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The Ultimate Guide to Tankless Water Heaters

Home owners are often in two minds when it comes to the type of water heaters they should install in their homes. On the one side, we have traditional tank water heaters. They’re bulky in size and they’re less ecologically friendly than tankless heaters.

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On the other side, tankless water heaters are becoming more popular as their price is dropping. They’re more convenient for installation and maintenance, plus, they consume less electric energy. In this ultimate guide to tankless water heaters, we’re going to discuss the main differences between tank and tankless heaters, as well as the key advantages of tankless heaters.

After that, we’ll provide the reviews of five top-notch tankless heaters.


Tank vs. tankless water heaters


In a tank water heater, water is kept in the tank, where it’s heated when the heater is switched on. However, when you turn the heater off, the water inside the heater gets cold after some time. As a result, you might waste electric energy to heat the same amount of water for several times.

Even if you keep the heater on all the time, as you consume the hot water from that tank, the water storage is being filled with cold water, which also has to be heated.

As such, tank water heaters are ecologically inefficient, especially when we apply the current efficiency standards for water heaters.

Tankless heaters, on the other hand, are made to avoid that standby energy loss, so typical for tank heaters.

In a tankless water heater, water is heated as it flows through the coil inside the unit.

This technology makes it possible for users to use hot water whenever they need it. They don’t have to wait for cold water to get hot in a tank, but it’s heated as it flows through the heater.

The downside of some tankless heaters is the limited amount of hot water that can be delivered per unit of time.

On average, these water heaters can provide 2-5 GPM (gallons per minute) of hot running water. This can be problematic for larger families or bigger households, since they might lack hot water when they’re simultaneously using several showers and household devices that need hot water.

That’s why some people decide to install two or more tankless heaters and have them joined together, to increase their output of hot water.

Some other people decide to install a heater per appliance that needs hot water and that way ensure steady water flow and temperature for all their needs.

Finally, you can go for a larger tankless water heater to cover all your needs, but it’s recommended to always consult a professional who will tell you whether or not one tankless heater can meet all your demands for hot water.


Electric and gas tankless water heaters


There are two major types of tankless water heaters: electric heaters and gas heaters.

Electric tankless heaters use the electric power to heat cold water. Since electricity is more affordable than gas in many parts of the world, electric tankless heaters are still more popular than their gas counterparts.

An electric tankless water heater is plugged into the grid and uses the electric power to heat the water running through it. Some modern heaters of this kind come with cutting-edge technologies that optimize both the electricity and water consumption. You can read about some of them later in the text.

Gas heaters, on the other hand, require a source of natural gas in order to work. You can get this problem solved in two different ways. On the one hand, you can connect your gas tankless heater to the local gas network.

On the other, you can get a portable tank of gas and use it as the gas source for your heater. This option will work for campers, tourists and people who often go to their holiday houses.

Also, gas heaters burn gas to heat water, which is why you need to vent the gas heater, in order to remove make the air in the heated place safe.

For all these reasons, most households opt for electric heaters.


The most prominent tankless water heaters


Rheem RTE 13 Electric Tankless Water Heater, 4 GPM


The first tankless water heater we’re going to present in this comprehensive guide is the Rheem RTE 13 Electric Tankless Water Heater.

The high-quality heat exchanger made of copper and brass comes with a 10-year warranty, which guarantees first-class heating performances and durability.

Since we’re living in the time of ecological awareness, it’s important to stress out that this heating device has the Energy Star label. This means that it’s categorized as a highly efficient water heater.

Two most common concerns regarding tankless water heaters are the energy efficiency and the speed of hot water delivery. As for the first consideration, the modulating heat exchanger makes this heater an ecologically friendly device. Also, no heat is lost in the standby mode and it emits no greenhouse gases.

You can easily set the temperature on the device itself, while the LEDs on the unit show whether the heater is active or in the standby mode.

When it comes to technical specs, here’s what this Rheem heater has to offer.

The wattage of the Rheem RTE 13 is 13kW and the voltage is 240 V. As for the water supply features, it delivers 4 gallons of water per minute (4 GPM).

