Rinnai RU Water Heaters
Review & Buying Tips
(updated 2017)

Explore the benefits of the Rinnai RU water heaters utilizing the tankless and condensing technology; see the review of the top features and compare specs between the models. Compare Rinnai RU80, RU90, and RU98 to buy the best model for your home.

Enjoy all the comfort and high performance for less. Do you need plenty of hot water in endless supply for your new home, or as the retrofit, something that will replace an existing water heater?

Rinnai tankless water heaters from RU series, with the three sizes available RU80, RU90, and RU98, are capable meeting all your needs for hot water, saving you money for using less energy while protecting the environment with the reduced pollution.

Either you need hot water in the kitchen and/or bathroom of your small or large size home, even small commercial application - water heaters are powerful enough to deliver hot water up to 4 fixtures simultaneously, with less temperature fluctuation. Moreover, with the Wi-Fi connectivity and the smart-phone, the heating operation can be controlled and monitored remotely.

Models and features review

Small size for easy installation

All Rinnai RU water heaters are ventless and designed for the outdoor installation - great for the homeowners who are not comfortable having the gas connections inside the house.

The small size of 18.5" x 26" x 10" and weight of only 62 lbs, makes the units easy to handle and install - mainly on the outside wall, or in the recess box. Most of the features are the same, while the main differences are in the maximum power and water flow they can generate.

Rinnai RU water heaters - Differences

Rinnai RU water heatersRinnai RU

Rinnai RU80e, with the 152,000 Btu power output and flow rate of 8.0 GPM, is the smallest unit, recommended for homes with up to 2 showers.

Rinnai RU90e is designed for use in homes with up to 3 showers as its power output reaches 180,000 Btu and delivers up to 9.0 GPM of hot water.

Rinnai RU98e, with the gas burner generating up to 199,000 Btu, is the largest and most powerful unit in this group, easily supplying up to 9.8 GPM of hot water to the maximum of 4 fixtures simultaneously.

As can be seen from above, the maximum power is different between the RU models, but the minimum is the same -
15,200 Btu. This power fluctuation from its minimum to the maximum value depends on the water flow and is possible due to the modulating gas valve.

Dual heat exchangers

Rinnai RU water heaters come with the condensing technology that utilizes two heat exchangers; condensing heat exchanger that pre-heats the incoming cold water by using the heat from the flue gases, and the primary heat exchanger made of copper,  where the water is heated and from where it is delivered to the fixtures.

Due to the condensing technology, energy efficiency is much higher than in non-condensing type. Rinnai RU80 and Rinnai RU90 come with the highest energy factor of 0.96 while the model RU98e has the EF of 0.95, resulting in up to 40% energy savings - making them, depending on the home size, a good buy.


A digital temperature controller MC-91-2US comes as the standard feature and is used in residential and commercial applications. It allows users to choose the desired temperature between 98 F and 140 F. Higher temperatures of up to 185 F can be achieved if the commercial controller MCC-91 is installed (sold separately).

Feature highlights

  • Direct electronic ignition eliminates the need for the pilot light.
  • Environment-friendly and Ultra Low NOx burner that complies with the 20 ppm NOx emission levels.
  • Digital temperature controller MC-91-2US is used to monitor the temperature, adjust the settings and display the error codes for easy troubleshooting.
  • Improved detection of the lime-scale in the heat exchanger.
  • Built-in Rinnai Circ-Logic recirculation program that cycles an external pump for faster hot water delivery, better comfort, and higher efficiency.
  • Temperature lock feature that prevents accidental or unauthorized temperature changes.
  • Water flow sensor, electronic water control device and electronic by-pass control.
  • Safety features such as the flame and boiling protection, combustion fan check, remaining flame OHS, automatic frost protection (protects the unit when the outside temperature is up to -22 F).
  • The diagnostic system helps in service.
  • Wi-Fi ready for remote control.

Specifications - Technical data

Models / Specs RU80e RU90e RU98e
Gas input (BTU) 15,200-152,000 15,200-180,000 15,200-199,000
Water flow (GPM) 0.26-8.0 0.26-9.0 0.26-9.8
Energy factor 0.96 0.96 0.95
Activation rate (GPM) 0.4 0.4 0.4
Temp. settings (F) 98-140 (185) 98-140 (185) 98-140 (185)
Altitude height (ft) 10,200 10,200 10,200
Size (inch) 18.5 x 26 x 10 18.5 x 26 x 10 18.5 x 26 x 10
Weight (lbs) 62 62 62


Price of the Rinnai RU water heaters is between $1000, and $1500 and the installation is around $1000. According to the user reviews, RU water heaters are suitable replacement for the tank-type, improving savings and comfort of the household - no major complaints about the cold water sandwiches.

The warranty on all Rinnai RU water heaters is 12 years on the heat exchanger and when used in residential applications, 10 years if used in potable water and space heating, and 5 years in commercial applications.

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