Rinnai RUC98iN Natural Gas Tankless Water Heater


The Rinnai RUC98iN is an excellent tankless water heater (natural gas) with an innovative design and many desirable attributes that will save you space, money, and time. The product is easy to install using both twin pipe and concentric venting options (PVC). You do not need an adapter for the product to work. It also has an internal bypass line and an integrated recirculation pump that deliver hot water quickly and a power-efficient design that uses less energy at home. The heater saves money in the end.

Rinnai RUC98iN Ultra Series Indoor Natural Gas Tankless Water Heater, Twin Pipe
Provides an endless supply of hot water, on-demand ().
Rinnai RUC98iN Ultra Series Indoor Natural Gas Tankless Water Heater, Twin Pipe

In this article, we have reviewed some of the benefits and features of using the Rinnai RUC98iN. We have also explored how the best tankless water heaters work and how to choose the best size for your office or home.

Introduction | Rinnai RUC98iN

What type of water heater do you have at home? You probably own an old and worn-out model that has been in the bathroom since you were a teen. Moreover, it probably has a tank that takes up a lot of floor space at home. Do not bother to fix such a product as it will cost you a lot of cash.

Condensing, Temp controlled, Tankless, continuous flow, gas hot water system.

Rinnai RUC98iN
Use Propane or Natural gas.
Rinnai RUC98iN

If you are building or renovating a home, take advantage of the advanced technology in the 21st century. Tankless water heaters, for instance, such as Rinnai RUC98iN, are in demand for many reasons. Before we check out its features, let us look at how these products work.

Features of the Rinnai Ultra Series:

  • Energy Factor of up to 0.96 — ENERGY STAR qualified.
  • Comes in 199,000, 180,000, 160,000,130,000, and 152,000 BTU.
  • Supports dual-pipe PVC/CPVC and Concentric Polypropylene venting that boosts its flexibility. It supports multiple applications.
  • Has an internal bypass line RUR models) and an integrated recirculation pump that provides hot water faster than other brands. However, the product does not have a dedicated return line.
  • Has isolation valves that ease its maintenance.

How A Tankless Water Heater Works

A tankless water heater is an innovative household accessory that provides hot water on demand. Therefore, unlike in the past when water heater took a lot of space and used a lot of power, this innovative technology has changed things for the better. It does not require a reservoir for hot water, unlike traditional models. All you need is a compatible pipe and optimal water pressure to get warm water on demand during the day and at night.

Commonly referred to as ‘on-demand’ water heaters, these products can use either natural gas or propane to work. They do not need water tanks not to store warm water in a reservoir and switch from warm to cold water in seconds. As such, a new model will make your bath experience fun.

The Main Benefits of Tankless Water Heaters

We already know that all tankless water heaters do not require a tank and can heat up and deliver water in seconds in most settings. Models such as Rinnai RUC98iN offers other benefits to homes, key among them including:

  • It Will Save You a Lot of Space at Home
  • It Will Save You a Lot of Money Every Year
  • Supplies Hot Water Continuously
  • Safe for The Environment
  • Lasts for Many Decades
  • Innovative Self-Diagnostic System
  • Provides Cleaner Water

You Will Have More Space at Home

If you replace your water heater with a premium tankless model, the first change you will notice is that you have a lot of free space. Unlike old models that held around 50 gallons of water even when they were not in use, this one is different. It delivers hot water on demand, hence its name – tankless. The system uses a high-powered electric burner to heat water.

Overview Video on the Rinnai Ultra Series Tankless Water Heater

Compared to old-fashioned, tanked water heaters, tankless water heaters take up little space at home. Therefore, apart from saving valuable space, your home or bath area will look pleasing to the eye, as tankless water heaters are charming as well. You will love the value of the item offered.

Will Save You Money Every Year

Most tanked water systems have bulky, 50-gallon systems that take up a lot of valuable indoor space. Do you know how much energy such systems need to keep the water warm and ready to use? It is astronomical. After boiling water, it keeps it at a constant temperature until you switch it off.

This is not the case with the best tankless water heaters. Most modern systems use approximately 40% less energy to heat water on demand. While it is hard to estimate yearly cost-savings while using one, it is approximately 30-40% compared to the traditional, tanked water heaters.

