Best Tankless Water Heaters in 2021 – Buying Guide & Reviews

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Best Tankless Water Heaters in 2021

Planning to rebuild your house or give it an extensive retrofit? Consider taking advantage of the situation and give your water heating system an upgrade too, while you’re at it. Although installation can be expensive and complicated, having the best tankless water heater in the house will make your life a whole lot easier. Compared to traditional water heaters, it offers far greater convenience. Tankless heaters also help by being the more energy-efficient option, so can save you some money in the long run.

The first part of this article will be an in-depth buying guide to catch you up with everything you need to know about tankless water heaters. In the review section, we have a couple of great recommendations that might interest you.

Differences Between Traditional and Tankless Water Heaters

The most significant difference between traditional and tankless water heaters is that the latter does not use a storage tank. Instead, cold water is drawn directly into the heating unit, where it is rapidly heated. The water then goes directly to the point of use. This is the reason why tankless water heaters are also referred to as “on-demand heaters”. 

With traditional heaters, the hot water will go to a separate storage unit, and you will have to wait until the tank is full to use it (or risk running out of hot water halfway through your shower). 

In the conventional heater, if the hot water supply is not used up immediately, the heater will have to go to work repeatedly to keep it warm. This is the reason why, even though tankless water heaters are expensive to install initially, it’s worth the investment in the long-run as you save on your utility bill.

According to the U.S Department of Energy, tankless gas heaters can save over $108 when compared to traditional gas-firing heaters. Meanwhile, electric tankless heaters can save its users $44 annually when pitched against traditional electric heaters. 

Tankless water heaters are not perfect, since they have a much lower flow rate than tank-heaters. The average flow rate of tankless water heaters ranges from 2 to 5 gallons (7.6 to 15.2 liters) per minute. Meanwhile, because hot water has already been produced beforehand and stored away just waiting for you to use, there’s technically no effective flow rate for a traditional heater. If there’s still hot water in the tank, you can draw out and use as much as you want.

If you live in a large residence, the time it takes for the water to be heated, travel through the pipe, and to your shower can take up to several minutes (this is referred to as “lag time”). For this reason, while you will see a hefty saving on the heating bill, your water consumption rate will go way up. This is an essential notion to keep in mind, especially if you live in regions where water is more expensive than gas or electricity. 

How to Pick the Best Tankless Water Heaters


For the heater to transform cold pipe water into a warm shower, the unit makes use of a component called a heat exchanger. The exchanger’s job is to transfer heat from one source to another, specifically from what is called a “heating element” to the cold water.

The design of this heating element ultimately depends on the kind of fuel that your heater uses, which is either gas or electricity.

Tankless Gas Water Heater

In a gas tankless water heater, the heating element will be a gas-fired burner. A steady supply of either propane or natural gas keeps it firing. Since gas produces much fiercer heat than electric heating coils, gas heaters can provide hot water quicker and at a far higher volume than their electric counterpart (over 8 gallons per minute, or GPM). This is the biggest reason why large families tend to purchase gas heaters.

Tankless Gas Water Heater

The initial cost of a gas heater can be high- it is not hard to cross the $1,000 mark. An average gas heater can already cost north of $500 (the Rinnai V75iN, for example, is considered relatively affordable but still exceeds this pricing line.) The more fancy features and the better the performance a gas heater has, the more expensive it will be.

Aside from the unit cost, you will also have to worry about installation. Plumbers have to go through a lot of steps to make sure that the system is safe for use, especially since gas can be lethal when mishandled. This can add up costs rapidly.

One of the most expensive and complicated steps in the installation process is the heater’s vent. If you buy a non-condensing heater, despite the lower unit cost, you will have to pay for plumbers to install a sophisticated venting system. During combustion of the fuel, hot gases are produced by the heater. For non-condensing heaters, these gases are pushed through the vent and outside.

However, that is a highly inefficient method. The hot gases contain excess energy that could be used to further aid in the water heating process.

Exploiting that traditionally-wasted energy source is what condensing heaters do. They work by rerouting the hot steam and gas back to the heater and absorb the excess heat into the water stream to aid with heating further.

This arrangement also has an additional benefit: Condensing heaters require a considerably less elaborate venting arrangement. As the process draws a lot of heat out of the final gas that would be vented, instead of stainless steel which is the only material that can withstand the high heat of non-condensing heater’s emission, the vent of non-condensing heaters can be constructed out of cheap PVC.

