redesign to improve on an already impressive machine. The new improvements include:

  • Upgraded electronics
  • Flow sensor design
  • Hinged cover (for easy access)
  • Advanced Flow Control system

Since it is an electric heater it doesn’t require any outside venting. This makes installation much easier than a gas model. You must make sure that you have the power capabilities at home to handle a water heater though.

It features a slim, sleek design and will take up very little space. It measures 16 5/8 (width), 14 ½ (height), 4 5/8 (depth). If you are moving from a traditional tank based water heater to this, then you are definitely going to have some extra space at home to fill.

Stiebel estimate that you can save between 15-20% on your hot water bill each month compared to a conventional hot water heater.

Bottom Line: This heater has combines some amazing technology and reliability into a tempting sleek unit. It’s a system of really high quality, and a recent price drop makes it amazing value on Amazon now too. This is one of the best electric tankless water heaters out there.

Key Features:

  • Rating: 4.7
  • Price: $$$
  • Electric tankless water heater rated for 240 V @ 24 kW
  • 5.4 gallons per minute water flow
  • 3 Year warranty
  • Advanced Flow Control technology
  • Digital temperature controls
  • Slim line design
  • Robust and dependable


This model from Rinnai is a gas powered heater. It features the highest energy efficiency rating we have seen. It has a thermal efficiency of 95% and an Energy Star certificate. It also has an Energy Factor rating of up to 0.96. This is among the highest ratings available in a home water heater. This means it is able to run more efficiently than most heaters, saving energy and money in the process.

This model has an expensive initial cost, but you can expect energy bills to fall due to its efficient operation. It also has a staggering max water flow rate of 9.8 GPM. This means it is able to service even the largest of households. Even homes with 4 or 5 bathrooms won’t have any problems with this model. In fact, Rinnai say it is able to handle 4 showers running simultaneously. This water heater will never be in any danger of a drop in pressure. Even when running at full capacity, it will do so quietly. This is said to be one of the quietest tankless water heaters on the market.

As it is a gas powered system is does require outdoor venting. Rinnai is the only manufacturer to offer two venting options on installation. The unit ships with both concentric and twin pipe PVC venting included. This gives more freedom at installation time.

Being one of the more expensive models, it also comes with a solid warranty. You get 12 years on the heat exchanger and 5 years on the parts. Aside from the EcoSmart models, this is the best warranty we have seen.

Bottom Line: Though initially more expensive, this model will save you more in the long run due to its exceptionally efficient operation. This model tops our tankless gas water heater reviews, and is a system of real quality. Rinnai is probably the best water heater brand in the business.

 Key Features:

  • Rating: 4.6
  • Price: $$$$$
  • Energy Star certificate
  • Amazing energy efficiency
  • 9.6 gallons per minute water flow rate
  • Min/max BTUs: 15,200-199,000
  • Really low NOx emissions
  • Warranty: 5 years parts, 12 years heat exchanger

Takagi T-KJr2-IN-NG Gas             GREAT EFFICIENCY & VALUE

Despite having one of the most unimaginative names in the whole house tankless water heater world, the Takagi T-KJr2-IN-NG is actually a heater of some pedigree. It is attractively priced for a unit that packs so many impressive features.

It is a gas water heater. This means that is slightly more efficient than an electric unit, but it will require external venting to allow the gases to escape. The unit needs 4 inch category III stainless steel venting.

It comes with an Energy Star certificate. This means it has been recognized as being one of the more energy efficient models on the market. It boasts an energy factor of 0.81-0.83. Now this isn’t quite as efficient as the Rinnai model we just talked about, but be aware that this unit from Takagi costs less than 1/2 of the price. It packs quite a punch for something so well priced.

An impressive feature of this water heater is its ability to monitor the input and output water temperatures to maintain a steady temperature. This means there are no temperature fluctuations when you are having that relaxing shower.

This model from Takagi gives an impressive water flow rate of 6.6 gallons per minute. This makes it suitable for even large homes. Homes with 2 bathrooms can be supplied with enough water for two showers to run simultaneously quite easily.

Bottom Line: This is impressively priced for something with Energy Star certification. A great option that doesn’t have to break the bank. It’s got most of the perks of the more expensive units, but lacks the price tag. This tankless hot water heater reviews really well.

