Best Tankless Water Heaters – (Reviews & Guide 2021)

Having a reliable water heater is something that nearly everyone takes for granted. We are so used to having hot water at our disposal all the time, but our water heater finally breaks down, we finally realize how important they are.

Having a dependable water heater that is energy efficient is something that gives homeowners peace of mind. With the introduction of the tankless water heater, we have even more efficiency, and thanks to the quick heating element of the tankless system, we are saving gallons of water with each shower.

Choosing the best tankless water heater can be a daunting task for many. There are many different brands, variations, heating agents, and much more to decipher that it can be difficult to know exactly which tankless water heater is best for you.

By following our in-depth reviews of tankless water heaters on the market and our buying guide, you will learn everything you need (and more) to make an informed decision. Tankless water heaters are loaded with features and that your entire home can benefit from it. If you have decided that tankless is right for you, then you are in the right place!

Best Tankless Water Heater Reviews

1.Rheem RTGH-95DVLN 9.5 GPM Natural Gas Tankless Water Heater

Rheem-RTGH-95DVLNHighlighted Features

  • It comes with a digital display that shows temperature setting and visible alerts if the machine needs to be serviced.
  • There is a built-in fan that dispels the natural gas through ventilation.
  • It can operate in altitudes as high as 9,840 feet above sea level.
  • This tankless water heater produces 9.8 gallons of water each minute.

Rheem is one of the most trusted names in water heater technology. They are constantly evolving their entire product line, whether that is their tankless systems or any other product.
The RTGH-95DVLN is Rheem’s top of the line unit, and it is easy to see why with the long list of features.

First off, the standard 12-year warranty is huge when it comes to water heaters. The standard across the industry is 9 years, and the Rheem blows that out of the water.

The user-friendly technical details that are included with the Rheem system make management and maintenance a breeze. The all-digital temperature and error code display is crisp and easy to read. The wireless remote allows for full control of your unit from anywhere in your home. One thing we loved is the higher water capacity of the Rheem 95DVLN. It can produce 9.5-gallons of hot water per minute, which is enough to run multiple showers at once.

What We Like:

  • The unit is wrapped in overheat film that helps keep the unit cooler and safer.
  • There is a digital remote included that allows you to control all aspects of your tankless water heater.
  • These things include setting the temperature and turning the system onto vacation mode.
  • It can be installed with either a 3-inch PVC pipe or 2-inch PVC pipe, although 3-inch is preferred for venting reasons.
  • The built-in fan blower does a great job getting rid of excess gasses and does not add any size to the unit.
  • We love the size of the unit. It does not take up a lot of space on the wall and can fit in most utility closets.

What We Didn’t Like:

  • Only one of the two valves required is included by Rheem.


2. Rinnai V65iN High-Efficiency Tankless Hot Water Heater

Rinnai-V65iNHighlighted Features

  • Rinnai offers multiple different variations of this natural gas water heater so you can choose which one suits your needs.
  • They also offer propane systems to ensure they will be effective with your heat source.
    The factory warranty varies by component:
    – 120 Months for the heat exchanger.
    – 12 months on labor.
    – 60 months on all other components.
  • Depending on the version you choose, the flow rate is between 6.5 and 9.4 GPM.
  • Hot water recirculates throughout your pipes when the unit is not in use, allowing for zero wait time between receiving hot water.

The Rinnai system is an ultra-customizable system that is available in a variety of variations to ensure that you are getting the best product for your home.
It comes in natural gas and propane fuel options and is loaded with user-friendly features that allow for easy adjustments and safety features. It will come preset with a 120-Degree (F) maximum temp but is adjustable to allow for temperatures as high as 140 (F.)

The mobile app was a game-breaker for Rinnai and allows you to have full control of your system from anywhere in the world.

This Energy Star rated system does not waste energy or water. Because of the tankless nature of the system, it can recirculate hot water throughout your water pipes to ensure that the second you turn on the water, hot water will be available.

With standard tank water heaters, each time you initiate a hot water valve, there is a long wait period between the water turning hot. On average, this wastes over 100 ounces of water. This problem is completely alleviated by the Rinnai tankless water heater!

The Rinnai system is an ultra-customizable system that is available in a variety of variations to ensure that you are getting the best product for your home.

It comes in natural gas and propane fuel options and is loaded with user-friendly features that allow for easy adjustments and safety features. It will come preset with a 120-Degree (F) maximum temp but is adjustable to allow for temperatures as high as 140 (F.)

The mobile app was a game-breaker for Rinnai and allows you to have full control of your system from anywhere in the world.

This Energy Star rated system does not waste energy or water. Because of the tankless nature of the system, it can recirculate hot water throughout your water pipes to ensure that the second you turn on the water, hot water will be available.

With standard tank water heaters, each time you initiate a hot water valve, there is a long wait period between the water turning hot. On average, this wastes over 100 ounces of water. This problem is completely alleviated by the Rinnai tankless water heater!

What We Like:

  • There is a mobile app included that allows you to control your tankless water heater from anywhere in the world.
  • The size of the Rinnai tankless water heater is perfect if you are short on wall space.
  • It is designed to be installed by the homeowner, and they provide great and detailed manuals that help with this.
  • The water inlet and outlets are ¾-inch which is the most common pipe size in homes.
  • There is an included, Temperature Lock function that will not allow the water temperature to be changed without the access.

What We Didn’t Like:

  • There is a special condensing kit required for installs, and it is not included.


3.Takagi T-H3-DV-N Condensing High-Efficiency Tankless Water Heater

Takagi-T-H3-DV-NHighlighted Features

  • It has a maximum capacity of 10 GPM.
  • This tankless water heater runs on natural gas only.
  • It has an Energy Star rating that guarantees it is energy efficient.
  • The tankless water heater is very small; it takes up virtually no space on the wall and only weighs 59 pounds.

We love simple products that do not have too many moving parts or endless steps to get to the point. With the Takagi tankless water heater, you will have the simplest controls with easy to read LED screens to let you know exactly what your tankless water heater is up to.

The first thing you will notice is that the unit is ultra-compact. This is especially nice for homes or apartments that want to upgrade their water heater but are worried about space constraints.
This Energy Star rated tankless water heater weighs less than 60 pounds, which is one of the lightest units that we have seen.

This makes installation easier and gives homeowners peace of mind that it will not have any issues with staying built into the wall.

The temperature control unit on the Takagi tankless water heater is among the simplest we have seen. Up and down arrows are quick reacting and allow you to set the temperature to the exact degree you prefer. Between these features and the 10-GPM flow rate, the Takagi is a great option for many homes.

What We Like:

  • We tested this model in a high-altitude environment around 8,500 feet and have seen no issues.
  • The size is nearly perfect. It is about the size of a carry-on suitcase which makes installation easy.
  • There is no waiting time between opening a hot water valve and the water becoming hot.
  • The 10-gallon per minute water flow rate is among the best that we have tested to this point.
  • This tankless water heater is loaded with safety features that ensure overheating will not occur or any excess gas being dispelled.

What We Didn’t Like:

  • Neither of the valves is included with the initial purchase.


4.Camplux 16L Outdoor 4.22 GPM Tankless Water Heater

Camplux-16LHighlighted Features

  • This tankless water heater is designed for outdoor use with propane as the heating agent, and the water is delivered from the unit to the hose directly.
  • There is a rubber water hose included with the system that delivers hot water.
  • The unit has anti-freeze technology that allows it to work in cold weather.
  • It has a maximum flow rate of 4.22 gallons per minute.

If you live out in the woods or a mountainous area, this tankless water heater is a great choice for a multitude of reasons.

When it comes to the need for hot water in an off-the-grid environment, the Camplux is loaded with features that make it a great choice.

To start, it weighs less than 40 pounds and is one of the smallest tankless water heaters that we have reviewed at this point. Due to its size, it is easy to bring with you to the campsite or cabin.
Another reason it works well off the grid is the ignition type. It uses propane to generate heat, which is also mobile, but it also uses D-Cell batteries to ignite. There is no need for any electrical plug or generator for this system to operate and provide hot water right away.

The included rubber water hose and shower sprayer are a great addition to the package as well. After installing this to a flat vertical surface, the rubber water hose does a great job acting as a showerhead, and you can bathe virtually anywhere!

What We Like:

  • The digital temperature display is crystal clear and allows us to set the temperature to the exact degree.
  • This system is designed for campsites or cabins, which makes it light and mobile.
  • It is ignited by 2 D-Cell batteries, which means you do not need a power source to make this system heat.
  • The water was heated up essentially right when the water valve was opened, it was amazing.
  • It comes with all the valves and connectors needed to use it right out of the box.

What We Didn’t Like:

  • There is a built-in 20-minute safety timer that cannot be changed or adjusted.

5.Eccotemp I12-NG Tankless Water Heater

Eccotemp-I12-NGHighlighted Features

  • You can choose between a liquid propane model or a natural gas model.
  • There is a crisp LED display that is easy to read and adjust.
  • It has been tested in elevations as high as 5500 feet and it is not suggested to be used higher than that.
  • There is no pilot light, and the system activates immediately when hot water is demanded.

The Eccotemp tankless water heater is one of the more sleek and modern looking tankless water heaters we have ever seen.It is all black and is covered with tempered glass that causes the LED display to be clearer than much other tankless water heater’s displays.

The controls on this tankless water heater are easy to use and respond right away to even the slightest adjustments. We love how energy efficient the system is as well. Because there is no pilot light, the system is efficient and safer.

The water fittings are the right size for many homes and are simple to connect to your home’s main water supply. The response time to the water being heated up is almost instant. This will save water in the long term and because this is a tankless water heater, it will provide endless hot water. The electronic ignition switch is a simple design but works right away and is one of our favorite features.

What We  Like:

  • It uses a standard 110-volt electrical outlet, making it easy to install most places.
  • The water fittings are ½-inch, which is the standard across most homes, and this made it easy to install.
  • We love the modern and sleek look of this unit. It is jet black and looks sharp on the wall.
  • The ignition switch is electronic, which is widely regarded as safer and works instantly.
  • Because there is no pilot light, it reduces the amount of energy it consumes, making it more efficient.

What We Didn’t Like:

  • The maximum elevation is much lower than comparable models.


6.Westinghouse 11 GPM Tankless Water Heater

Westinghouse-11Highlighted Features

  • This unit is Energy Star certified, ensuring you are getting the most efficient heater.
  • It boasts 199,000 BTUs to ensure hot water flows endlessly.
  • The heat exchanger is made from stainless steel and is strong and tough.
  • It is designed to use liquid propane as its main fuel source.

If you are looking for the highest capacity tankless water heater you can find, the Westinghouse may be your best choice.
It has a massive 11 GPM rating, which is enough to handle a 6-bedroom house with simultaneous use. They did not skimp on the safety features either.

There are built-in indicators for water leaks and gas leaks that let you sleep tight, knowing that if anything is happening with your tankless water heater, you will be warned.

The venting pipe attachments are easy to work with, the included clamps are great for quick, but tight connections that allow for proper venting without the need for epoxy or any other type of pipe glue. It has a maximum BTU-rating of 199,000, which is more than enough to keep up with the demand for water throughout the home.

There is no waiting for hot water with this unit either, as you open the hot water valve in the shower or sink, it comes right away!

What We Like:

  • The 11 GPM rating is the highest we have tested so far and will work for any home.
  • There is a built-in leak detector that lets the homeowner know if there is an internal leak within the unit.
  • The mounting bracket and hardware are strong and sturdy. Often, we get poorly made brackets, but we were impressed with the Westinghouse unit.
  • It has a 10-1 turndown ratio that allows the system to match energy usage on demand.
  • The vent pipes come with clamps that allow for easy installation.

What We Didn’t Like:

  • Technical support is lacking, and the unit is one of the heaviest we have seen.


7.Rinnai V94iN High-Efficiency Tankless Hot Water Heater

Rinnai-V94iN-High-EfficiencyHighlighted Features

  • This is the highest capacity flow rate tankless heater that Rinnai offers at 9.4 GPM.
  • It comes in either a natural gas version or liquid propane heating element type.
  • There is an included factory warranty of 120 months on the unit and 60 months on all the components.
  • This system uses 40% less energy than traditional tank water heaters.

