9 Best Indoor Tankless Water Heaters on the 2021 Market

indoor tankless water heater

Most of the tankless water heaters are indoor installation, they are more convenient in using and has a long service life. Because of the hot demand, there are many brands and many types of indoor tankless water heaters on the market of 2020. In order to better help you choose the most suitable one, we made detailed reviews of the best indoor tankless water heater for you.

Table of Contents show

The Top 9 Probably Best Indoor Tankless Water Heaters on the Market!

How to Choose the Best Indoor Tankless Water Heater

Various aspects go into the selection of the ultimate tankless water heater. Usually, you will need to be careful in the selection process. This determines the value for money you get in the long run. Take the time to observe the following variables in this pursuit.

• Decide on the source of fuel

Most often, you will need to choose between electric and gas-fired tankless water heaters. While both will provide you with an unrivaled performance for indoor use, they tend to strive in different areas.

There is no denying that electric tankless water heaters are more popular, thanks to how accessible they tend to be. While they guarantee you the ultimate performance, they are less suitable for the entire household. We could attribute this to the high cost of electrical upgrades. Besides, they are less safe.

In contrast, you will fall in love with how powerful gas-powered tankless water heaters are. It is for this reason that they have become the best bet for whole-house uses. All you will need to do is select the right size, and you will be good to go.

• Confirm the cost

Indoor tankless water heaters come with a relatively high upfront cost. However, that is not to say that you will not get an affordable unit. Take the time to identify a device that you will afford comfortably. This way, you will no longer need to worry about financial constraints at the end of the day.

While at it, you should be sure of the maintenance costs attached to your unit. For cost-effectiveness, lower maintenance expenses will come in handy for you. Gas-fired products tend to be much more affordable and even long-lasting. With this option, you will be sure of the ultimate satisfaction.

• Check the size

The size you choose will often depend on your needs and preferences. Usually, your focus will be on the GPM rate provided by the device, with a higher one being much better. Usually, higher GPM rates will come in handy as your family increases. On the other hand, a GPM rating of about 3.5 will be enough for a single occupant or small family. Such will be the right time to add all the GPM ratings of the devices in your house, as this will ensure you make suitable choices.

• Confirm the temperature rise

It would help if you were sure of the temperature rise required right from the onset. Usually, the temperature rise in warm climates tends to be much higher than in colder ones. In most cases, a heater that provides you with 50 to 55 degrees temperature rise will suit your needs.

• Confirm the maximum number of devices in your house

Unless you understand how many units you need in your home, getting the convenience you envision will remain a mirage. The number of devices you need will be based on how much water you use on average. For instance, if you live alone, a single unit will be enough for you. In contrast, you will have to increase the same if you have a bigger family.

The 9 Best Indoor Tankless Water Heaters Reviews

There are many brands and types of indoor tankless water heaters on the market of 2020, in order to help you choose the most suitable one, we have made detailed reviews for you as follow:

1. Best Indoor Tankless Water Heater – Rinnai RUC98iN Ultra Series Tankless Water Heater

tankless water heating systems for homes
residential tankless water heater





  • 9.8 GPM flow rate

The flow rate of this unit reaches as high as 9.8 gallons, it is able to support three or four bathrooms use the same time. The high flow rate of it also enables to supply constant hot water for you. It takes up 20 seconds for the water to heat up in the units.

  • 2 venting options

It offers two venting options, one is concentric PVC and the other is twin-pipe, so you can choose whichever is easy to be installed. The temperature of it can reach as high as 185 degrees F, making it possible for commercial use with the commercial remote.

  • Energy efficient

The power requirements range from 15200 to 199000 BTU per hour, the higher power requirements are, as more powerful as it is. The energy-efficient rating is as high as 0.95. But it needs only 2 watts to keep the machine up and running.


  1. 2 venting options
  2. High energy efficient
  3. Quiet working performance
  4. Unlimited hot water
  5. 5 years warranty on the part
  6. Multiple faucets and showers use simultaneously


Need to be installed by professional

2. Best Natural Gas – Rinnai V65IN 6.6 GPM Indoor Low NOx Tankless Water Heater

best indoor tankless water heater
tankless water heater for a house





  • Low NOx design

This unit meets California and Texas NOx Emissions Standards, maximum BTU is 150000, and the maximum energy factor is 0.82. Being a natural gas indoor tankless water heater, it is quite an energy efficient.