Key Features:

  • Rating: 4.6
  • Price: $$$
  • Gas powered tankless water heater
  • 6.6 gallons per minute maximum water flow rate
  • Energy Star certificate
  • Great value
  • Warranty: 5 years on parts, 10 years on heat exchanger
  • 140,000 BTU

EcoSmart ECO 27 Electric                TOP BUDGET CHOICE

The ECO 27 is our budget choice, but don’t be deceived into thinking that this isn’t an impressive water heater, because it is. It’s attractively priced and boasts an array of impressive features that should make it a worthy consideration for any prospective buyer.

An awesome feature of this heater is its ability to function even in the colder of climates. Tankless water heaters don’t like really cold water, but this model will work with water as cold as 37°F. Now you won’t reach the peak performance level of 6 gallons of water a minute at this temperature, but it will cope better than others. EcoSmart say that the peak water flow rate of 6 GPM is capable of handling the hot water demands of 4 showers running simultaneously.

It features a digital temperature control which allows you to adjust the heat to the nearest degree. By controlling the temperature so precisely you can save energy, and adjust the settings according to the time of the year. The temperature can be adjusted between 80°F – 140°F. This is one of the least expensive models to offer digital controls like this. Another great feature is its advanced self modulating technology. This lets the ECO 27 adjust how much energy is needed according to how much hot water is needed.

For me the most amazing thing about this model is the lifetime warranty. This is unique in the heaters that I have reviewed and is made even more impressive a fact when you consider the price of the unit. This is the best electric tankless water heater when it comes to value for money.

The unit is slim and attractive. It measures just 17x 17x 3.8 inches. It is made up of high quality copper and stainless steel components that are durable, efficient, and easily replaced.

Bottom Line: Our budget choice due to the array of features and amazing warranty it offers. If you live in a colder part of the country, then this whole house tankless water heater is definitely worth a close look. This whole house electric tankless water heater reviews really well on websites like Amazon too. Due to the outstanding value it offers, this is one of the best hot water heaters available.

Key Features:

  • Rating: 4.3
  • Price: $$
  • Electric powered tankless water heater
  • Rated for 240V and 27kW
  • 6 gallons per minute maximum water flow rate
  • Will operate in colder climates
  • Digital temperature controls
  • Advanced self modulating technology
  • Lifetime Warranty


This comes out on top in our gas tankless water heater reviews. It’s one of the more expensive models we’ve encountered, but it backs up the price tag with some impressive stats. It packs a whopping 94% energy efficiency! If you are serious about reducing energy bills, and also your impact on the environment, then this is water heater isn’t one to be missed.

Besides high efficiency it also offers a large capacity. It will happily output up to 9.5 GPM of hot water in your home. This is among the largest capacities available in a domestic heater of this type. It is more than capable of looking after the hot water demands of a really big family home with multiple bathrooms.

It features electronic controls and a digital display that allow complete control over the settings. It is even able to self diagnose any issues, which makes maintenance really simple and straightforward. The electronics are designed to increase energy efficiency and safety. The individual components are tested by third parties to ensure the highest of build qualities.

This Rheem heater has an exclusive water savings setting. This is designed to save up to 1,100 gallons of water per year by reducing the flow of water until the temperature reaches the threshold set on the unit.

Another awesome feature is the introduction of a minimum water flow rate and activation point. This means the home will receive hot water even in times of low demand. Some tankless heater struggle to output enough hot water unless the water demand reaches a certain level. No such problems with this model.

As it runs on gas it requires external venting. It can accommodate up to 38 feet of 3 inch pipe or up to 5 feet of 2 inch PVC pipe. The unit is designed too emit lower levels of NOx.

Bottom Line: Hard to match on efficiency and features. It doesn’t come cheap, but you can be assured of its quality and efficiency. This tankless gas water heater reviews really well from anyone that uses it.

Key Features:

  • Rating: 4.3
  • Price: $$$$$
  • Gas powered tankless water heater
  • 9.5 gallons per minute water flow rate
  • Smart electronics
  • Up to 94% system efficiency
  • Digital controls
  • Hot water even in low demand situations
  • 5 Year warranty


Rheem RTE 13 Electric               AMAZING VALUE

This Rheem tankless water heater reviews really well, and it is also the cheapest we have featured. It is the most popular hot water heater on Amazon, and has hundreds of favorable reviews. It is electrically operated and fits standard 1/2 inch fittings.

