Best Indoor Gas Tankless Water Heater

There are altogether two ways of installation, one is an indoor installation, the other is outdoor installation. Indoor installation is the most common method and is frequently adopted for the residential tankless water heater.

Best Indoor Gas Tankless Water Heaters Reviews

There are many types of indoor gas tankless water heaters on the market of 2019. According to the usage, they can be divided into residential use, commercial use, point of use type and whole house type. We have made reviews for each of which mentioned above, you can check them out freely if you have an interest.

After making a detailed comparison, we finally picked the following 6 types and made the best indoor gas tankless water heaters reviews for you:

1. Navien NPE-180A Premium Condensing Tankless Gas Water Heater

best indoor tankless water heater
tankless water heater for a house


  • Built-in buffer tank and re-circulation pump

This indoor tankless gas hot water heater adopts exclusive ComfortFlow internal re-circulation pump and buffer tank to save water and reduce the time to get hot water. And you do not need to buy extra re-circulation pump.

  • 8.4 gallons of water flow

The flow rate of the indoor gas tankless water heater is 8.4 gallons per minute, perfect for two or three bathrooms used in warm areas, you can also use kitchen faucets the same time.

  • Condensing efficiency

Condensing technology is installed to recover the extra heat that would be lost in non-condensing types, it helps to reduce energy consumption and greenhouse gas emissions. And it provides up to 0.97 UEF or 0.99 EF, which is highly energy efficient.


  1. High flow rate
  2. Highly energy efficient
  3. Cascading Capability
  4. Commercial and residential use
  5. Low NOx design


Waiting time for hot water is a bit long

2. Noritz NR981-SV-NG Indoor-Outdoor Tankless Water Heater

best indoor tankless water heaters
best tankless water heater home use


  • 9.8 gallons flow rate

The flow rate range of the unit is 0.5-9.8 gallons per minute, which is really a high capacity indoor tankless gas water heater. It supports three bathroom and kitchen faucets in warm areas and two bathrooms in cold areas.

  • Low NOx design

It is designed as a low NOx type, so less gas is wasted in using period and it is more energy efficient.

  • 100-140 degrees F

The temperature range of the unit is 100 to 140 degrees F, perfectly for residential use. And there are nine heating options you can choose.

  • 12 years warranty

Noritz promises to keep 12 years warranty for its heating exchangers. And the excellent quality enables you to use it for a long period of time, the copper wall is designed based on commercial grade, thus no leakage occurs in using.


  1. Highly energy efficient
  2. Indoor and outdoor installation available both
  3. Can be used for high altitude
  4. Commercial grade copper wall
  5. Simple operation


Waiting time for hot water is quite long

3. Rinnai RUC98iN Ultra Series Tankless Water Heater

best tankless water heaters for home
best home tankless water heater


  • 9.8 gallons flow rate

Like Noritz indoor tankless gas water heater, the flow rate of this unit is also up to 9.8 gallons per minute, which can be used perfectly for whole home use and is the best choice for a large family or middle size family use.

  • 2 venting design

For venting kits, it gives two options for you. One is concentric PVC while the other is a twin pipe. You can choose one that fits your home best.

  • 0.95 thermal rating

The thermal rating of the unit reaches as high as 0.95, which is really a high energy efficient natural gas tankless water heater. It means nearly all the natural gas is used without waste.


  1. Commercial & residential use both
  2. Quiet working condition
  3. Endless hot water supply
  4. Perfect for whole home use
  5. Smart digital control panel


Need to get professional for installation

4. Takagi T-K4-IN-NG Indoor Tankless Natural Gas Water Heater

best tankless water heater for apartment
best residential tankless water heater


  • 8 gpm flow rate

Compared with most of recommended indoor gas tankless water heaters above, this unit has relatively low flow rate, reaching only 8 gallons per minute, but it is still able to support multiple bathrooms and kitchen faucets use simultaneously.

  • 99-167 degrees F

The temperature range of it is between 99 to 140 degrees F, suits the need for residential and even commercial use perfectly. But there are only 4 temperature settings that are available. With the remote control, the maximum temperature reaches even more than 167 degrees F.

  • Self-diagnostic system

With self-diagnostic system, the heater is able to protect itself. When it attains too much heat, the light shows off and it stops working automatically.


  1. Large power consumption
  2. Both indoor and outdoor installation
  3. Smart internal freeze protection
  4. Remote temperature control
  5. Commercial use available


You need to buy extra remote controller for remote control system

5. Eccotemp FVI-12 Natural Gas Tankless Water Heater

residential tankless water heater reviews
indoor tankless water heater reviews


  • 3.6 gpm flow rate

This unit is a small flow rate of indoor gas tankless water heater, it is perfect for small or tiny home use. Able to support one bathroom and one kitchen faucet the same time.

