Review: Rinnai RL75iN Natural Gas Tankless Water Heater

Water Heater Review

The Rinnai RL75iN Tankless Water Heater is designed to be a top performer. It's part of the Rinnai Award Winning Luxury Series, which has proudly earned the Energy Star Certification. The RL75iN is a non-condensing indoor model, however, Rinnai manufactures the exact same unit designed for outdoor installaion (RL75eN).

Packed full of standard and optional features, this unit not only delivers exceptional performance, but also provides all the bells and whistles you'd expect from a leader in the tankless water heater industry. 

Rinnai RL75iN Tankless Water Heater Review


  • High Altitude - Works in altitudes up to 10,200 feet.
  • Isolation Valves - Isolation valves are included. 
  • Venting Options - The vent is located on the top. However, the unit can be vented either horizontally or vertically. This gives the homeowner the choice to vent either through the roof or a wall.
  • Control-R - This add-on feature allows the homeowner to make temperature adjustments remotely from a smart phone.
  • Wi-Fi Enabled - The Rinnai Tankless RL75iN is wi-fi enabled to be used with the optional Control-R feature.
  • Remote Monitoring - Select a dealer to monitor your tankless through Control-R, in addition, automatic maintenance alerts will be delivered directly to your smart phone.
  • Scale Detection - This feature will alert you when the unit needs to be flushed due to lime scale build-up.
  • Temperature Lock - Set and lock the temperature to prevent others from making adjustments.

Advantages of a Tankless Water Heater


The Rinnai RL75iN Tankless Water Heater is designed to be a top performer. With an incoming water temperature of 57 degreess, this unit is able to deliver a respectable 4.7 GPM (gallons per minute). And at it's peak performance, it can deliver 7.5 GPM!

Like all tankless water heaters, the flow rate (GPM) is affected by the incoming water temperature. But if you look at the chart below, you can see that even with a 75 degree temperature rise, the RL75iN can deliver a solid 4.0 GPM.

Rinnai GPM Flow Table

Under normal circumstances, the RL75iN should be able to service 3 showers. Making this an excellent choice for 2 or 3 bedroom households.

The standard maximum temperature is 140 degrees fahrenheit. However, if you're a fan of warmer water, you can install an MCC-91 controller, which will allow you to increase the temperature to a toasty 160 degrees.

Rinnai's RL75iN produces low levels of nitrogen oxide (NOx) and is Energy Star Certifiied. You should definitely see lower water and gas utility expenses over a tank-style water heater.


The Rinnai RL75iN Natural Gas Tankless Water Heater comes with a limited 12-year warranty on the heat exchanger, 5-year parts, and 1-year labor.

The unit must be installed by a licensed professional who has attended Rinnai Installation Training Classes. Read the full warranty HERE.


The Rinnai RL75iN isn't for everyone. To start with, many homeowners may not need the amount of hot water this unit can deliver, and if the nifty wi-fi remote monitoring and smart phone temperature adjustments don't appeal to you, there really isn't a reason to purchase a wi-fi enable tankless.

With that said, we think this is a fantastic unit which is manufactured by a reputible company thats been around for many years. When you see a manufacturer offer a 12-year warranty you can rest assured that the unit was built to last.

This may be a higher priced gas tankless water heater, but it's also loaded with features and upgrades. The RL75iN is capable of delivering a seemingly endless supply of hot water. If you're looking for a high-demand gas tankless, this is an excellent choice.

How a Tankless Works

Company Information

Founded in 1920 by Hidejiro Naito and Kanekichi Hayashi in Japan, Rinnai began as a pressurized oil cooking stove company. In 1964 the founders began applying their skills to water heating, and to date have over 30 million tankless water heaters installed worldwide!

Rinnai is considered to be one of the world's largest manufacturers of gas appliances. The company's headquarters are located in Japan, but they have over 100 branch and sales offices worldwide. Rinnai is committed to the tradition of constant improvement, and it shows in their products.


Compact Design

Designed to mount onto a wall, you'll free up significant floor space, and since it measures in at 14 x 9.3 x 23 inches, the Rinnia RL75iN can fit into nearly any room. ​

You won't be limited by venting when it comes to the installation location. This unit can be vented either through the roof or the wall, giving you plenty of options.

Digital Panel

The digital control panel is straight forward and easy to use. It even features an error code indicator which provides you with a specific code to help you troubleshoot a problem if something ever goes wrong.

Rinnai Control Panel

Install a  MCC-91 controller if you want to set the hot water temperature to 160 degrees, which is 20 degrees above the standard temperature setting. The MCC-91 controller is also a great option if you chose the outdoor Rinnia model, since it'll allow you to adjust the temperature from the comfort of inside your home.

Isolation Valves Included

Rinnai understands the importance of installing isolation valves and so they are included with the RL75iN. The task of flushing your tankless water heater is so much easier with isolation valves.

Rinnai MIVK-T-LW Matsui Plumbing Isolation Valve Kit,

Wi-Fi Enabled

There's plenty of bell-and-whistles on the RL75iN, and it all starts with wi-fi. Install an optional Control-R module and you'll be able to change the temperature from your phone, send dignostic issues to a service tech, and even see troubleshooting options.

Do you have Amazon Alexa installed in your home? The Rinnai RL75iN can be controlled by Alexa. Your hot bath can be waiting for you as you're climbing the stairs!


Energy Efficiency

An Efficiency Factor (EF) is used to measuring the efficiency of water heaters. The RL75iN is rated at .81 EF. This means that 81% of the energy used to heat the water is actually converted into heat. (wording) link to official page and quote.

A .81 EF rating isn't bad for a gas tankless water heater, especially when you consider a tank-style gas Energy Star model is usually in the .67 to .70 EF range.

Still, tankless water heaters have better rating models available. Rinnia's RU199iN is a Super High Efficiency Condensing Gas Tankless with an EF of .92. And of course, if you're really looking for stellar energy efficiency you should look into purchasing an electric tankless, such as the Stiebel Eltron Tempra Plus 36 which has an EF rating of .98!

Requires Professional Installation

If you're a DYI'er you should hang up your tool belt for this project. Installing a tankless water heater should be done by a professional, and Rinnia's units are no exception.

Gas, plumbing, electrical and venting will all be part of the installation, and addition, local and national codes will need to be followed. Find a licensed contractor who is trained by Rinnai to do the installation.

Not only will you have the peace of mind that the job was done right, but you can also rest assured that the warranty won't be compromised.

Final Thoughts

The Rinnai RL75iN is an excellent tankless water heater. It's packed full of features, user friendly, and designed to last (with the proper care, you could expect 20+ years of service). 

Rinnai makes superior products and the RL75iN Natural Gas Tankless Hot Water Heater is no exception. In fact, its one of the best available on the market in its class.

This is an excellent choice for large homes where the hot water demand can be high, and it's even certified for manufactured (mobile) homes!