Rinnai RU and RUC Tankless Water Heaters Review and Buying Tips

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A review of Rinnai RU and RUC tankless water heaters for residential water heating including the main characteristics and exclusive features for easier selection. Check out how flexible venting system allows fast and hassle-free installation of the indoor models and how high energy factor brings great savings to its owners.


Model review

Rinnai manufacturer offers three model sizes from the RU and RUC lines of Ultra series; RU designed for the outdoor and RUC series made for the indoor installation only:

  • Rinnai RU98e and RUC98i

  • Rinnai RU90e and RUC90i

  • Rinnai RU80e and RUC80i

Rinnai RU98e and RUC98i are the largest models that come with the power ranging from 15,200 BTU to high 199,000 BTU, thanks to the powerful modulating gas burner. The built-in gas burner is not only strong but is eco-friendly, due to its low NOx gas combustion. Water can be heated up to 140 F in residential applications and 180 F in commercial, and with the water flow rate of 9.8 GPM, these units can easily supply hot water to homes with up to 4 showers or fixtures.

Rinnai RUC98Rinnai RU90e and RUC90i are mid-size models that provide up to 180,000 BTU of power and water flow rate of 9.0 GPM, supplying hot water up to 4 fixtures simultaneously while keeping the reasonable comfort level.

The smallest outdoor RU80e and indoor RUC80i models are still coming with the great features, compact size, and ultra-high efficiency of 0.96, but the power is lower - 152,000 BTU and water flow rate of 6.0 GPM - supplying hot water up to 3 fixtures.


Great engineering

The above RU and RUC models are coming from the Ultra series, a series with the water heaters that incorporate a tankless and condensing design, heating and delivering hot water on demand and in an endless supply. And thanks to the condensing design and two heat exchangers, the efficiency is higher than the efficiency found on non-condensing models while the exhaust temperature is lower, allowing a wider selection of the vents.

Flexible venting system

Great flexibility in the venting system for Rinnai RUC series allows usage of the PVC, PP and CPVC pipes with the concentric and twin-pipe venting, which eliminates the need for the venting kit or adapters. Such an innovative direct vent design with the smaller and compact size is what makes installation faster while providing more options.

High water flow rate

Due to its high hot water flow rate of up to 9.8 GPM, the largest Rinnai RU and RUC models are able to deliver an endless supply of hot water up to four bathrooms at the same time and thanks to the modulating gas valve your comfort and set temperature is not disturbed - less "cold water sandwiching".


With the built-in Circ-Logic recirculation, Rinnai tankless water heaters are able to control the external circulation pump and deliver hot water as soon as there is a call, shortening delivery time while reducing the hot loss.


As it can be seen in the picture, the temperature controller is built into the front panel of the indoor models, while it is provided with the outdoor models. The control allows simple temperature setup, monitoring and easy troubleshooting with the error code display. For the commercial and hydronic applications that require higher temperatures and which cannot be achieved with the provided controller, a different type is available.

Part of the advanced features is the enhance scale detention system that helps in reducing the scale build-up inside the unit, resulting in consistently high efficient heating while protecting the unit from damages and shorter life.

Modern look

All the models from RU and RUC series have a modern metallic look which makes them ideal for the indoor installations due to the attractive look and outside due to the long-lasting casing. The warranty is long 12 years on the heat exchanger and 5 on other parts.

Safety elements

  • Flame rod - flame failure

  • Combustion fan rpm check

  • Boiling protection

  • Overcurrent glass fuse

  • Thermal fuse

  • Automatic frost protection

  • Remaining flame - OHS

Other important characteristics and specs

  • Maximum of 12-year limited warranty on the heat exchanger for residential water heating, 10 years for water and space heating and 5 years for commercial applications

  • Ultra low-NOx emission

  • Remote monitor and control using smart devices
  • Fully recyclable

  • Mobile home certified

  • Corrosion-free copper heat exchangers
  • High altitude operation - up to 10,200 ft

  • Maximum vent length up to 65 feet concentric type and up to 100 feet for 4" twin pipe PVC/CPVC

  • Gas line 3/4" and 1/2" gas line compatible

  • Water lines 3/4"
  • Hot water flow: 0.26 - 9.8 GPM maximum

  • Temperature: 98 F - 140 F (185 F)

  • Energy factor 0.95/0.96

  • Dimensions: 18.5" x 26" x 10"

  • Weight: 61.7 lb


Rinnai provides a 12-year warranty on the heat exchangers in residential applications and 5 years for the commercial use; 5 years on parts.

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Pictures - courtesy of Rinnai WH company

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