  • 6.6 GPM

The flow rate of this unit is 6.6 gallons per minute, it can handle two showers use the same time in warm areas. It supports constantly hot water for you.

  • Special venting

One thing you need to be aware of is that it requires special venting and needs to place near an outside wall for venting, it requires the aluminum interior vent pipe with PVC outer pipe.


  • Lightweight and compact design
  • Quiet working condition
  • One button turns on and off for vacation
  • Constantly hot water supply
  • 10-year warranty for heating exchanger
  • Easy installation


Needs special venting

3. Best Electric – Stiebel Eltron Tempra Plus 24 kW Tankless Water Heater

residential tankless water heater
home tankless water heater





  • 5 gallons per minute of water flow

The unit provides about 5 gallons of water per minute, which is a high flow rate machine. It is able to raise the water by 54 degrees F at 3 GPM. It has built-in advanced flow control modules to regulate water pressure by itself.

  • Stable temperature

It has an advanced flow control system in order to control water temperature in different flow levels, it is suitable for people in demand for occasional hot water. It has high-level electronic parts and a reliable cover to promise long service life of it.

  • Energy efficient

Stiebel boasts that the energy rating reaches as high as 99% and full power modulations enable large power of the machine. Also, it adopts self-modulating technology to save more energy.


  1. Quiet working condition
  2. Compact design, perfect for small studio use
  3. Ideal in places where supplied water is under 45 degrees F
  4. Full power modulation
  5. High technology adopt


Difficult to install, need 240v power and heavy-duty wiring

4. Best Cheap – Eccotemp FVI-12 Natural Gas Tankless Water Heater

best indoor tankless water heaters
best tankless water heater home use





  • 3.6 GPM

The flow rate of this unit is 3.5 gallons per minute, it is able to provide one shower and one low rated kitchen faucet at the same time. It is said to have a high capacity, but actually, it is ideal in a studio family use.

  • Digital temperature control

Temperature shows on the screen of the unit, and two buttons are set to adjust the water temperature, one is for flow rate while the other is gas settings. But it is quite difficult to adjust to the exact temperature you want.

  • Stylish compact shape

It is designed to light and compact, occupying only small piece of land of your home. It adopts a safe electronic ignition system, you can plug it into a standard 120v electrical outlet with a UL-listed cord.


  1. Energy saver
  2. Deliver hot water in a few seconds
  3. Efficient power ventilation
  4. Perfect for small house use
  5. Manual water temperature control
  6. Digital temperature control


Hard to get the temperature you want exactly

5. Best Energy Efficient – Takagi T-KJr2-IN-LP Indoor Tankless Water Heater

best tankless water heater for apartment
best residential tankless water heater





  • 150 degrees F temperature

The maximum temperature of this unit reaches as high as 150 degrees, perfectly meets the demand for residential use. It demands minimal maintenance during the whole using process.

  • 6.6 GPM flow rate

The flow rate of the unit is up to 6.6 gallons per minute, it provides constant hot water no matter for the climate or season. But in the cooler region, the flow rate may drop to 3-5 GPM.

  • Light compact size

It is the lightest and smallest one among all the Takagi products, you can easily install it anywhere you want. The power input of it is 140000 BTU per hour, and energy-efficient reaches 81%. But as a propane tankless water heater, it has more upfront costs in venting the gas to outdoor.


  1. Digital remote enabled
  2. Multiple bathroom use available
  3. Demands minimal maintenance
  4. Light-weighted
  5. Easy to be installed


The working noise can be heard

6. Best Condensing – Takagi T-H3-DV-N High-Efficiency Natural Gas Indoor Tankless Water Heater

residential tankless water heater reviews
indoor tankless water heater reviews





  • 185 degrees F temperature

The maximum temperature of it reaches as high as 185 degrees F, able to meet the demand of both residential and commercial use. But the waiting time of the hot water may be a bit long, takes around 1 minute.

