Rinnai RUC Series Review

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Rinnai RUC series is the group of ultra efficient tankless water heaters that offers something unique; both concentric PP and dual-pipe PVC/CPVC venting options, on the same unit. The dual venting RUC models have been released in 2014 and provide great time saving and flexibility during the installation.

Models review

Rinnai RUC98i

Rinnai RUC water heaters RUC80i, RUC90i and RUC98i are coming from the Ultra direct vent group that are available in three sizes, all designed for the indoor installations in residential homes and mobile homes, and supplying hot water to the maximum of four bathrooms.

While the units are factory set to use the natural gas, they can be converted to use the propane gas too.

The Ultra series, except the tankless and on demand water heating capability, offers condensing technology for the ultra high energy efficiency and high water flow rate of maximum 9.8 GPM.

The RUC98i model has the most powerful burner that can generate up to 199,000 Btus, but also, due to the modulating gas burner, reduce its power to low 15,200 Btus. The water temperature, which is controlled by the temperature controller or dip switch, can be set to the maximum 140F, in residential applications, while in commercial, up to 185F. The temperature controller is built into the front panel while the additional controllers can also be installed. Except the temperature adjustments and control, the controller allows users to see other parameters, including the error codes for easy diagnostics during the failure.

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 adaptors 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 heat exchanger and 5 years on parts.


RUC80i RUC90i RUC98i
Gas Input
Water Flow
0.26-8.0 0.26-9.0 0.26-9.8
Energy Factor
0.96 0.96 0.95
Activation rate
0.4 0.4 0.4
Temp. settings
98-140 98-140 98-140
Electric consumption
75 75 75
Max. vent
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
10200 10200 10200
18.5x26x10 18.5x26x10 18.5x26x10
62 62 62


The best model from Rinnai RUC series is the largest RUC98i model due to the high energy factor, powerful 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, Eco-friendly technology with the environmental benefits and especially the venting options that allow flexible installation.

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(Photo credit to Rinnai)