Rinnai RUC98i Tankless Water Heater Review

In Brief: Review of Rinnai RUC98i

The Rinnai RUC98ii is a premium tankless water heater that only consumes energy as and when required. Asa result, using this heater provides an endless supply of hot water without wasting electricity or water. The recirculation system ensures that hot water is recirculated through your pipes. This also eliminates any waiting time, giving users instant hot water.

Rinnai Corporation is a Japanese multinational company based in Nagoya. It was established in 1920 and is known for manufacturing home heating appliances that are energy efficient. https://en.m.wikipedia.org/wiki/Rinnai

The Rinnai RUC98ii is one such energy-efficient tankless water heater with a maximum flow rate of 9.8 GPM. It runs on either natural gas or propane.

Key Specifications of Rinnai RUC98i

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

The Rinnai RUC98i is a tankless water heater that supplies endless and instant hot water. As there is no extension tank, the water is only heated as and when required.

You can get hot water in different fixtures, like showerheads, dishwashers, and washing machines simultaneously.

It uses up to 40% less energy, which reduces utility costs. This energy efficiency can also contribute to a favorable HERS rating and optimize LEED certification.

The copper heat exchangers work efficiently and are also quite durable. Their long life in addition to many recyclable parts helps Rinnai users waste less. As compared to many water heaters, this model has lesser CO2 emissions.

It is ENERGY STAR® qualified and has an energy factor of 0.96. This is the first and only tankless heater that gives an option between concentric polypropylene or dual-pipe PVC/CPVC venting.

The integrated recirculation pump and internal bypass line (RUR models) provide hot water faster. The included isolation valves also make maintenance and caretaking easy.

Here is the long list of specifications – 

Type of applianceCondensing
Continuous flow
Gas hot water system
OperationForced combustion
InstallationIndoors only
Minimum gas rate15200 BTU/h
Maximum gas rate199000 BTU/h
Input4.5-58.3 kWh
Appliance electrical inputAC 120 V - 60 Hz
Temperature controller electrical inpuDC 12 V
Normal electrical consumption64 W
Standby electrical consumption2 W
Anti-frost protection electrical consumption146 W
Max amperage with pump8 A
Max amperage without pump4 A
Max amperage fuse10 A
Ignition systemDirect electronic
Minimum flow rate0.26 GPM
Minimum activation flow rate0.4 GPM
Maximum flow rate9.8 GPM
Temperature range98° - 120° F
Approved gas typesNatural and propane
Energy factor0.95
Service connection size3/4" MNPT
Water supply pressure15 - 150 PSI
Water flow controlWater flow sensor
Electronic water control
And by-pass control
Isolation and pressure relief valvesHeavy-duty forged brass Webstone Isolator valves EXP E2
Safety devicesFlame failure rod
Boiling protection
Combustion fan rpm check
Over current gas fuse
Remaining flame (OHS)
Therm fuse
Automatic frost protection
External recirculation pump controlBuilt-in Rinnai Circ-LogicTM
Controller cableNon-polarized two-core cable
Minimum 22 AWG
Natural gas supply pressure range
4" WC - 10.5" WC
Propane gas supply pressure range8" WC - 13.5" WC

These heaters are equipped with optional wifi connectivity. This allows you to monitor and control settings remotely.

By linking it to your phone or device, you can access diagnostics, technical bulletins, and all other product-related information.

The different components of this heater are:

  • Concentric Vent Stack
  • Dual Pipe Vent Option
  • Burner & Gas Manifold
  • Primary Heat Exchanger
  • Secondary Heat Exchanger
  • Integrated Condensation Trap
  • Built-In Circulation Pump
  • Internal Bypass Line
  • Modulating Gas Valve
  • Built-In Surge Protector
  • PC Board

For more details about Rinnai water heaters, click here to view the brochure or check out this video:


Ease of Assembly and Installation

The Rinnai RUC98ii is easy to install but must be installed by a licensed professional. The person installing this heater must have the following skills:

  • Gas sizing.
  • Connecting gas lines, water lines, valves, and electricity.
  • Knowledge of applicable national, state, and local codes.
  • Installing venting through a wall or roof.
  • Training in the installation of tankless water heaters.
  • Training can be accessed on-line at www.trainingevents.rinnai.us

The installation process is explained through detailed steps in the owner’s manual. These instructions span over about 40 pages and are written in basic English. There are also labeled diagrams that help you identify components correctly.

The manual begins with all the safety measures to keep in mind before beginning. It is crucial to pay attention to this information for the safety of you and your device.