  • 10 GPM large flow rate

This unit provides 10 gallons per minute of water flow, the huge flow rate provides you with constant hot water. It demands 199000 BTU per hour to perform in the best way, which is a highly powerful natural gas tankless water heater.

  • Set up simply

It is easy to set up, just adding several gas lines. Venting facilities are needed for venting gas to outdoor. It weights light and has a compact shape, can be installed anywhere you want.


  1. Remote control available with a controller
  2. High-temperature range
  3. Powerful enough
  4. Commercial & residential use
  5. Lightweight and compact shape
  6. Huge water flow


Needs to be installed by professionals

7. Naiven NPE-240-A Tankless Gas Water Heater

indoor tankless water heater
top rated indoor tankless water heater





  • ComfortFlow technology equipped

This unit is regarded as a high technological tankless water heater, it has a built-in hot buffer tank and recirculation pump, in order to eliminate cold water sandwiches and save water bills by reducing the waiting time for hot water.

  • Stable water temperature

The temperature of it keeps stable all the using time, the internal technology enables it quickly correct the temperature once it draws stop suddenly. The external interface shows water temperature and error codes. You can turn the machine off easily with the button.

  • Condensing technology

The condensing technology of it recovers the unused extra heat to reduce energy consumption and carbon dioxide emissions. It keeps the exhausted temperature low, it provides up to 0.97 UEF, which is a highly energy-efficient type.


  1. Hot buffer tank and recirculation pump built-in
  2. Clear installation and using instructions
  3. Short waiting time for hot water.
  4. Intelligent preheating technology
  5. Easy operated
  6. Powerful
  7. Large flow rate enabled


Slight working noise can be heard

8. Best Compact Electric – Atmor 27kW/240V Electric Indoor Use Tankless Water Heater

best tankless water heaters for home
best home tankless water heater





  • Digital temperature control

The digital temperature control enables you to set water temperature in increments of 1 degree, temperature, and error codes show on the screen. An easy operation setting makes it easy to adjust the temperature accurately.

  • Advanced ThermoPro technology

It is equipped with advanced Atmor’s ThermoPro self-modulating system, it regulates the amount of energy required to heat water. And it is able to automatically detect water flow, turn it on and off by itself, so as to eliminate wasted water flow and lower the water consumption.

  • 90-135 degrees F

Temperature range of the unit reaches between 90-135 degrees F, it proves to save about 50% electricity bill each month. Durable stainless steel interior and corrosion resistance performance allow for high heat efficiency and longer life expectancy.


  1. set temperature in increments of 1 degree.
  2. Durable stainless steel interior
  3. Save 50% on electricity bill
  4. Self-modulating system regulates the amount of energy required to heat water
  5. Automatically detect water flow
  6. Small footprint


Need to install a pressure relief device, and you need to buy it from manufacturer

9. Best Propane – Eccotemp i12-LP Indoor Tankless Water Heater

best tankless water heater for home
best indoor tankless water heater





  • 3 GPM flow rate

The flow rate of this unit is 3 gallons per minute, it activates only when hot water is demanded, no pilot light is needs and much energy consumption is reduced. It is said to use as a whole home tank, supporting two things at the same time, but we still suggest it be used for a tiny or small home.

  • Modern design

Sleek modern design and easy operated LED display control enables to adjust water temperature easily. Black tempered glass front panel is set to show temperature, automatic temperature controls with energy-saving mode, and child lock technology are set for avoiding unintentionally adjusting.

  • Safe ignition

It requires a safe electronic ignition system, you need to plug it into standard 110 v electrical outlet with UL-listed cord.


  1. Energy efficient
  2. Horizontal stainless steel vent kit
  3. Safe electronic ignition system
  4. Automatic temperature control
  5. Sleek modern design
  6. Easy operation


It needs to be plugged in

Indoor Tankless Water Heater Price

Price levels of each type of indoor tankless water heaters are different, it depends on the applications, flow rate, and power of the machine. Normally the whole house types are more expensive than the point of use types. And the price of gas, propane and electric tankless water heaters are also different to a large extent.

Apart from heating machine prices, you should also regard using costs as an important factor. To some of the water heaters, the using costs are even expensive than the purchasing price. It is influenced by the energy-efficient and waiting time of the machine. Besides, the installation and maintenance costs are also a large sum of money.

Only after integrating the two elements of costs together can you choose the most suitable and cost-effective one. If you want to know more details about the best indoor tankless water heaters on the market, you can check it out on Amazon freely.

tankless gas indoor water heater
tankless water heater gas indoor

Features of Indoor Tankless Water Heater

1. Long service life

The using life of an indoor tankless water heater is quite long, installed inside the home. the heating machine is not affected by bad weather, such as wind, rain, or long term erosion by complicated outdoor weather. Thus the service life of indoor tankless water heater reaches as long as 10-15 years, some even reach 20 years.

2. Various specifications

For indoor tankless water heater, the specifications and types are various, giving you more options and choices. Large flow rate indoor tankless water heaters such as whole-house tankless water heaters can be used for a large family, and portable type can be used for a small tiny home. Different specifications will meet the different demands of yours.

3. Flexible installation spots

The installation spots of indoor tankless water heater can be quite flexible, you can either install it on point of use or in the bathroom for shower use. If you do not have much space in the bathroom, you can also install it somewhere convenient in the kitchen.

4. Large flow rate

Not all the indoor tankless water heater has a large flow rate, for some point of use tankless water heaters, the flow rate can be so low as 2 GPM. But as most of them are used for supporting multiple bathrooms at the same time, the flow rate of indoor tankless water heaters is normally large.

best residential tankless water heater
best tankless water heater residential

What Types of Indoor Tankless Water Heaters Should I Choose?

According to the using applications, indoor tankless water heaters can be divided into whole-house type and point of use type.

Whole-house tankless water heater needs to support multiple bathrooms or faucets use, thus the flow rate and power are both large, reaching 9 GPM even. It can also be used as the commercial tankless water heater. We have made detailed whole house tankless water heaters reviews for you, you can check out for more information.

Point of use tankless water heater is quite small and compact in shape, some of which are small enough to be installed right under the kitchen sink. The flow rate is normally small, reaching around 3 GPM. Of course, some large flow rate types can also be used for point of use tankless water heaters, you just need to install near the application fixture and the waiting time can be shortened to a large extent. For more information on point of use types, please have a look at our best point of use tankless water heater reviews.

Based on the energy power source, they can be divided into the natural gas tankless water heater, propane tankless water heater as well as the electric tankless water heater.

Which Is Best, Propane, Gas, Or Electric Tankless Water Heater?

As for indoor tankless water heaters, both natural gas and propane types need to install ventilation facilities along with the heating machine to let out wasted gas, but not for an electric one.

Indoor propane tankless water heater is quite a clean machine, it does little harm to the environment. The power and flow rate of it is a bit higher than the electric one.

Tankless gas indoor water heater, however, can sometimes adopt propane as major power too. The power is normally large and can be used as whole house tankless water heater. Using the costs of gas types is much cheaper.

The electric tankless water heater is quite a flexibility on its installation spots, it can be installed anywhere you want because no ventilation facilities are required. But the using costs of it are relatively high.

There are no absolutely best indoor tankless water heaters, because the size of families, budgets, home locations, applications, and also daily water use is different for each family. Each of the three types of tankless water heaters has its own advantages and shortcomings, before selecting, you need to take all the factors into consideration. If you have trouble in choosing, or want to know more information on each type, please check out more on Amazon or on our reviews we made for you.

residential tankless water heater reviews
indoor tankless water heater reviews

The Best Tankless Water Heaters

Indoor Tankless Water Heater vs. Outdoor Tankless Water Heaters

The indoor tankless water heater is installed at home, either on the wall of the bathroom or kitchen, so it is hardly affected by the weather. However, outdoor tankless water heaters need to stay outside after installation, it needs an enclosure to prevent the machine from being corroded by rain or sunshine for a long time. Even with the protection cover, it is affected to a large extent. Therefore, compared with indoor tankless water heaters, the service life of the outdoor type can be a bit shorter.