Making another appearance in our top 10 list is the Rinnai natural gas tankless water heater. This version is different than our previous review due to the capacity of this unit being 9.4 GPM.
The Rinnai is known for its versatility, and the number of places that this unit will fit into your home is endless. Think of a carry-on size suitcase, it is about that big and is light enough to be easily installed to the wall with no fear of it coming down.

It comes out of the box with WiFi enabled so that you can immediately hook it up and have complete control over the system. One of my favorite parts of the system is the ability to control the entire unit from your phone.

You could be anywhere in the world and realize that you forgot to place the system into vacation mode. You can do this from your phone app if you are connected to WiFi or an LTE network. This will save time and money!

What We Like:

  • The wait time for hot water is zero; it immediately produces hot water from any valve
  • There is a cool mobile app that allows you to control every aspect of your Rinnai tankless water heater.
  • It is light and compact, which makes installation simple and straightforward.
  • There is no drop in water pressure, and the water remains hot for hours of testing.
  • The unit is one of the quietest tankless water heaters we have tested up to this point; you can barely hear it.

What We Didn’t Like:

  • The isolation valves that are required do not come with the package and must be installed separately.


8.Noritz NR66ODNG Outdoor Tankless Water Heater

Noritz-NR66ODNGHighlighted Features

  • This system is designed to be used with natural gas.
  • The Noritz system is an outdoor tankless water heater that can push put 6.5 GPM.
  • It weighs only 36 pounds, which makes it the lightest system that we have reviewed this far.
  • There is an included 12-year warranty on the heat exchanger and a 5-year warranty on the components.

The Noritz is the smallest unit that we have tested to this point, but even with its small size, it can keep up with the bigger ones with ease. While this system would not be the best choice for a large home, if you have a standard 3-bedroom home, it is hard to beat the value you get from the Noritz system. Right off the bat, we have an Energy Star appliance that delivers instant hot water that is virtually endless! What more could you want?

One of our favorite things about this system is that all the connections are metal or brass. This is far more durable than a plastic connector and gives us peace of mind that there will not be a failure any time soon.

Because it is designed for outdoor use, the venting occurs naturally, and therefore, you do not need to worry about reworking your pipes or venting at all!

What We Like:

  • This is the most mobile system that we have reviewed; it is easy to bring with you virtually anywhere.
  • It comes with an Energy Star rating, which is always preferred.
  • For the price, this is one of the best values you can get from a tankless water heater.
  • The rigid design allows for it to be installed virtually anywhere, whether that is the backyard or at the campsite.
  • There is no end in sight to the amount of hot water it can produce, we tested it for hours, and it kept up just fine.

What We Didn’t Like:

  • The required valve kit for installation is not included with the system.


9.MAREY 3.1 GPM Liquid Propane Gas Digital Panel Tankless Water Heater

MAREY-3.1-GPMHighlighted Feature

  • This system runs on 2 D-Cell batteries for use off the grid.
  • You can choose between natural gas or liquid propane option, both boasting the same features.
  • There is a digital screen that shows you the water temp.
  • It comes with ½-inch venting output for smaller or more compact home pipes.

If you are an adventurer or prefer to spend your time at the campsite or off the grid, the MAREY liquid propane tankless water heater may be the right heater for you.
It is smaller than a carry-on suitcase and weighs less than most, too. It can be brought with you to the most remote campsites, and because it runs on liquid propane, you can bring the fuel source with you too!

The heater is operated by 2 D-Cell batteries that will give you hours of water heater operation without the need for a long chord or any other power source.

The versatility the system allows for makes it a fan favorite as well. While it is designed to be used in an off-grid situation, the price tag is ultra-appealing to all homeowners.

Many off-grid systems do not include the vent pipe connectors, but the MAREY checks this box and adds an important safety function that allows this system to be used in all homes.

What We Like:

  • The size of this tankless water makes it’s the most mobile and easiest to pack water heater we have found.
  • The D-Cell batteries that it uses to run last a long time and will handle many trips.
  • There is no water wasted with this system; it only pushes hot water and recirculates if not in use.
  • The 3.1 GPM may seem small, but it is more than enough for off the grid homes.
  • There are easy to use temperature controls on the unit, and the screen is crystal clear.