Video | Rinnai Tanked vs Tankless Water Heater

Supplies Hot Water Continuously

How long does it take your tank to heat water once you switch on the power? You probably must wait for more than 10 minutes for the water to heat to an optimal temperature for bathing. Moreover, even though a 50-gallon water tank is a respectable size, it might not satisfy the needs of your family when everybody preparing for work/school in the morning.

The experience will be even worse if you have a household member who likes to hog water in the morning. Two or more of your household members will miss hot bath water in the morning, sparking conflict. However, thanks to tankless water heaters such as Rinnai RUC98iN, you will get as much hot water as you need at home for as long as you want.

Much Better for The Environment

Because of their efficacy, the best tankless water heaters are friendly to the environment. Therefore, whether you believe in global warming or not, it is good to ditch your tanked system as you will be contributing to social good in one way or the other. You will also save time and water as well.

The Rinnai RUC98iN, like comparable tankless water heaters, have low NOx emissions. Some models also have efficient systems that lower water wastage and therefore save their users a lot of money throughout the year.

Video | Learn More about Rinnai Tankless Water Heater

You can find the Rinnai RUC98iN at Amazon.

It Will Serve You for Longer

If you are using a tanked water heater at home, I bet it is old by now and has undergone multiple repairs before. I also guess that you have had flooded floors occasionally and have a cold shower once or twice per week because of a broken-down water heater. This is never the case with a tankless water heater. A new and well-engineered model lasts for decades.

Apart from lasting for decades, you will never worry about a tankless water heater breaking down often or requiring costly repairs. Most brands have heavy-duty products that last for decades. If you buy an original one and install it as directed, you have peace of mind using its daily for years.

Modernised Self-Diagnostic System

Like all other household accessories, the best tankless water heaters break down at some point. Fortunately, because they have a modernized self-diagnostic system, they tell you when the system has issues so that you can correct it to restore normal function. As such, they are cheaper to fix.

I bet that you have never owned nor used a tanked water heater that told you what is wrong with it. This is among many reasons why tankless water heaters are revolutionary. Whenever you suspect that it is not working well, all you do is check the control panel mounted on the front of the unit. Whenever there is an issue, the system will generate a code that you can look up in the manual to identify the fault. The process is very easy.

Provides Cleaner Water

With a tanked water system, you cannot monitor the quality of water in tanks as they often have a secure seal. However, if you can imagine water sitting in a barrel for years, you can imagine how nasty it probably is. The walls and the bottom of tanks build up dirt and grime over the years, which they eject slowly with water. With a tankless system, these are non-issues.

Unless you or other family members bathe every few minutes every day, water sits in tanks for more than eight hours every day. Thus, if the tank is old or made from rusty metal, you will have rust floating around your water, which is a health and safety hazard as well. The hot water from tankless water systems, or on-demand systems, does not sit in rusty tanks.

Rinnai Ultra Series Tankless Water Heaters

The Rinnai Ultra Series tankless water heaters are among the best in this niche. While they differ in terms of design and functionality, they have one thing in common – they deliver excellent results in most settings. The weight and dimensions vary slightly, while the power is heart-stopping.

Either of the units in this series not only generates hot water efficiently but also disperse water evenly throughout homes to offer a soothing bath experience. Understanding the operation of these products is not as easy as some people think – you need to understand some basic math. I will review the details later but you should understand one thing. Buy a product that you will not only enjoy using but will serve you well for years.

Rinnai RUC98iN Ultra Series Indoor Natural Gas Tankless Water Heater
Supports dual-pipe PVC / CPVC or Concentric Polypropylene venting.
Rinnai RUC98iN Ultra Series Indoor Natural Gas Tankless Water Heater

How to Determine the Size of Tankless Water Heaters

Please wear your Albert Einstein hat now as the road is about to get very bumpy. Before we explain how you can determine the size of your tankless water heater, you should understand these two broad things:

Working Out the Starting Water Temperature

Let us crunch a few basic numbers. Let us assume that you have checked and determined that the temperature of the groundwater of your home is 50 degrees using a thermometer or state wide average temperature data.

If this is the case, if you want the water from your kitchen’s tap whenever you are cleaning clothes or dishes to be 120 degrees, you will need a tankless heater that can raise water temperature by 70 degrees (120-50=70).

Calculate Water Flow Rate Needed

Your water faucets should have an optimal water flow rate to keep your home working well. