Rinnai RUC98iN Ultra Series Indoor Natural Gas Tankless Water Heater, Twin Pipe

Rinnai RUC98iN Ultra Series Natural Gas Tankless Water Heater

Note: This product was discontinued by the manufacturer. We recommend you checkout our updated reviews of the best tankless water heaters on the market today.

The Rinnai brand has led the charge when it comes to delivering superior technological innovation and reducing the size of tankless water heating systems, and the Rinnai RUC98iN Ultra Series Natural Gas Tankless Water Heater is no exception. Designed for both commercial and residential applications, this gas powered, indoor tankless water heater can use both propane and natural gas.

Although it features a sleek and compact design, the RUC98iN is not a lightweight. It measures 10 inches thick and 26 inches tall and weighs in at a hefty 61.7 pounds. The exterior has a gunmetal gray hue, and the controls are located on the front panel near the lower lip. The control panel features a power button, a digital display, and buttons for controlling the gas flow and water temperature. One unique feature of this control panel is that it has a button that allows you to lock the temperature, which prohibits unauthorized access.

Key Features

  • The Rinnai RUC98iN has a max BTU input of 199,000, making it particularly suitable for applications where a high temperature rise is required.
  • It has an Energy Factor rating of .96, which means that it is Energy Star certified.
  • An MC-91-2US controller is included in your purchase, which allows the user to control the water’s temperature remotely.


  • Rinnai offers a 12 year warranty on the heat exchanger, a five year warranty on components, and a one year warranty on service and labor.
  • The RUC98iN has two venting options: PVC or concentric.
  • Its compact design allows it to be installed almost anywhere in a home.
  • Advanced technology ensures that this model has ultra-low NOx emissions.


  • A small percentage of customers have had negative interactions with Rinnai’s customer service department.

    Product Review

    Right out of the box, the Rinnai RUC98iN makes an impression. It is heavier and bigger than most tankless water heaters, but it also offers significantly more in terms of power. Because it has an energy factor of .96, it can be used with either propane or natural gas. This EF rating is higher than the average gas powered tankless heater, and it is worth mentioning that this model is Energy Star certified as well.

    The RUC98iN offers multiple venting options, including twin pipe PVC and concentric. Even with these two venting options, no additional connectors are required. It also complies with all state and federal requirements for nitrogen oxide emission standards. When compared to similar models, it has larger water and gas supply inlets. When in standby mode, it only draws 2 watts of power; however, once it is fired up, it consumes an average of 64 watts of power. It can require up to 146 watts of power to prevent its components from freezing during the colder months of winter.

    The minimum to maximum burn rate for this model varies between 15,000 to 199,000 BTU, which is a wide range. The flow rate for this Rinnai model also ranges widely ““ from .26 to 9.8 gallons per minute; however, the minimum activation flow rate is a mere .4 gpm. These figures are representative of the thought and care that was put into the design of the RUC98iN. It can power multiple major appliances and showerheads at one time without having to worry about any disruption being made to the flow of hot water.

    The Rinnai RUC98iN Ultra Series Natural Gas Tankless Water Heater is available in two different models: residential and commercial. The residential model will heat water up to 140 degrees Fahrenheit; however, the commercial model is capable of heating water up to 185 degrees F. At the same time, this tankless water heater is an expensive one. Rather than using the standard .5 inch connections you would find in most houses, it requires a .75 inch MNPT gas and water connections. This may necessitate additional upgrades to a buyer’s home.


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    Moreover, the Rinnai RUC98iN has a reputation for being difficult to install. All installation and maintenance work must be conducted by certified Rinnai personnel, otherwise its warranty is voided. A small percentage of reviewers have experienced difficulty in reaching satisfactory solutions with Rinnai’s customer service department.

    Thank You For Reading

    The Rinnai RUC98iN Ultra Series Natural Gas Tankless Water Heater is one of the more powerful tankless water heaters on today’s market. It has a sleek appearance and offers a high level of efficiency. However, its design is bulky, and it can be difficult to install. With that said, at the time of this writing, 91% of reviewers that we found have rated this model four stars or higher. Coupled with Rinnai’s industry-leading warranty, this tankless water heater seems like a solid investment for your home.