What makes this heater a great point-of-use choice is its compact shape and size. Namely, its dimensions are 7.2 x 7.2 x 7.2 inches. When you know that it weighs 7.35 pounds, it becomes even more obvious why the Rheem RTE 13 can easily fit into many different spaces.

The Rheem RTE 13 is a great option for homes and bathrooms where it can be installed close to the shower unit and the bath. If you think in an economical way, you can reduce its heat to 60% or 70% of its full heat amplitude. That way, you’ll always have enough hot water for your needs and you’ll save some electricity along the way.

When compared to a tank water heater, you’ll pay a similar amount of money for the traditional heater and the Rheem RTE 13. Still, for an average water consumer, the latter will pay off in the first year and a half. After that, you can enjoy the ecological and convenient benefit of this tankless electric water heater.

As for the cons of this heater, some users have reported that it sometimes won’t turn on in case of lower water pressure. In addition to that, sometimes the hot water flow isn’t consistent, which might result in unexpected jerks of hot water from time to time.


EcoSmart ECO 11 Electric Tankless Water Heater


The next tankless water heater we’re going to analyze here is the EcoSmart ECO 11 electric heater.

Due to the self-modulating technology, originally patented by EcoSmart. In a nutshell, this tankless water heater and many other similar products made by EcoSmart control the energy and water consumption through the Flow Sensor technology. By modulating the current need for hot water, rather than switching the heater on and off, this technology represents a great blend of user friendliness and energy efficiency.

The EcoSmart ECO 11 comes with the WaterSense label, which means that it’s made to save water while providing you with enough hot water all the time. 

Another advantage of this heater is the option to adjust the temperature of the water degree by degree using the digital control on the heating unit.

As for the warranty, you get a lifetime warranty on the heat exchanger, the elements and the electronic parts. Still, it doesn’t recover the replacement procedure.

The EcoSmart ECO 11 perfectly works with one shower attached to it in colder environments, while in warmer climates you can connect two shower heads to a single EcoSmart unit.

Similar to the aforementioned Rheem RTE 13, the EcoSmart ECO 11 also comes with the 13kW wattage and 240 V voltage.

The dimensions of this device are 6.5 x 13.5 x 10 inches, with the weight of 6.5 pounds. As such, it’s a perfect choice for point-of-use settings, as well as for places with a low water flow.

The most specific disadvantage, or rather demand for this water heater is the electric service it requires. Namely, you’ll need 120 amps of electric service only for the EcoSmart ECO 11 if you want it to work properly. Because of that, contact a professional electrician before you buy this heater and check if it’s compatible with your wiring.


Stiebel Eltron Tempra Plus 24 kW with Self-Modulating Power Technology & Advanced Flow Control


Some homeowners can’t satisfy all their water-heating needs with smaller tankless heaters. If you’re one of them, Stiebel Eltron Tempra Plus 24 kW could be a great choice. The Tempra series is a well-known line of water heaters, which has been updated and improved in many sections.

For instance, the Stiebel Eltron Tempra Plus 24 kW model comes with the highly Advanced Flow Control technology. In simple terms, this feature eliminates the so called “cold water surprise”. If the demand for hot water is larger than the Tempra Plus can provide at the moment, Advanced Flow Control will reduce the water jet, but there won’t be any change in the temperature of the running water. Also, you can simply adjust the temperature of hot water with the user-friendly dial on the unit.

The electronic parts have also been improved, which makes them perfectly compatible with the present-day ecological standards.

Compared with modern tank water heaters, the Stiebel Eltron Tempra Plus 24 can reduce your electricity bill up to 20% and the manufacturer claims 99% energy efficiency with this tankless heater.

When comparing it with traditional tank heaters, this model leaves a lot of free space, which makes it perfect for wide range of real estates, from apartments and houses to holiday cottages.  

The major advantage of Stiebel Eltron Tempra Plus 24 over gas tankless water heaters is its affordability. Apart from that, its installation is much simpler than installing gas tankless heaters, mostly because you don’t have to bother with venting.

Finally, here are some key technical specs. The wattage of this tankless water heater is 24kW and the voltage is 240 V.  The electric service of the place in which you’ll be using the Tempra Plus 24 should support the minimum amperage of 2×50.

The dimensions of this water heater are 21.5 x 19.5 x 8.8 inches and the weight is 16.1 pounds.