As their design is much more sophisticated, the initial cost for a unit is far higher. Aside from eliminating the need for costly installation, because condensing heaters are highly efficient, they will be able to lift a substantial weight from your heating bill. In a non-condenser heater, this additional heat source is wasted entirely.

Gas burners can be much more affordable to run in comparison to electricity since gas is far cheaper in a lot of places, but before you commit, keep in mind that gas prices tend to fluctuate wildly. In the long-run,  experts believe that gas prices will skyrocket in a few years while everyone expects that electricity costs will remain relatively stable.

Gas heaters will require far more frequent and expensive maintenance too. You can do general maintenance yourself with the right knowledge and tools; however, we recommend hiring professionals whenever possible, especially when it comes to gas-line maintenance.

Tankless Electric Water Heater

A tankless electric water heater’s heating element works in a pretty similar fashion to a hot plate. High-voltage electricity will heat a series of heating coils inside the heat exchanger, which will quickly boil up the water. Electric water heaters have few parts and are not as complicated as gas heaters. They are cheap, small (so small they can be stored in a cupboard), and are easy to install. They do not require a vent, though you may need to rewire the electrical system inside the house to accommodate the new heater.

Tankless Electric Water Heater

Electric heaters produce hot water at a much lower rate than gas heaters. A typical electric unit can produce about 8 GPM of hot water in ideal conditions. But in non-ideal conditions like in cold climates, the flow rate is going to suffer. At sub-zero, you should expect the performance of your electric heater to be halved. Gas heaters are also affected by temperature, but since they are much more powerful, the effect is less punishing on their performance. 

The cost of electricity is usually a little bit higher than gas, but it is much more stable. Electricity production is gradually becoming greener, requires less maintenance, and is generally a much safer option than gas. If your house is in an area where there tend to be natural disasters such as tornadoes, earthquakes, etc., an electric heater is a far safer bet than a gas heater.

Energy Factor (EF)

The energy factor denotes the energy efficiency of a heater. EF is calculated based on the volume of hot water produced for every unit of fuel that is consumed. The higher the EF rating is, the more energy-efficient the system will be. 

A trick to use when looking at water heaters is to find the Energy Star label. For a tankless water heater to be qualified for an Energy Star, it must have an EF of 0.67 or above. Condensing water heaters are a separate category, to be eligible for an Energy Star, they must have an EF of a whopping 0.8.

However, energy efficiency is not always equal to a lighter bill, and cost-effectiveness depends mostly on the type of fuel your heater uses. An electric water heater, for example, may have an EF that’s significantly higher than a gas heater. But since electricity is usually more expensive than gas, you will find that the operating cost of a gas heater is considerably lower.


We can’t stress just how crucial proper sizing is for a new water heater. A heater too limited will be extremely annoying when it doesn’t produce enough hot water for your family. If you end up with a water heater that’s too big, you’ll be paying for more than you need.

This depends on two factors. The first being your family’s water consumption and habits. Second is the number of appliances that will be using that water in the house (showers, dishwashers, etc.). Sum all of these appliances flow rates, and you will have a rough idea of what the flow rate of your heater should be to support the entire household.

For example, let’s say that your house has four people, and there are two showers, a kitchen sink, and a dishwasher. If in the evening, all four members of the family use all of the appliances at the same time, peak water consumption would be very large, amounting to about 8 GPM.  So it makes sense that you would aim for a heater that can provide that much water.

Safety Mechanisms

Tankless water heaters also outperform here and are much safer than traditional water heaters. A big reason is that water simply travels through the pipe, gets heated up, and is delivered immediately to you; there’s no fear of pressure build-up.

Tankless water heaters are also less prone to leaking than their older counterparts, so the risk of your house being damaged will be reduced as a result.

Tankless electric water heaters even have a protection system to prevent overheating or overloading, automatically shutting down the unit before it could cause damage to the system or the house.

And that’s it for the buying guide section! These are everything that you ought to keep in mind while you’re selecting the best tankless water heater for your home. In the review section below, we have selected a range of great tankless water heaters that we think you will find interesting.