At the end of the manual, you will find details about diagnostic codes, required maintenance, replacement parts, and warranty. In case the installer could use some visual assistance as well.

Here is a useful installation video:


Ease of Usage

The basic operation of the Rinnai RUC98ii is simple and easy to understand. But at the same time, there are many safety instructions that one must follow for smooth functioning.

The owner’s manual mentions these instructions in very clear language and also explains why they are important. The user interface features a temperature display, two control buttons, a power button, and a priority button.

It also has two indicator lights: an in-use indicator and a priority indicator. The priority light indicates that this controller is controlling the temperature and that hot water is ready to be supplied.

The priority can only be changed if there is no hot water running. Long pressing the power button for 5 seconds when the heater is off will convert the units from Celsius to Fahrenheit and vice versa.

Warranty / Repairs

The Rinnai RUC98i comes with a standard limited warranty. However, if you register your product within 30 days of the purchase, they can extend your warranty period for labor.

The standard warranty covers any defects in materials or workmanship. This is only applicable if the product is installed and operated according to the specified instructions.

The warranty does not apply if the product is used in an application that uses chemically treated water. Make sure that the product serial number and manufacture date are not defaced as it will void the warranty.

In case of any problems, you can visit their website (www.rinnai.us), call at 1‐800‐621‐9419, or write to Rinnai at 103 International Drive, Peachtree City, Georgia 30269.

To learn more about their warranty policy, click here or visit www.rinnai.us/warranty

Customer Review Analysis

We examined many e-commerce websites and online forums to check what customers think of the Rinnai RUC98ii.

Buyers seem more than happy with their purchase and have given a high average rating of 4.4 stars. Out of over a hundred reviews, 87% have given ratings upwards of four stars.

Users are pleased with the endless supply of instant hot water that can be used from multiple fixtures simultaneously. This eliminates the need to prioritize household chores.

It’s also very useful when hosting guests.

As no energy is being used to heat or reheat tank water, this heater saves both energy and water. The lower carbon emissions make it better for the environment.

The compact body allows users to place it in unconventional locations like cabinets, under sinks, or even in the attic.

This saves a lot of precious space, unlike regular water heaters that come with large extension tanks.

The multiple venting options make this system one of a kind. The product brochure helps you pick which kind of venting suits you. It also has details about how much space is required for venting.

Almost all consumer reports only had good things to say about this water heater. The only negatives that we can point out are that it is quite expensive and is not as energy efficient as some competing products.


Pros/Cons of Rinnai RUC98ii

Through our analysis of several consumer reports and expert comments, we found the following pros and cons:


  • Tankless design
  • Saves energy and water
  • Instant endless hot water
  • Wifi connectivity
  • Compact body
  • Multiple venting options
  • Durable


  • Mid-level energy efficiency
  • Expensive


Recommended Accessories with Rinnai RUC98i

Customers who bought the Rinnai RUC98i also were interested in buying the following:

Condensing Vent Pipe Extension

Rinnai 224087PP, 10-Inch, White


Rinnai 224080PP, 39″

Rinnai 224080PP Vent Pipe Extension, 39', Chrome


Rinnai 804000074 Condensate Neutralizer

Rinnai 804000074 Neutralizer Kit, Chrome



Do I need to get a condensation trap kit?

No, the condensation trap is included in the system. It will be installed with the heater itself.

What is the twin-pipe? What size does the twin-pipe need to be?

A twin pipe lets air intake and air exhaust occur in a single pipe. It needs to be 3 inches.

What is the difference between the RUC98ii and RUC98ie?

The Rinnai RUC98ii is designed for indoor use and the RUC98ie for outdoor use.

Can the RUC98iIN be converted to use propane?

Yes, it can. But it is much easier to purchase the RUC98iIP instead.

What is the difference between concentric and PVC venting?

The concentric vent allows both the exhaust vent and the intake combustion air to pass through a standard roof or sidewall. The PVC venting is a standard two pipe furnace venting.

Our Recommendation

The Rinnai RUC98ii is an ideal water heater for residential and commercial spaces. It comes in a compact unit that doesn’t take up much space. The copper heat exchangers last for long and are energy efficient.

This is a good investment for people who need an endless supply of instant hot water in multiple fixtures. While expensive, it also has several features that make the use of this tankless heater quite luxurious.

If it fits in your budget, it makes for a good buy. The money saved on lower utility bills eventually compensates for the initial costs.

Last update on 2021-09-22 / Affiliate links / Images from Amazon Product Advertising API

Steven Johnson
About Steven Johnson

Steven is a young science graduate who loves to research and write on topics related to water. He contributes articles when he gets free time from his day job.

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