A max water flow rate of 4 GPM isn’t huge, but it can easily handle small to medium homes.  It doesn’t have the delicate digital controls of other models, but comes at a fraction of the price. This is a unit that is unspectacular in its design, but has shown to be a consistent and reliable performer, time and time again. It comes highly recommended on Amazon by many happy customers.

Bottom Line: This model is cheap (relatively speaking) and it doesn’t show off. It’s a dependable water heater, that is a perfect for medium to small homes, and even holiday homes.

Rinnai RL75iN Gas               TRUSTED PERFORMER

This is the second of the Rinnai tankless water heater reviews we have featured. The RL75iN is a gas operated system that is suitable for homes with 2-3 bedrooms. It offers a max water flow rate of 7.5 GPM, which is quite substantial.

It comes with a really good 12 year warranty on the heat exchanger (5 years on parts). It is Energy Star certified which means it offers really good energy efficiency.

It is controlled digitally so the user can have complete control over temperature settings to the nearest degree. This has the benefit of saving energy, as you can be very precise with how hot you need your water. Being a gas system it will require ventilation. This Rinnai tankless water heater has a great reputation, and the brand is held in high regard.

Bottom Line: A trusted brand that offer exceptional performance. An Energy Star certificate proves how capable it is of efficiently heating water in the home.

Eccotemp FVI-12-LP             GREAT VALUE

This model runs on propane which is a more efficient power source than the electric powered models.. It has a digital display system, and has independent controls for water and gas. It has a maximum water flow rate of 3.4 GPM which would suit smaller homes best.

The 2 year warranty is a bit less than what competitors are offering, but this system is one of the cheaper water heaters available. It doesn’t consume as much energy as other models, but doesn’t heat water to such a high temperature.

Bottom Line: This is a great choice for smaller homes. It doesn’t use as much gas as other units, and does a great job in the right circumstances.

Eccotemp L10 Outdoor               RV Tankless Water Heater

This water heater is slightly different to the others. It is portable and can be installed outdoors. Due to its smaller size, it also has a lower water flow rate of 2.65 GPM. It comes with standard 1/2 inch fittings so can be installed easily. It also has an automatic safety shut-off to prevent accidents.

This Eccotemp model is competitively priced, and is one of the cheaper units we have looked at. It’s a great fit for RVs, vacation homes, and campers. It wouldn’t be able to be heavily used, but would work well under the right circumstances.

Bottom Line: The perfect RV tankless water heater. It’s well designed for the demands of traveling.

EcoSmart ECO11 Electric               BEST FOR COLD CLIMATES

This whole house electric tankless water heater from EcoSmart has an intuitive digital interface, giving the user complete control over hot water operations. Being from EcoSmart it also has the advantage of having a lifetime warranty. This is an amazing feature, which makes EcoSmart models unique.

This model is suited for smaller homes, and has a relatively low water output rate of 2 GPM. If you have more than one bathroom then, you should take a look at the larger EcoSmart ECO 27 which we discussed a bit further up the page. Likewise, if you live in a place with a colder climate, the ECO 27 would be a good fit. In smaller homes, this heater can do a really efficient job. It has an attractive price tag too.

Bottom Line: This is one of the few heaters that will work well with colder input water. A lifetime warranty isn’t to be taken lightly either.

Tankless Water Heater Buyer’s Guide

Tankless or ‘on-demand’ water heaters are a more energy efficient solution to the problems posed by old fashioned storage tank heaters. The water heaters of the past were ideal in their day, but in modern times we need a more practical solution.

Rather than store heated water in a giant tank, tankless heaters heat the water as and when you need it. This ‘on demand’ function makes them more energy efficient, and means you can save money on your energy bills each month.

One of main categories you will see mentioned about these units is the maximum water flow rate. This number should be one of your key considerations when browsing on-demand heaters. Measured in gallons per minute (GPM), this is the amount of hot water that will be available to your household at a particular time. The top models will give as much as 10 GPM, which will be enough for even the biggest of families. Anyway, more of that later…

Tankless water heaters were first readily available around 10 years ago. However, in their infancy they were unreliable as technology wasn’t quite ready for them. These days technology has turned them into machines of efficiency and they have improved in every area.

Improvements in Modern Day Tankless Water Heaters

  • Modern day water heaters retail at much less intimidating prices than those of 10 years ago.
  • They are easier to install, as they have more practical designs which makes connecting to existing gas lines much more straight forward.
  • There are no longer problems with inconsistent water temperatures. Manufacturers have solved this problem in innovative ways by introducing buffer tanks and recirculation pumps.
  • They are more reliable and much easier to maintain.