Reviews of Best Tankless Water Heaters in 2021

As promised, here is our selection of the best tankless water heaters in 2021:

  1. EcoSmart ECO 27 – Best to Buy Tankless Water Heater
  2. EcoSmart ECO 11 Best Budget Tankless Water Heater
  3. Rinnai V65iN – Best Tankless Gas Water Heater
  4. Rinnai V-Series V75iP – Best Propane Tankless Water Heater
  5. Stiebel Eltron Tempra 36 Plus – Best Wholehouse Electric Tankless Water Heater
  6. Camplux AY132S – Best RV Tankless Water Heater

1. EcoSmart ECO 27 – Best to Buy Tankless Water Heater

The EcoSmart ECO 27 has a great balance of aesthetic, compactness, and performance. The fact that it is packed with a good range of features, all within an ideal price tag, has served to make it one of the most appealing deals to consumers looking for a well-rounded electric tankless water heater.

EcoSmart ECO 27 Electric Tankless Water Heater


  • Affordable
  • Adequate performance
  • High energy efficiency
  • Digital control interface
  • Durable design
  • Various safety mechanisms
  • Simple installation process
  • Comprehensive warranty


  • Not fit for large homes
  • Underperforms in cold weather

Performance-wise, it is the most potent affordable-range water heater that EcoSmart is offering (the most powerful is the ECO 36, but the price is higher.) When pushed to its limit, the ECO 27 is capable of outputting an ample flow rate of 6.5 GPM. In places with warm temperatures (68°F and up), this flow rate can support about four showerheads plus a sink. 

However, in colder regions with the temperature nearer to 32°F, expect its performance to be halved to about 3 GPM. So this might not be your top pick if you live in Alaska or are wintering up north.

This heater wouldn’t  be out of place in a smart home with its digital control interface and ability to self-regulate. The modulating computer helps it achieve a remarkable 99.8% energy efficiency, although for reasons unknown to us, the unit does not have an Energy Star label. 

The control panel at the front of the unit allows you to set the desired water temperature in 1-degree increments with an easy-to-use knob. The current temperature is displayed on the front panel digital screen.

The ECO 27’s performance will largely depend on the temperature of the water flowing into the unit. The warmer the water, the more efficient and quicker the unit will be at delivering piping-hot water to you. 

Your electrical system needs to be able to supply 240 volts to the unit. The heater has three heating elements which draw a total of 27 kilowatts. It will also have a maximum amperage draw of roughly 113 amps. The unit features an automatic overheating/overloading prevention mechanism to keep it from damaging the electrical system of the house or even itself in case of freak accidents.

One of the many pluses of the ECO 27 is that it’s low-maintenance. A stable power supply, a water pipe, and a comfy storage space is just about everything you need to start having on-demand hot water.  With all of the vital components cast out of metal like copper and stainless steel, your maintenance workload is reduced significantly. Additionally, these materials allow for better conductivity, rust-resistance, and higher strength and longevity. 

Finally, in case any of the components break down, since the unit is covered by the company’s limited lifetime warranty policy, it is always possible to find replacement parts.

2. EcoSmart ECO 11 – Best Budget Tankless Water Heater

If you’re looking for a more budget-friendly solution to your hot water problem, the EcoSmart ECO 11 is a decent choice. Though it is priced at a suspiciously affordable point, this water heater does the job really well. You won’t be missing out on a lot of extra features when compared to more expensive variants either.

EcoSmart ECO 11 Electric Tankless Water Heater


  • Affordable
  • Energy-efficient
  • Digital control interface
  • Easy to store
  • Comprehensive warranty


  • Extremely limited flow rate
  • Underperforms in cold weather

Its energy efficiency is almost absolute with 99.8% of the power used wholly devoted to the heating process. Even with the impressive energy efficiency rating, we are still puzzled as to why it has yet to be Energy Star qualified.

The easy-to-use digital control of the ECO 27 is still there on the ECO 11. The current temperature setting is displayed on a digital screen. The adjustment knob underneath, used  to set up the temperature, completes the intuitive, user-friendly control scheme that EcoSmart’s heaters are known for.

The ECO 11 requires a 240-volt electrical grid to operate with the maximum amperage draw clocking in at about 33 amps. The heating elements use about 8 kilowatts worth of power at peak power usage. 

Due to the ECO 11’s standard 2 GPM output, it is only suitable for small to medium-sized residences. In ideal conditions (with weather from 67 degrees and up), it should be able to supply hot water to two sinks along with one shower. In more frigid climates, the best you can get would be about two sinks running at the same time. Colder than this and its performance would only allow it to be a small Point of Use heater rather than a house-wide hot water supplier.

As a result, if you have a large house or family to cater to or you live in colder regions, this heater is unfortunately out of the question.

Thanks to its compact size and the fact it’s lightweight, it is not difficult at all to find a storage space for the heater inside the house. It can virtually be stored just about anywhere as long as that spot has access to the water and electric line.

This unit is also covered by a lifetime warranty policy. All of the parts can be found and replaced if they break down during operation. 

3. Rinnai V65iN – Best Tankless Gas Water Heater

While electric heaters may be more sustainable, convenient, and cheaper to install, their weak flow rate can make them off-putting to a lot of people. If you’re part of this crowd, then a tankless gas heater seems to be the only choice. 

Rinnai V65IN Tankless Water Heater


  • Affordable
  • Great performance
  • Smart app available
  • Various safety mechanisms
  • Durable design
  • Comprehensive warranty


  • Long lag time
  • Complicated, expensive installation

The Rinnai V65iN is a natural gas-burning heater that has excellent performance, safety, and reliability, along with an affordable price tag.

Depending on the temperature of the groundwater flowing into the unit, it can output a maximum of 6.5 GPM of hot water. With such a flow rate, it will be able to support three showers and maybe a kitchen sink running in tandem. For the heater to achieve this, it burns from 10,300 to 150,000 BTU (British Thermal Unit). A flow rate of 6.5 GPM is more than enough to cover the needs of a large residence, powering three to four showers at the same time with little difficulty. 

The only thing that we have to complain about is that, just like any other gas heaters, it suffers from long lag time. Customers have reported that they usually have to wait for up to 40 seconds at a time for the temperature to rise as they desired.

Safety is handled by a series of valves, which automatically switch on and off to protect the unit and the house. There’s a temperature lock to make sure that there won’t be any sudden changes in the water’s temperature. An anti-frost feature is also available for users in colder regions.

The majority of the heater’s components are made out of rigid metals and even though a few parts are thermoplastic, most consumers reported the heater lasting for a long time. You’ll also receive the benefits from the 10-year warranty period on the heat exchanger, 1-year on labor, and 5-year on parts.

There is also the option to get the Control-R Wi-Fi module. The module essentially allows you to issue voice commands to the heater and control it from the company’s app on your smartphone, effectively turning the heater “smart”.

Since this is a non-condensing heater, you’ll have to discuss with a plumber about venting. Other than that, the rest of the installation process will be relatively painless thanks to the one-piece design of the heater.

4. Rinnai V-Series V75iP – Best Propane Tankless Water Heater 

Many houses don’t have a natural gas pipeline, and if your home is in this group, a good alternative is to get a propane tankless water heater. Although propane is slightly more expensive per BTU, the cost is balanced out by it having higher energy per gallon when compared to natural gas. Additionally, propane is widely available, and also comes in easily-transportable tanks.

Rinnai V Series HE Tankless Hot Water Heater


  • Natural gas alternative
  • Heavy-duty performance
  • Smart app available
  • Various safety mechanisms
  • Durable design
  • Comprehensive warranty


  • Requires a vent
  • Propane is more expensive

The Rinnai V75iP has a high flow rate, an ideal energy factor for a propane-running tankless water heater, and a robust indoor design. Better yet, for all that it offers, this heater remains a relatively budget selection.

The V75iP has a 7.5 GPM flow rate while performing at its best (that’s four showers running at the same time and there’s still enough capacity left to run a kitchen faucet.) It should have little trouble catering to the hot water needs of large residences.

Other features are pretty much similar to the previously mentioned Rinnai V65iN. It is a non-condensing heater, so it will require you to set up a vent. The power line requirement is the same, and the unit is also compatible with the optional Control-R Wi-Fi module.

Additionally, you will get the numerous safety valves, temperature lock, and anti-frost features, just like with the V65iN. The warranty policy backing this heater has 10 years on the heat exchanger, 1 year on labor, and 5 years on parts.

5. Stiebel Eltron Tempra 36 Plus – Best Whole House Electric Tankless Water Heater

The Stiebel Eltron Tempra 36 Plus has the best of both worlds: it doesn’t require complicated installation and maintenance (since it is an electric tankless unit), but it also has a hot water yield rivaling heavy-duty gas heaters. This has made it a popular choice for people that have high hot water demand yet want to keep both the budget and construction works on the down-low.