Indoor tankless water heater installation can be more flexible than outdoor types, for outdoor tankless water heater, it needs to be installed right outside the bathroom wall for the short waiting time of hot water. But as for indoor types, you can install wherever is convenient.

The other difference between the indoor tankless water heater and outdoor type is ventilation. Both natural gas and propane tankless hot water heaters need ventilation facilities to let out gas for safety when installing indoor. However, if you get it hooked outside, no ventilation is needed and much money is saved on it.

What Size Tankless Water Heater Do You Need for Indoor Use

There is hardly a one-dimensional answer to this. That is because different businesses have different needs. Remember, you will always need a steady supply of hot water for your home, and having the right size will matter. Such will be the time for you to observe the following variables. This way, you will find the perfect size for your tankless water heater.

• Check the number of units you need

Understanding the number of devices you need in your home space will ensure that you get the right flow rate. Usually, you will have to add the flow rates required by each device in your building. Once you get the total, you will be sure of what GPM rating your tankless water heater should have. For instance, if your total flow rate is 7.1, a GPM rating of 7.5 will come in handy.

• Check the temperature rise

It will be best for you to focus on a relatively lower temperature rise. Assuming that the incoming water temperature is 60 degrees, your water heater should be around 105 to 110 degrees. This way, the temperature will take a relatively short time to get to the desired level. The larger the temperature provided per GPM, the better the device will be to you.

• Put it all together

Once you are conversant with how many units and temperature rise you need, put everything together. For instance, if you need a GPM of 7.5 and a temperature rise of 50 degrees, it will be easier for you to zero down on the most appropriate choices.

How to Install Indoor Tankless Water Heaters?

This process is relatively straightforward, but only if you consider the requirements. In most cases, you will need to pay attention to the vent pipes, the location of your source of power, available space, and the location of the most used water fixture.

Here are the steps you need to follow when installing your device.

• Preparation

Take the time to understand the various safety measures you need to undertake. Ensure that there is enough power supply, whether from gas or electricity. But beyond this, there needs to be no leakage of the same.

• Install new gas and water lines

Such will be the time to install a tee or a valve in your gas line. Ensure that it is as flexible as possible. The water lines will also need to be fixed accordingly. Usually, you will have to separate the hot and cold lines during this time.

• Install the water heater

Next, you will need to switch off both the water and power lines before starting the installation process. Ensure that the installation is not flush to the wall, which will improve efficiency levels in the long run.

• Connect the water heater

This process varies from one brand to another. For this reason, ensure that you pay attention to what the manufacturer has provided. The last step will be installing your vent.

• Switch the power on

Now is the right time to test your water heater.


1. Can indoor tankless water heater be installed outdoor?

It depends, if there is a clear remark on the products for outdoor installation, then you can hook it up outside. Or it needs to be installed indoor only. You can ask the manufacturer for sure before and after buying.

2. Do all the indoor tankless water heaters need ventilation facilities?

No, only natural gas and propane tankless hot water heaters need to install venting kits, the electric tankless water heater does not need.


Indoor tankless water heaters have many types and applications, all above top 9 best indoor tankless water heaters we recommended for you have their own advantages and shortcomings, you can choose according to your basic needs and budget.

To sum up, we picked out the top 3 best indoor tankless water heaters for different needs as follow:

Tankless Water Heater Best Type
Best whole house type Rinnai RUC98iN Tankless Water Heater
Best one for middle size home use Rinnai V65IN 6.6 GPM Tankless Water Heater
Best electric type Stiebel Eltron Tempra Plus 24 kW Tankless Water Heater

If you have an interest in the item and would like to get more information on the products, please check out freely on Amazon. There will always be a large discount on Amazon, so you can save a large sum of money in purchasing. If you still have any other problem in selecting the best suitable one, you can just contact us for more.


Will Montgomery

Will Montgomery: Electro-Mechanical Engineer, Serial Entrepreneur, and Real Estate Enthusiast. Met David at Penn State, where he earned a BS in Electro-Mechanical Engineering and a minor in Business. Expertly manages capital equipment manufacturing, refurbishing, and repair businesses, while exploring opportunities in real estate and advocating for practical heating solutions.

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