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Rinnai RL75iN Natural Gas Tankless Water Heater Review

Water Heater Review

The Rinnai RL75iN Tankless Water Heater is a non-condensing indoor model. It's packed full of standard and optional features and performs at an exceptional level. You'll find all the bells and whistles you'd expect from a water heater manufacturered by a leader in the tankless water heater industry.

This review will give you a deep dive into this popular gas tankless water heater and help you decide if the Rinnai RL75iN is the right purchase for your home. However, if you're looking for an outdoor model, Rinnai manufactures the exact same unit designed for outdoor installaion (RL75eN).

Rinnai RL75iN Tankless Water Heater Review


  • Isolation Valves - Isolation valves are included to help you perform maintenance. 
  • Scale Detection - When it's time to flush your tankless due to lime scale build-up, you'll be alerted by the scale detection feature.
  • Temperature Lock - Once you find the perfect temperature, you can set and lock it in place. 
  • High Altitude - This tankless will work in altitudes up to 10,200 feet.
  • Wi-Fi Enabled - The Rinnai Tankless RL75iN is wi-fi enabled so it can be used with the optional Control-R feature.
  • Control-R - Do you have a smart phone? You can connect your phone to Control-R and adjust the temperature from a remote location, receive alerts, and so much more. 
  • Remote Monitoring - Maintenance and repair alerts can be delivered to the dealer of your choice using Control-R. The dealer can monitor your tankless and Control-R will even send alerts directly to your smart phone.
  • Venting Options - The unit can be vented either horizontally or vertically, giving you the choice to vent either through the roof or a wall. 

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 degrees, 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 should definitely help you lower your 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.


If you're not into bells-and-whistles you'll probably be better served selecting a tankless water heater that's not wi-fi enabled. Why pay the additional expense if you're not planning to use the features?

But if you're looking for a tankless that can deliver a large amount of hot water with plenty of wi-fi remote monitoring options, the Rinnai RL75iN is a great choice.

Rinnai has designed an exceptional unit that's built to last. They even back it up with a 12-year warranty! The RL75iN falls into the higher-end of the price range when it comes to gas tankless water heaters, but the upgrades and features help make this 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. Their commitment to the tradition of constant improvement can be seen in ther exceptional 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 Rinnai RL75iN can fit into nearly any room. 

Venting Options

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 Rinnai 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 they include a set 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 the 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. Just think, your hot bath can be ready and waiting for you while your still downstairs!


Energy Efficiency

The term Efficiency Factor (EF) is used to measure the efficiency of water heaters. The RL75iN is rated with a .81 EF, which is a simple way of saying that 81% of the energy the water heater used was converted into heat.

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 rated models available. Rinnia's RU199iN is a Super High Efficiency Condensing Gas Tankless with an EF rating 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 DIY'er you should hang up your tool belt for this project. Installing a tankless water heater needs to 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 local and national codes will need to be followed. Find a licensed contractor who's 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, is user friendly, and is 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 great choice for large homes where the hot water demand can be high, and the unit is even certified for manufactured (mobile) homes!