How Do They Work?

Gas and electric tankless water heaters work in the same way as standard water heaters that have tanks. The difference is that they are able to heat the water much more quickly, and are able to work only when needed. This means they don’t need a storage tank, and don’t use up the energy needed during standby operation.

When a hot water tap or appliance that draws hot water is turned on in the home, cold water is drawn into the water heater. The unit senses the flow of water and activates the burner. This in turn warms the heat exchanger (the part that heats the water). The heat exchanger is surrounded by the incoming cold water, which is then heated to the desired temperature, ready to travel on to the desired location. Since these units only heat water as it is required, they are much more efficient than conventional water heaters.

Some Energy Star certified tankless hot water heaters use a further heat exchanger. This allows them to use 9 % less energy than regular units. The second exchanger takes heat from the combustion gas, and condenses (cools) it. This means that the exhausted gas is much cooler than regular systems. Generally speaking, if the exhaust gases are cooler then it means the system has been more efficient and less energy has been wasted.

Before You Buy: Checklist

1. Estimate the capacity that you’ll need.

This is really important with a tankless system. If you choose a model that can’t keep up with demand, then you won’t get any hot water.

While capacities of storage water heaters are defined as the number of gallons that fit into the tank, whole house tankless water heaters are measured in a different way. So how is the capacity of a water heater measured? Well, tankless hot water heaters are defined by the amount of hot water they produce in one minute. This gallons per minute (GPM) rating can vary from about 2-13 through different manufacturers. To estimate the type of capacity that you will need, you should imagine peak water usage times in the home. Here are some average numbers to help you estimate your peak water usage:

Reason For UseGallons per Minute (GPM)
Clothes Washer3.3
Shower and Bathtub2.5
Kitchen and Bathroom Sink2.2

If for example, you have two bathrooms and there are times when people will be showering simultaneously, then a model with a GPM rating of at least 4 would be desirable. However, a one bedroom home could suffice with something as low as 3 GPM. These GPM ratings also depend on the temperature of the incoming water. If you live in a cold area then expect the stated GPM value to be lower.

This isn’t the only number that you should be checking though. Each model has its own sizing chart. This includes information about the flow rate, the number of hot water fixtures in a home, and the effect of temperature rise. The sizing chart displays how a water heater performs in each situation, so that you can make sure you get the right sized model for your home.

Check out the sizing chart for the Stiebel Eltron Tempra range here.

2. Check out the warranty. 

The longer warranty models will probably be more expensive, but for something that is going to get used as much as this, it might well be worth it. Warranties can run for over 10 years with some models. Be aware that most of the warranties depend on the unit being installed by a professional. The best tankless water heaters come with solid warranties.

3. Think about where you will install it. 

The units themselves are very small and compact. However, some will need to be installed near a gas supply, and some models will need ventilation for combustion gases. Changing to a tankless system from one that uses a tank will free up some valuable space anyway.

4. Make sure your home is a good fit for a tankless heater.

If your current water heater is electric and you don’t have the capability to provide propane or gas, then you probably shouldn’t go for a tankless system. You would need to increase the capacity of your electrical system by too much for it to be worthwhile.

Also, these types of heater don’t fit extremely cold water supplies. The heater’s capacity depends on the incoming water temperature. The colder your water the less GPM of hot water you will get. This is because it has to heat the water more and for longer because its cold. Choose your tankless water heater based on the winter water temperature in your area. This caters for the worst case scenario. The output will be much better through the other three seasons.

Why Get A Tankless Water Heater Instead of A Regular One?

They have many benefits over standard water heaters. Let’s have a look at why they are a better fit for your home.

  • They are more energy efficient. They only heat water when it is needed.
    • Water heaters are said to account for around 25% of all energy consumed in a household. Improving the energy efficiency of this unit will make a big difference to consumption.
  • They are cheaper to run because of this.
  • They won’t run out of water. A standard water heater only has as much hot water as is inside the tank.
  • They take up less space. A residential tankless heater is only around the size of a small suitcase.

