Best Tankless Water Heater of 2020 – The Comprehensive Guide

The majority of homeowners today choose to heat their hot water using tankless water heater systems. This is largely due to them being much more efficient than other forms of water heaters, such as storage heaters and furnaces. 

If you’re on the search for a new tankless water heater, then you ought to choose one that meets the needs of your hot water demands. It’s also important to choose one that’s efficient since this will help prevent energy wastage and curb unnecessary spending on your utility bill.

To achieve this goal, you need to consider the different types of tankless water heaters available and determine which size and fuel type are most suitable for your particular circumstances. For a more in-depth rundown check out our tankless water heater reviews below.

Tankless Water Heater Reviews Comparison Chart

Rheem RTG-84XLN
  • Heat output: 199,000 BTUs
  • 9.5 Gallons per Minute (GPM)
  • Direct-vent
  • On-demand heater

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Eccotemp FVI-12
  • Heat output: 80,000 BTUs
  • 4.8 Gallons per Minute (GPM)
  • Direct-vent
  • On-demand
  • heater

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Marey Power Gas 10L
  • Heat output: 42,000 BTUs
  • Up to 50 Gallons per Minute (GPM)
  • Power-vent
  • Storage heater
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Rinnai RUCS Series SE
  • Heat output: 71,000 BTUs
  • 3.1 Gallons per Minute (GPM)
  • On-demand
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EcoSmart ECO 27
  • Heat output: 92,000 BTUs
  • Up to Gallons per Minute (GPM)
  • On-demand
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Rinnai RLX94iN
  • Heat output: 192,000 BTUs
  • 9.8 Gallons per Minute (GPM)
  • On-demand
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Bosch Electric Mini-Tank
  • 3.2 Gallons per Minute (GPM)
  • Direct-vent
  • On-demand
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*All links above will take you to the latest prices on or you can read our best tankless water heater reviews below.

Founded in California all the way back in 1925, Rheem has a fantastic reputation, especially when it comes to their range of on-demand water heaters.

At 9.5 GPM, this condensing on-demand water heater is a good choice for the average sized family home.

A key advantage with on-demand tankless heaters is how easy they are to use, the digital display allows you to control the settings and monitor performance issues from the screen.

The display screen includes details regarding the water temperature and provides error code information if something is to falter. The unit comes with a set standard temperature but you can easily adjust this with the arrow keys, however, once you’ve set it up and established a temperature you feel comfortable with, there’s no real reason to do it again.

With any type of on-demand water heater, noise is unavoidable when in operation, but the Rheem is extremely quiet when running, which can be heard when you are using the hot water. But once it’s up and pumping out the warm water, it doesn’t make a significant amount of noise – which is a bonus.

As mentioned, this top rated tankless water heater unit has a hot water flow rate of 9.5 GPM making it a good choice for the average household. It also has an efficiency rating of 94%, combine this with the digital controls and it all helps you to conserve energy and save money

This gas powered condensing water heater by Takagi has a water flow of 10 gallons per minute, making it ideal for averaged sized home and medium-sized properties.

It’s also suitable for commercial properties such as small food outlets and beauty parlors.

To say it has a significant flow rate at an impressive 3650F, it will meet the hot water demands of medium-sized families, even in colder climates. 

This flow rate is good enough to provide adequate hot water for up to 4 bathrooms being used simultaneously in warmer climates, and around 3 in colder climates.  

However, for best results, ensure you use a low-flow showerhead if you intend on using multiple water outlets at once.

Regarding installation, it is a relatively simple stepwise process; you will require sufficient venting to the outdoors which can be achieved by using a horizontal or vertical PVC ventilation system.

However, bear in mind that unless experienced and equipped with all the necessary certification, installation should be carried out by a professional, so don’t forget to factor this into your budget.

Overall, the reputation and reviews of this unit make it clear that it is one of the best tankless gas water heaters available, so we definitely think its worth considering. 

This small and robust on-demand water heater is ideal for smaller properties, as well as cabins, garages and other out-buildings.

The black glass design is also extremely attractive, making it perfect for scenarios where it’s not easy to hide it away behind cabinet doors.

The modern appearance of the Eccotemp is also equipped with the specs including touch screen ability and an LCD screen that provides information on the chosen temperature and GPM rate.

It also has a built-in child lock function to prevent and kids causing mischief and for additional peace of mind.

This unit has a BTU rating of 80,000 so will be able to provide hot water at a temperature up to 350F when running at 4 GPM. The installation process should be more straightforward than larger units and is accompanies with a horizontal stainless steel ventilation kit – this is a great benefit and means you won’t have to spend more money on one at a later stage.

Another big advantage of this unit is how efficient it is – even though it’s only suitable for small properties, it only utilizes 2 Watts when not running and 1.07 when in operation. Certainly one of the best tankless water heater units out there for efficiency. 

Rinnai is a Japanese manufacturer that has been in the water heater business since the 1920s and has a solid reputation in the industry.

This condensing model with a maximum BTU of almost 200k is ideal for medium sized homes and will likely meet the water demands of up to 4 simultaneous applications.

The fact that it features second generation condensing technology means that it utilizes two heat exchangers. This means heat from the exhaust fumes are also used to heat the hot water, instead of being drawn out through the ventilation, making for increased efficiency and faster hot water. 

At 10 gallons per minute, this unit can deliver hot water to multiple applications at once. A good way to think about this is in terms of how many people are in your household and going to be using the hot water simultaneously, rather than the square foot of your property.

This provides a better indication of your requirements, for example, if you have 3 people and one is using a shower at 3 GPM, the other using the dishwasher at 2GPM and washing machine at 3 GPM, this water tank would probably meet your demand.

Benefits Of A Tankless Water Heater

Tankless water heaters are the latest innovation in water heating technology and as a result have solved many of the issues often associated with older models, such as storage water heaters.

One of the major advantages of tankless water heaters is on-demand hot water that won’t run out. This is in stark difference to storage water heaters that have a finite amount of water and often struggle to meet the water demands of large families and homes.

Another major advantage of tankless water heaters is the modest space required to house them, compared to storage heaters that often require a significant amount of floor space, tankless units can often be wall mounted and hidden away in cupboards meaning they free up square footage for other use.

Efficiency is a metric of heat transfer from the fuel source to the water itself. At present, tankless water heaters have an average efficiency rating above 80% Tankless water heaters are far more efficient than storage heaters since they don’t suffer from what is known as standby heat loss as water isn’t being heated constantly throughout the day. This helps conserve energy, meaning you will save a substantial amount on your fuel bill in comparison.

In real terms, the average consumer can save as much as 60% and at least 30% on heating water bills – based on the supposition that their usage does not increase. This is significant when you consider that the typical home in the US spends between $200 and $500 each year.

The average storage water heater can have a typical lifespan of as much as 12 years. On the other hand, tankless heaters can have a significantly longer life, reaching anywhere between 20 to 30 years. This is a result of the superior materials used in their construction.

Bear in mind that the downside of this is that you can expect to pay more in terms of up-front costs and installation. Yet over time, you will recoup these expenses when taking into account the energy savings you will make.

Types Of Tankless Water Heaters

Tankless gas heaters can be divided upon into the type of fuel they use, as well as the method by which they heat the water. The two most common forms of fuel are gas and electricity. As a result gas tankless water heaters and electric tankless water heaters remain the most popular.

Overall, gas water heaters remain most popular as gas is generally much more efficient and quicker at heating water. This is one their major advantages, which will ultimately help save you money. However, a potential downside of Gas-fired tankless water heaters is that they need ventilation, with the majority need vertical venting.

However, some units with low nitrous oxide emissions are equipped with power vents that can be vented horizontally. This is something to consider for homes where venting may present challenges.

As well as being divided in terms of fuel type, tankless water heaters can be divided into the mechanism by which they heat the water. These are as follows:

These are the earliest tankless heaters and utilize a heat exchanger to heat water on-demand. Due to their age, they are tried and tested design, which has been modified over the years to the extent that there are very few manufacturing problems reported. Disadvantages include them requiring costly ventilation systems such as stainless steel and have a reduced efficiency compared to the other types.

These are a newer type of tankless water heater that utilizes two heat exchangers as opposed to a single one. The second exchanger recycles exhaust heater to heat even more water, leading to higher efficiency. It also means their exhaust fumes are cooler and so cheaper ventilation can be used. Disadvantages include increased up-front price tag and similar to non-condensing types lower efficiency compared to hybrid units.

These are the latest type of tankless water heaters and utilize a water reservoir tank, which holds hot water, solving the common issue of low efficiency during periods of short use. This means that overall, hybrid models are the most efficient type of tankless water heaters, reaching well into the 90% range.

Other advantages include the fact that they can be used along with cheaper ventilation such as PVC and there isn’t as much of a delay between waiting for hot water to be sent to the faucet. However, bear in mind as these are the latest innovation, they are still being finessed in many regards and so there has been manufacturing issues reported.

What Size Water Heater Do You Need?

While gallon capacity, recovery rate, and first-hour rating are used when selecting traditional storage water heaters, tankless water heaters are chosen based on flow rate.

Therefore, when selecting a tankless hot water heater for your family disregard the capacity of the unit and instead think about the flow rate. Other important values given to tankless units, which are important when determining flow rate include BTU (British Thermal Unit) input and efficiency ratings.

It’s also important to note that although tankless units don’t run out of hot water like storage units, they may not heat water fast enough to meet all of your demands. This is why it’s important to think about your hot water use when you are making a decision based on size.

BTU value – This value is used to determine the temperature increase per 1 pound of water by 1 degree. Therefore, the higher the BTU value, the greater the flow rate. Typically, 190,000 BTUs are required to provide 5.7 GPM of water.

Flow rate – This is given in gallons per minute (GPM), which hinges on a given heat increase and typically falls into the 4 gallons to 10 gallons per minute categories. For example, a unit capable of supplying enough water for 3 water demands at once i.e. a single faucet and two showers is typically between 6 and 10 GPM.

Efficiency – The efficiency rating is important to consider if you want to make substantial energy savings, which in the long term will help save you money.

Efficiency is a metric of heat transfer from the fuel source to the hot water. The great thing is that today you can easily attain a tankless water heater with 90% and above efficiency rating.

Final Thoughts

Choosing an on-demand or tankless water heater is straightforward once you know what you’re hot water demands are going to be.

That’s why you need to go into buying mode knowing how many water outlets you’re likely to use at any one time.  Once you know this, you know you’re on track to making the right decision.

Other important factors include the brand – I would always advise buying from a manufacturer that’s been around for some time.

After all, a warranty is usually void if they go bust and the stories people buying a unit from a new brand that goes bust a few years down the line are more common than you may like to believe.

About the Author

Dave Miller is a HVAC technician with over 10 years in the industry. Dave created HeatTalk with the ambition for it to become a resource for individuals looking for answers, whether they be a layman, student or a professional.

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