Rinnai RUC Water Heaters

The Rinnai RUC series is the group of ultra-efficient and ultra-low NOx tankless water heaters that offer something unique; both concentric PP and dual-pipe PVC/CPVC venting options, on the same unit.

The dual venting RUC models were released in 2014 and provide great savings and flexibility during the installation. With the three models RUC80i, RUC90i, and RUC98i to choose from, the RUC series is very attractive to buy.

Models review

Rinnai RUCRinnai RUC
(photo: amazon)

Rinnai RUC80i, RUC90i, and RUC98i are Energy Star tankless and condensing water heaters coming from the Ultra RUC series - designed only for indoor installations in residential and mobile homes, also in light commercial applications.

The size of all three models is the same, but water flow rates are different, ranging from 8.0 to 9.8 GPM so that the RUC models can deliver sufficient hot water to homes with a maximum of four bathrooms and with temperatures of up to 140 F.

The RUC models, except the tankless and on-demand water heating capability, offer a dual heat exchanger system with the condensing technology, making the units ultra-efficient where the temperature of the exhaust gases is lower than on standard type, so the PVC/CPVC venting can be used.

Powerful and eco-friendly burner

Rinnai RUC98i (sold on amazon.com) comes with the most powerful burner generating up to 199,000 BTUs, but also, due to the modulating gas burner, can reduce its power to a low 15,200 BTU. The smallest model from this group, RUC80i, has the same minimum power, while the maximum power can reach up to 152,000 BTU, whose energy factor of 0.96 vs. 0.95 is slightly higher.

Temperature controller

The water temperature, which is controlled by the temperature controller or dip switch, can be set to the maximum of 140 F in residential applications, while in commercial, up to 185 F. The temperature controller is built into the front panel, while the additional controllers can also be installed for achieving higher temperatures, especially in commercial applications. Except for the temperature adjustments and control, the controller allows users to see other features, including the error codes, for easy diagnostics during the failure.

Recirculation capable

RUC models feature the Rinnai Circ-Logic that utilizes an external pump, making the recirculation possible with the fast hot water delivery.

Features review

  • Maximum energy factor of 0.96 and Energy Star compliance guarantees great savings and low greenhouse emission
  • Designed for both natural and propane gas
  • Flexible venting options with the direct venting using concentric PP and twin-pipe PVC/CPVC venting options
  • No venting adapters needed
  • Green technology for the ultra-low NOx emission
  • Circ-Logic compatible with an external pump for water recirculation and fast hot water delivery
  • Safety features include; flame rod, boiling protection, combustion fan rpm check, thermal fuse, frost protection, OHS, and over-current protection
  • Standard gas and water connections of 3/4"
  • Warranty; 12 years on the heat exchanger and 5 years on parts


Models / Specs RUC80i RUC90i RUC98i
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 98-140 98-140
Energy consumption (Watts) 75 75 75
Max. vent length (ft) 65' - Conc. PP 41' - Two pipe PP 100' - PVC/CPVC 65' - Conc. PP 41' - Two pipe PP 100' - PVC/CPVC 65' - Conc. PP 41' - Two pipe PP 100' - PVC/CPVC
Altitude height (ft) 10,200 10,200 10,200
Size (inch) 18.5 x 31 x 10 18.5 x 31 x 10 18.5 x 31 x 10
Weight (lbs) 62 62 62


The best model to buy from the Rinnai RUC series is the most powerful RUC98i model (sold on amazon) due to the high energy factor, strong gas burner, and great hot water flow delivery. What makes all the above models unique are not only the on-demand and endless supply of hot water, but the extremely high energy factor, compact and space-saving size, recirculation capability, Eco-friendly technology with the environmental benefits, and especially the venting options that allow flexible installation.

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