  • Fast heating time

As a natural gas tankless water heater, the heating time is pretty fast. And it takes about only 5 seconds for hot water to flow, which saves much cold water and also saves a large amount of water bills for you.

  • Easy operation

There are clear and easy operated digital control, water temperature shows on for you to adjust. And two buttons are set for adjusting both gas and water temperatures.


  1. Easy installation
  2. Perfect for tiny or small house use
  3. Short waiting time for hot water
  4. Easy to operate
  5. Compact shape


Hard to get temperature accurately that you want

6. Navien NPE-240S-NG Premium Condensing Tankless Gas Water Heater

indoor propane tankless water heater
top rated indoor tankless water heater


  • 11.2 gpm flow rate

Among all the recommended best residential tankless gas water heater, this is the largest one on flow rate. It is capable of supporting 4 bathrooms and multiple kitchen faucets at the same time. And it can also be used for a commercial tankless heater.

  • 0.96 thermal efficient

The energy efficiency of the unit reaches 0.96, and the maximum input is 199900 BTU per hour. It helps to save a large amount of money on heating bills for you.

  • Preheating system

As one of the modern tankless water heaters, this is designed with the preheating system, it can smartly preheat for you if you use the hot water in regular time each day, and hot water maintains for a long period of time.


  1. Ultra condensing efficiency
  2. Endless hot water supply
  3. Digital control panel
  4. Smart design
  5. High energy efficient


A bit large on size compared with other types

The above six best indoor gas tankless water heaters are all in excellent working performance, you can check the prices on Amazon if you have interest.

Features Of Tankless Water Heater Gas Indoor

1. Short waiting time

According to the working principle of gas tankless water heater, hot water needs to flow through the pipe and then you can use it for bathing or washing in the kitchen. If you install the natural gas tankless water heater outdoor, then it takes quite a long time for hot water to flow to destinations. Thus the waiting time for hot water is prolonged, and it means more cold water is wasted, your water bill will be added accordingly.

2. Long using time

When you install the tankless water heater outdoor, it is easily broken with the wind or rain unless you add particular protection cover on it. However, indoor gas water heater absolutely reduces the matter, the machine will not be corroded by severe weather and thus the using time can be longer than outdoor gas tankless water heaters.

3. Easy installation

For indoor gas tankless water heater, the installation is quite easier than an outdoor one. And thanks to the simple design of most tankless water heaters, some of which can even be installed totally by oneself, and takes about only 2 hours to hook them up.

best indoor tankless water heater gas
indoor tankless gas water heater reviews

How To Choose Best Indoor Gas Tankless Water Heater

Gas tankless water heater adopts natural gas as its main power source, therefore, there needs to be a venting system for safety. Not only for the venting, but there are also many other things you need to consider in choosing and buying the best indoor gas tankless water heater,
here we will give you some tips on choosing:

1. Venting

As we have said, venting kits are the most important factor you need to consider. For some indoor gas tankless water heaters, the venting method is special and needs to be bought along with the machine. Besides, most residential 1/2 inch PVC pipe may not suitable for the venting kits, and they may require 3/4 inch ones. In order to reduce installation and using costs as much as possible, you should ask the manufacturer clearly about the venting requirements before buying.

2. Installation place

Some of the indoor gas tankless water heaters is a point of use types, while others may be the whole house types. Before buying, you need to make sure where you intend to install it, and if you want to get a whole home gas tankless water heater, or just want to install a small one for kitchen sink use.

3. Size

Though compared with tank water heaters, the tankless gas indoor water heater is much smaller. But the size of them still differs a lot. If you want a whole home tankless gas water heater, you may need a large size one. And for kitchen faucet only, portable and point of use tankless water heater may be more suitable.

4. Flow rate

The flow rate of each tankless water heater gas indoor can be various a lot, ranging from 3 gpm to perhaps 13 gpm. Mostly for residential tankless water heaters, the flow rate from 6-9 gallons per minutes can well suit multiple bathrooms use. So thinking about the actual flow rate you need before buying and choose the most suitable one.

Top 3  Best Indoor Gas Tankless Water Heaters

Tankless Water Heater Best Type
Noritz NR981-SV-NG Tankless Water Heater Best large capacity type
Rinnai RUC98iN Tankless Water Heater Best one for large family use
Eccotemp FVI-12 Natural Gas Tankless Water Heater Best one for tiny home use

If you still have any other trouble in choosing the best indoor gas tankless water heater or want to get more detailed information on products, please feel free to contact us or to check on Amazon directly.