Tankless Water Heater Pros and Cons


  1. More energy efficient – As these systems don’t have to maintain the water at a constant temperature, they use less energy. They work on an ‘on-demand’ basis. This means they use just the right amount of energy to heat the amount of water that is needed. Energy is not wasted keeping a tank hot. They also provide a more consistent temperature of water, meaning that scolding hot water doesn’t come out of the faucet. This again saves energy. The best tankless hot water heaters are incredibly efficient machines.
  2. Cheaper to run – A by product of being more energy efficient is that they will save you money on your energy bills too. Water heaters can account for around 25% of energy bills, so significant monthly savings can be made.
  3. Space saving – Traditional water heaters with tanks can be huge. These units don’t have a tank so require very little space. Even the larger units are only around the size of a medium suitcase.
  4. Won’t run out of hot water – These units heat the water as and when it is needed. This means they are not limited by the size of a hot water tank. As long as you have a model that has a water flow rate big enough to keep up with demand, then you won’t run out of hot water.


  1. Not great in cold weather – If your incoming water is likely to get seriously cold, then maybe a tankless system isn’t a good fit. This would require a lot of energy to get the water hot and would slow down the water flow rate. You could get around this problem by getting a system with a really large flow rate.
  2. Start-up cost – These system are generally more expensive than their traditional counterparts. They may also require some extra work upon installation, if you need to upgrade existing gas or electrical infrastructure. In the long run you are likely to save money and you will recoup this cost.
  3. Not a good fit for really large households – I’m talking +4 bathrooms in size. This would push the limits of the high capacity systems, and might even need multiple systems to cope.

How Do I Maintain a Tankless Water Heater?

These devices contain a heating exchanger (heating coil) which is surrounded by water when it is in operation. Water contains minerals like calcium and magnesium which create limescale that binds to the heating element and walls. As the heater gets very hot very quickly it will “bake” the minerals to the inside of the unit. This limescale will reduce the efficiency of your water heater and can even break it. Therefore, you must perform proper maintenance on it. People that live in areas with really hard water (lots of calcium and magnesium) may need to maintain their unit once every year, while people in areas with softer water (or those that have a water softener) might not do this every 4 or 5 years.

Maintaining one of these units is a straight forward job. It will differ very slightly between manufacturers, but generally it is just a matter of rinsing it with undiluted white vinegar. This will remove any limescale or mineral build up on the heating elements.

You can take a look at the basic maintenance procedure with this guide.


Will I get instant hot water?

Actually, no you won’t. This is a common misconception about these types of heater. It will heat water instantly on-demand, but it will still need to travel through the plumbing lines. To get instant hot water you need to install a recirculation pump. These are available with many tankless models.

Do I need to upgrade the gas line?

Yes, possibly as they need a bigger gas line. Tankless heaters need more Btus because they use their energy over the period of a few seconds or minutes. A traditional system that uses a tank is able to use energy more steadily over a long period of time. The minimum gas line size is usually 3/4 inch and the size of the gas line upgrade will depend on the model and distance from the gas meter.

So it uses more gas than a traditional system?

No, they use the same Btus. The traditional system heats more steadily, but they both use the same amount of energy to do the same work. The tankless unit will save energy as it has a higher energy efficiency, and will only heat water when it is needed. A system with a tank will waste energy by continuously heating the water to maintain the desired temperature.

Why do some models need electricity and gas?

The gas supply is to heat the water. Most models are operated by digital controls. They use digital monitoring and have an electric ignition.

Will I need a water softener?

No, you don’t need one. However, if you live in an area that has really hard water, then a water softener would help to prolong the life of the water heater. Some kind of water treatment system to prevent scale build up in the water heater would be an advantage.

Will it save me money on my energy bills?

Yes. These systems are more energy efficient because they only heat water when it is needed. Traditional water heaters are lazy when it comes to energy efficiency because they are constantly in operation and use energy. all of the time If you choose a system with a really high energy efficiency ratings or an Energy Star certificate, you are likely to save even more each month.

Do they need regular maintenance?

They should be maintained around once a year. This is a simple job which involves rinsing the system with vinegar to remove limescale from the heating elements. If you have a water softener then this won’t have to be done as often. A whole house water filter would also help to prevent things like sediment from affecting the performance of the heater.

How much do they cost?

Tankless water heater prices vary from around $200- $1500. The prices change according to the size/output of the unit, energy efficiency rating, and general features a unit offers. The best tankless hot water heaters offer precise digital controls that let you strike an energy/heat balance that will save you the most money on your bills.

That brings us to the end of our hot water heater reviews and guide. If you have any questions then please don’t hesitate to ask away. We promise to reply promptly.

We’ll update this page as we find top rated water heaters that we feel add any value to the guide.

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