Eccotemp L10 Portable Outdoor Tankless Water Heater


If you have a large backyard or a holiday house outside the town, you can make great use of an outdoor tankless water heater. One of the most prominent representatives of this group of portable heaters is the Eccotemp L10 gas tankless water heater.

The major concern with portable heaters is the functionality of batteries and the connectivity of the gas input. For this model, you need to use 2 D-cell batteries, which start the ignition of the heating system. As for the gas input, it has an integrated compression fitting. The only thing you need to do is connect a tank of liquid propane with the heater.

What you should also take care of when it comes to outdoor water heaters is the type of the water supply system. In case there’s no water supply network in the area where you install this heater, you can relax. The Eccotemp L10 is compatible with a 12-V water pump.

When it comes to water flow, this tankless water heater can provide you with the maximum of 2.6 GPM. These features will be sufficient for two devices using hot water to work simultaneously.

Since the Eccotemp L10 hasn’t been tested at the altitudes higher than 5500 feet, it’s recommended not to use it in higher areas.

The dimensions of this heater are 8 x 14 x 25.5 inches and the weight is 27 pounds. As such, it can fit into any average trunk and be taken wherever you go on holidays or excursions.

The most adequate surroundings for this gas tankless water heater are holiday cottages, ranches, camps and other outside areas. Additionally, you can even attach the Eccotemp L10 to your trailer, next to the rainwater tank, so as to make it even more ecologically efficient.

On the negative side, it might provide a little bit low output of hot water in areas with lower groundwater temperature. That’s why you should get the info about the groundwater temperature in your area and talk with the manufacturer before you decide to buy this practical water heater.







EcoSmart ECO 27 Electric Tankless Water Heater, 27 KW at 240 Volts


Another handy tankless water heater from the EcoSmart family, the EcoSmart ECO 27 device is a cutting-edge heating unit.

This model comes with the aforementioned Self-Modulating Technology, which enables the optimum consumption of water with the economical use of electric energy.

What puts this water heater ahead of the curve is the heating quality to provide 3 GPM at the minimum temperature of 37° F (2°C). As such, the EcoSmart ECO 27 is a perfect choice for people living in the colder parts of the world. It can provide enough hot water for two showers working at the same time in those weather conditions.

When used in warmer climates, the ECO 27 can heat enough water for several devices working simultaneously. In such conditions, this heater will provide you with hot water at the 6 GPM rate. All these features will meet the demands of most families that live in houses and this audience should go for this heater.

The sleek design of this EcoSmart device and the digital dial for temperature make this unit a visually appealing water heater, a well.

As for the electrical specifications of the ECO 27 water heater, its wattage is 27 kW – hence the number in its name – and the voltage is 240 V. Since it has the WaterSense technology, this heater will provide you with the required amount of hot water without wasting any additional water.

The dimensions are 3.6 x 17 x 17 inches, so it’s the largest heater of all the units reviewed in this article.

Obviously, the owners of smaller houses and apartments might find it too big for their needs.

Also, since the electrical requirements for installing this heater are three 40 amp double pole breakers, some home owners will find it too demanding.

Still, for large families that live in houses with potent electric service, the ECO 27 heater is a perfect choice.




In this day and age, energy efficiency is extremely important in terms of any electric device. When we draw the line below all the tankless water heaters presented in this text, one candidate gets ahead of the curve – the Stiebel Eltron Tempra Plus 24 kW. Its auto-modulation features save energy while generating enough hot water at every single moment, which Stiebel patented as Advanced Flow Control. We’ve already highlighted in the review of this heater that its energy efficiency rate reaches 99%.

Also, the heating chambers made of copper guarantee durability and high performance of the Tempra Plus 24 kW.

On the other side, it’s important to mention the Eccotemp L10 gas tankless heater, as the only unit from the gas specter of tankless water heaters in this review. Its size and dimensions make it a practical heater that can be easily installed on houses, cottages and trailers. Also, due to its simple installation, you can easily attach it to a plumbing system and connect a portable propane tank to it.

Now that you’ve read our reviews and seen our verdict, you can get the tankless water heater that will suit your needs. That way, you’ll start saving money and energy while enjoying the seamless flow of hot water in your household.





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