What We Didn’t Like:

  • It takes a little longer to produce hot water compared to other tankless systems.


10. EZ Tankless Deluxe On-Demand Tankless Water Heater

EZ-Tankless-DeluxeHighlighted Features

  • This tankless water heater runs on liquid propane and can handle two bathrooms at once.
  • It has an energy factor of 0.88, which makes it an Energy Star certified heater.
  • The maximum capacity of this unit is 4.4 GPM, which enough for many homes.
  • It comes with a 5-year warranty on the heat exchanger and a 1-year warranty on all other components.

The EZ Tankless water heater is a DIY homeowner’s dream. Right away, you will notice that the unit comes with additional venting pipe material to make your life easier when it comes to the install.

All the connectors and inlet valves are made from heavy-duty materials and are simple and easy to use. The small and compact size of the system makes it easy for any homeowner to maneuver and place in the perfect spot.

While the flow rate is not as high as some more high-end models, it is a great number for the price you are paying for this unit. You are truly getting a great value.

The mounting bracket and hardware included are strong, and I have no fear that they will fail anytime soon. I was most impressed by EZ Tankless’s customer support. We always test their online and phone support, and the amount of detail and technical help you can get is the best on our list.

What We Like:

  • This was one of the easiest tankless heaters we have installed to date; everything is user friendly.
  • It comes with a standard vent pipe and elbow to make things easier with the installation.
  • We are very impressed with the technical support that EZ Tankless provides.
  • The added safety features like overheat protection and pressure relief valve are nice to have for a model at this price point.
  • There is a maximum temperature of 149 degrees Fahrenheit which is hot enough for nearly anything.

What We Didn’t Like:

  • The heating capacity slows down the flow rate as the water gets hotter and hotter.


How Does a Tankless Water Heater Work?

Tankless water heaters revolutionized the way that we heat the water throughout our home.

Instead of holding water in a large tank and heating collected water like a standard water heater, the water is heated as it flows through the tankless water heater. By using an internal heating element that immediately heats water and produces an endless amount of hot water.

There will be an internal pilot light, or an electronic ignition will take the cold water that came into the tankless water heater, and it will spit out hot water.

One of the things that make them so popular is the immediate healing that occurs. This is due to most tankless systems having the ability to recirculate unused hot water.

Which is Better, Gas, or Electric Tankless Water Heater?

When choosing between a gas or electric tankless water heater, it will largely depend on your specific situation. But there are pros and cons for each type of device, and using this information will help you determine the right tankless water heater for you.

Gas Tankless Water Heater

Water Usage and Need

o Tankless gas water heaters can produce more hot water per minute than an electric tankless water heater. Because gas is widely regarded as the fastest way to heat the water as it is brought into the tankless system, it can keep up with the demand for hot water that large homes may require.

Available Energy Source

o Most homes are set up for gas intake in a utility closest or sometimes in the corner of a basement; this makes it easy to install a tankless gas water heater in your home.
o With electric water heaters, you MUST have a 240-Volt plugin near the main water supply. This is usually not available in many homes and can be expensive to have outlets converted.

Long Term Operating Costs

o Electric tankless water heaters are known as a high-powered appliance.

o Therefore, they require a lot of energy to operate, especially in larger homes with multiple bathrooms. Over time, the costs of operating a gas tankless water heater will be less than an electric model. With most tankless water heaters offering a 9+ year warranty, this can be substantial.

Electric Tankless Water Heater

Up-Front Cost

o With electric water heaters, there are fewer parts included for ventilation and gas line connection; therefore, the upfront cost will almost always be lower than a gas tankless water heater. The only requirement for an electric water heater is a sufficient electrical supply that can work with the electric water heater that you chose.


o There is a requirement that gas water heaters require that electric systems do not need it. This is the proper ventilation and vent pipe requirements that gas water heaters need to safely dispel the natural gas or propane that was used during the heating process. This process of connecting venting and gas dissipation can lead to longer installation times and is typically more expensive to install as well.


o One of the most popular reasons that electric tankless water heaters are popular is the lack of maintenance. There is a small filter that the water goes through on many units that requires the occasional cleaning, but other than that, electronic water heaters are virtually maintenance-free. Gas water heaters require annual maintenance to ensure vent connections and gas connections are solid. It also requires more frequent filter cleaning.