Stiebel Eltron Tankless Heater


  • Powerful
  • Highly energy-efficient
  • Digital control interface
  • Various safety sensors
  • Compact
  • Great warranty policy


  • Unit price is high
  • Can hike power bill

The Tempra 36 Plus is the most powerful electric tankless water heater that Stiebel Eltron has got in its portfolio. In the ideal temperature (above 72°F), this heater can generate a steady 7.5 GPM flow rate, enough to sustain four showers and two sinks running at the same time. Even at sub-optimal water temperature (Under 42°F), this unit is still able to operate two showers and a bathroom sink.

It is highly energy-efficient, having an EF of 0.99. Thanks to the self-modulating computer inside, it will also help to keep your electric bill low.

This heater will draw about 36 kilowatts in its operation and will require that you have a stable current of 240 volts. The maximum amperage draw is about 150 amps, and the minimum recommended household electrical service is 300 amps.

The controls are digital. There is a digitized screen that displays the current water temperature setting and all information that you need to know about its operation. Underneath the screen is a temperature-adjusting knob for you to change the temperature. The unit also has memory buttons for you and your family to set the warmth that each of you likes best for easier switching.

Along with all this, the unit is also loaded with a system of sensors called Advanced Flow Control to keep the water temperature constant and to aid in saving water. The compact size means the entire heater can fit inside a small closet, which makes finding a space to store it reasonably simple.

A complete warranty package composed of 7 years on leakage and 3 years on parts comes with the unit.

6. Camplux AY132S – Best RV Tankless Water Heater

Portability is the most prized value for RV-ers. But what makes this propane tankless water heater so popular is that it also offers excellent performance for such a compact and mobile setup.

Camplux 5L 1.32 GPM Portable Tankless Water Heater


  • Portable
  • Highly adaptable
  • Adequate performance
  • Packed with safety features


  • Limited warranty policy
  • Ineffective at high altitude

In terms of performance, since the unit is meant to be as compact and light as possible, its 1.32 GPM output is relatively adequate. It can operate even without being connected to a full power supply and can be jump-started by two D batteries. The propane canister installed should have an internal pressure of about 0.4 PSI. The small propane burner inside is rated at 28,000 BTU per hour.

An important thing that makes the AY132S so effective as an RV water heater is that it has a very low start-up water pressure at only 3.0 PSI. Considering the spotty water supply campgrounds often have, this is a huge plus. In case the water pressure inside the RV is too low to use comfortably, users always have the option to operate the heater from out of a 12-volt water pump.

The design of the unit is robust and packed with a wide range of safety features. Because the unit will pump propane fumes directly into the environment, there is an Oxygen Depletion Sensor Protection shut-off feature for when you’re using it indoors. The burner will automatically shut off when it detects the oxygen level in the air dropping low enough that it could potentially damage your health. 

There’s also an overheating protection sensor, flame failure device to prevent flammable gas from reaching the burner when you shut it down, and an anti-freezing feature.

Mind that although the heater can heat water to near-boiling, it should not be used as a source for drinking water. It is also not recommended that you bring it along to a height above 2,000 feet.

Unlike other products on the list, Camplux only offers a 1-year warranty for the AY132S.

Tips to Take Better Care of Your Tankless Water Heater

Flush the Unit 

Hard water refers to water with a high concentration of minerals like calcium and magnesium, as opposed to soft water. If you have hard water running through the pipe feeding your heating unit, it is highly recommended that you descale (or flush) the unit at least once a year. On the other hand, if you live in an area with soft water or you already have a water softener installed, your heater should be able to go for several years before it needs a flush-out.

Typically, the manufacturer will tell you the steps to flushing the heater in the user’s manual. Only use the descaling agent that the manufacturer recommends. If you’d like a home remedy, white vinegar is the most popular choice.

Test the Pressure Relief Valve 

Pressure relief valves are critical safety components. Their job is to protect the unit from literally exploding when the water pressure inside rises to a dangerously high level. This is the reason why you must give it a test every once in a while by opening and closing it to make sure that it’s working correctly. 

To test, turn the lever until water drips out of the unit and onto the ground. Be careful because the water coming out will be hot. Once that is done, close the valve and make sure that the water also shuts off along with it.

Clean the Air Filter

If your heater has an air filter, it is required that you clean it every once in a while to make sure that it is not clogged up by dirt, dust, debris, pollen, lint, etc. Simply clean everything with a soft, damp cloth.


Concluding the article, we genuinely hope that the information has helped you in understanding the best tankless water heaters better and that you have found the article useful in building an informed purchase decision.

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