Rinnai RUC98iN Ultra Series tankless water heater review

The Rinnai RUC98iN Ultra Series is a tankless water heater with a high flow rate and wide temperature range.

Rinnai RUC98iN Ultra Series tankless water heater review
(Image: © Amazon)

Top Ten Reviews Verdict

The Rinnai RUC98iN is a powerful tankless water heater with Energy Star certification. It is ideal for commercial use.


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    Energy Star certified

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    Concentric or PVC venting option

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    9.8 Gallons per Minute flow rate

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    12 year warranty on heat exchanger


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The Rinnai RUC98iN Ultra Series is one of the best tankless water heaters for residential and commercial applications. It uses propane or natural gas and has multiple venting options. The RUC98iN is 26 inches tall, 10 inches thick, and weighs 61.7 pounds. Although it is compact and has a sleek design, it is not a lightweight water heater. 

It has a gunmetal gray exterior with controls located on the lower lip of the front panel. These include a power button, water temperature and gas control buttons, and a digital display. Besides controlling the temperature of hot water coming out of the unit, you can lock the temperature button to prevent unauthorized access.

Rinnai RUC98iN Ultra Series: What you need to know

Venting options for the Rinnai RUC98iN include concentric or twin-pipe PVC. This heater also complies with nitrogen oxide emission standards. This unit has bigger gas and water supply inlets and outlets than most gas tankless water heaters. It uses an electric ignition system and draws only 2 watts in standby mode. However, while it is actively working, the Rinnai RUC98iN consumes 64 watts of electric power, and it requires up to 146 watts to keep its parts from freezing during winter.

The Rinnai RUC98iN is not only bigger and heavier than the most home tankless water heater brands, it is also more powerful. First, it has an energy factor of 0.95 whether you use it with natural gas or propane. This is higher than the average for gas-powered water heaters. It is also an Energy Star-certified heater.

Rinnai RUC98iN Ultra Series review

(Image credit: Getty)

Its minimum-to-maximum gas burn rate varies from 15,200 to 199,000 Btu, a very wide range. In addition, the heater's hot water flow rate range is also very wide at 0.26 to 9.8 gpm. Its minimum activation flow rate is only 0.4 gpm. These figures indicate that this Rinnai tankless water heater can power multiple faucets and showerheads and can be used in multi-bathroom households without interruption to hot water flow.

The standard model of the Rinnai RUC98iN is capable of heating water to temperatures of 95 to 140 degrees Fahrenheit. In fact, the commercial model can provide water as hot as 185 degrees Fahrenheit. However, this is an expensive water heater. It uses 0.75-inch MNPT water and gas connections rather than the regular 0.5-inch connections found in most homes. In addition, it is difficult to install and requires maintenance by certified Rinnai repair personnel so as not to void its warranty, though other manufacturers, such as EcoSmart and Rheem, have similar restrictions.

Should you buy the Rinnai RUC98iN Ultra Series? 

The Rinnai RUC98iN is a sleek and highly efficient gas tankless water heater that uses both natural gas and propane and comes with multiple venting options. However, it is bulky and can be tricky to install.

John Carlsen

John has been researching and reviewing home security and smart home products for Top Ten Reviews since 2013. As well as covering smart home and home security and safety, he also covers other home technology products such as HVAC, garage door openers and more. He enjoys DIY, writing and hiking in his spare time.