Tankless Water Heaters VS Traditional Tank Water Heaters

There is a long-term debate regarding whether the tankless water heater is the best choice for all homes. There are some geographical things to consider, and while both options are tried and proven heating methods, there are situations where both are good decisions.

Tankless Water Heaters


o With the evolution of the tankless water heater, manufacturers have been able to make tankless systems more efficient than their counterparts. They will require less energy than tank systems because a tank that is holding cold water needs to use all its energy to heat the available water while tankless systems heat water as it is brought into the unit.

Water Capacity and Time

o Because there is no storage tank with the tankless system, there is no limit to the amount of water that you can have access to. With a traditional water tank, there is a maximum amount of water available, and you may run the chance of running out the water entirely.

Additionally, there is usually a wait time of 20-30 seconds for the water to heat up with traditional water heaters. With tankless systems, because the water is heated as it flows through the system, you will have access to the hot water right away.

Traditional Tank Water Heaters

Significantly Lower Cost

o One of the reasons many people continue to use a standard tank water heating system is because of the cheaper costs of purchasing the unit. Tankless water heaters can be significantly higher in cost than the traditional system. Depending on whether you are going with electric or gas, the price can sometimes be doubled for a tankless water heater.


o It is widely regarded that the installation required to replace a standard tank water heater is much cheaper than the tankless models. Tankless systems require a lot of changes to be installed, especially when you are replacing a standard tank system with a tankless system. Most plumbers will charge less to install a standard tank water heater than a tankless system as well.

How Efficient are Gas Tankless Water Heaters?

Tankless gas water heaters are the epitome of efficiency when it comes to tankless water heaters. They especially excel in homes that use less than 50 gallons of water per day.

They can be 30-40% more efficient than standard gas water heaters that use a tank reservoir. Because natural gas tankless water heaters heat water the quickest out of any type of water heater, you will notice that your system uses less energy to heat the water supply and therefore, will save on long term energy bills.

What Size Tankless Water Heater Do I Need?

The perfect size of the tankless water heater will vary from person to person. It will depend on the amount of water that your home uses each day, and many times, the number of bathrooms in your home will dictate this as well.

Tankless water heaters measure their capacity by how many gallons of hot water they can produce per minute. The higher the number, the more water it can handle, and therefore, the more hot water you can have available each minute.

Larger homes will require a higher capacity tankless water heater than smaller homes.

Most tankless water heaters will come with multiple different capacity ratings that you can choose from. The higher the capacity, the more costly the unit will be.

I suggest to people that if they have four bathrooms, they will need something higher than 9 GPM. This will ensure hot water can be distributed throughout. If your home has less, you may want to figure out how much water your family uses per day and ensure that the capacity can keep up with all bathrooms in the home.

What is the Advantage of a Tankless Water Heater?

There are numerous advantages to a tankless water heating system when compared to the traditional tank-style water heater.

In addition to the aspects we covered earlier, the most loved aspect of a tankless water heater is the zero-waiting time for hot water.

With tank systems, there is usually a 25-30 second wait for hot water to come out of your showerhead or faucet.
Tankless water heaters produce hot water immediately. This is amazing for two reasons.

The first reason is that you are not sitting there for 30 seconds, constantly checking water temperature from the faucet or shower. This is a waste of time!

The other reason is the amount of water wasted. With a tank water heater, the amount of water you will waste with each shower is equal to 100s of gallons per month. The water efficiency of the tankless water heater is significantly better than the standard water heater.

What Is The Downside Of A Tankless Water Heater?

Keep in mind that there are a few drawbacks of the tankless style water heater. In addition to the up-front costs being significantly higher along with higher installation cost, you will notice that they are not as proficient as standard tank heaters in colder climates or higher altitudes.

Because the tankless system heats water as it is flowing through the system if the water being brought in is extremely cold, it will take longer for the water to heat up, and it will slow down the production of water.

Keep this in mind if you live in colder states. If this is the case, there are numerous tankless options available today that can produce enough hot water for most homes, and many systems feature anti-freezing technology to ensure water is heated quickly.

How to Choose a Tankless Water Heater

Power Input

Before choosing the best tankless water heater for you, you must decide if you are going with electric or gas.

We covered this extensively at the beginning of the buying guide, but remember, electric heaters will need a 240-Volt power plug nearby the gas line. Without one of these, your electric tankless water heater will not be able to be installed.

Flow Rate

When it comes to choosing the best tankless hot water heater for your home, the flow rate should be at the top of the list of things to investigate. With tankless water heaters, flow rate refers to the amount of water the system can produce each minute.

These rates will vary between systems, but many high-quality systems will come with numerous different options to choose from when it comes to flow rate.

You should expect that the higher the flow rate, the more it will cost but if you have a large home or use a ton of water, then it is worth it.

There are many options that are sufficient for many families that range from 3-10 GPM. But to get the best possible performance, you will want to ensure your research to find the best tankless water heater for you.

The number that you want to be aware of is 50 gallons. If your home uses more than 50 gallons of hot water per day, then you will want to ensure that you buy a tankless water heater that can handle a higher capacity.

Remember, there are numerous appliances that use hot water and you MUST take these into account as well. The last thing you want is to spend the money on a tankless water heater and it cannot keep up with your needs.


British Thermal Units, or more commonly known as, BTUs are a measurement that is used by many home appliances that require heating or cooling.

The actual BTU measurement calculates the amount of heat/energy required to raise the temperature of the water by one degree Fahrenheit.

BTU ratings will vary from system to system but it is important to understand that the higher the BTU rating, the higher-powered the heating element is and it can raise the temperature of the water faster and raise the temperature of more water.

When it comes to residential tankless water heaters, the BTU rating can range from 100,000-200,000.

This is an important thing to consider because if you are dealing with a cold-water source, lower BTU outputs may struggle to keep up with the heating demands.

Additionally, if you are mulling over choosing a higher flow rated tankless water heater, lower BTU outputs may not be able to keep up either. Many units that do have a higher flow rate now ensure that the BTU output is sufficient for almost any scenario.


Venting is one of the most important aspects when installing and using a gas water heater.

Without proper venting, a disaster can happen if there is a spark or the gas that was supposed to be vented is not done so properly.

You will notice that there are typically 2 sizes of vent pipe attachments with many tankless water heaters. This is to provide you with some installation flexibility.

Many older homes will use ½-inch vent piping and while this is still considered sufficient, many homes and tankless water systems perform best with ¾-inch venting in place.

Remember, venting only applies to gas water heaters but if you are thinking of going from a standard tank water heater to a gas tankless system, you will need to be sure that venting pipes that you have are the correct size for the new tankless system you are going to get.

As I mentioned, many systems are capable of handling either ½-inch or ¾-inch, but not all of them. You MUST ensure that your gas venting pipes are capable of being connected to your new tankless system. If required, many plumbers can change out venting pipe for a more efficient ¾-inch size if you prefer.

Energy Factor

The term, Energy Factor is often thrown around regarding water heaters, but few people know what it means.

The energy factor is calculated by dividing the amount of energy the water heater uses by the entire machine’s required energy needed to power it.

This may not mean much to you right now but in September of 2010, Energy Star started labeling any water heating device that is considered efficient and these labels are now considered the gold star in energy efficiency.

A water heater must have an energy factor calculation (see above) that is over 0.67 to qualify for the Energy Star label. Tankless electric water heaters will usually have a better chance of hitting these numbers and almost always have better energy factors than their gas counterparts.

However, electric tankless water heaters are usually 2-3 times more expensive to run than a gas tankless water heater. You will need to identify which is more valuable to you when choosing the best tankless hot water heater for your home.

Professional or DIY Installation?

Many home appliances and home improvement devices are now being designed with simplicity in mind, especially regarding the installation process.

Homeowners do not want to spend hundreds of extra dollars on installation costs on top of the money they are already spending.

Because of this, many tankless water heaters come with instructions and detailed manuals to help you through this process. But we have a few rules we follow when it comes to installation and nearly all of them revolve around whether your tankless water heater is electric or gas.

Tankless Gas Water Heaters


You will have to connect the venting pipes to the tankless unit correctly to avoid any gas leaks. Without this, there can be major issues with fire safety and the air you are breathing within your home.

Attaching the vent pipes can be simple but if you are upgrading from a standard tank water heater to a tankless system, odds are you will have to move around the venting pipes within your home, which is a tough ask for a lot of people.

Gas Connection

We never suggest to homeowners that they install gas appliances unless they have a plumbing or other relevant experience. You must ensure that the main gas source is completely shut off and when you attach the gas line to the gas valve on your tankless water heater, it must be done correctly and as strong as possible. The possible effects are just too high to mess with it.


Unless you have dealt with gas before, we strongly suggest hiring a professional. Especially if there is going to be the need to move venting pipe or gas line around to make the system work.

Tankless Electric Water Heater

Sufficient Power

With electric, there is no need for venting or gas connectors, you simply need to plug the system into a 220-Volt power outlet, connect the water and you are good to go! Remember, before you buy an electric water heater, you must ensure that you have enough power in your utility closet or room that will allow for the system to run.

If you do not have a 220-Volt plug, DO NOT try to do this yourself, you will need to hire an electrician. However, most of the time, if you do go electric, there will already be a 220-Volt outlet nearby.

Water Connections

If your water pipes are copper and they need to be maneuvered to fit your new tankless water heater, you may want to look for help.

If it were me, I would try and replace the water connectors with flexible stainless-steel hosing that allows them to be moved in any direction. Water connections are easy overall, but if you are dealing with a full water line replacement off the main, then you may be more comfortable with hiring a plumber to help you out!


o If you have the power outlet that is sufficient to run the unit, then you are good to go to do this yourself. Water connections are simple and with the manuals and instructions that high-quality tankless water systems come with, you should be good to make a strong connection!

Frequently Asked Questions and Answered

Do high altitudes affect my gas tankless water heater?

Yes! This is an important measurement to consider when choosing the tankless water heater for you.

The further up we go above sea level, the higher the atmospheric pressure, and therefore, the gas will become more volatile. Every quality tankless water heater will have an altitude rating.
They will range from 5,000-10,000 feet above sea level, sometimes higher. If this is a concern for you, make sure you check the rating on the tankless water heater.

Can you replace a tank water heater with a tankless?

Of course, you can! This is what most people who have a tankless water heater have had to do.

When it comes to replacing the old tank system, the install can be a little trickier when it comes to moving vent pipes, water connectors, and getting rid of that old heavy tank! But once you go tankless, the install from there on out is a breeze.

Will one gas tankless water heater be enough to heat my entire home?

This will depend entirely on the size of the home, but usually, you will be able to find a tankless system that can keep up with your demands.
Look for one with a higher maximum flow rate if this is a concern. If you have 5+ bathrooms, you may need to investigate higher-priced specialty units that can handle these homes.

What is the average life of a tankless water heater?

This will vary from system to system, but tankless water heaters were designed to last for decades.

The reason that tank water heaters were replaced so often was that they would leak from their water reservoir. With a tankless system, there is no chance of stagnant leaks and water is not sitting in the unit all the time corroding away at the system.

Warranties will last 12+ years but many people do not need to replace their tankless water heaters for 20 years.


Tankless water heaters are the technology of the future for most homes. The amount of space they save, the lack of water tank leaks and so many more factors make them a great choice for any home.

We understand that there are dozens of options on the market and choosing the best tankless water heater may seem difficult. But we are confident that you have all the information you need to make an informed and educated decision.

By following our in-depth review guide and using our buying guide to your advantage, you will easily be able to answer those tough questions regarding which model, or which flow rate is right for my home. We are sure that no matter which direction you go, you will choose the best on-demand tankless water heater for you and your home.

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Bob Allen
About Bob Allen

Bob has been a plumber for 15 years and loves it! He has always been interested in Plumbing from an early age and has the cuts and bruises to prove it as he set out to work with fix leaks, replace faucets, and make home improvements.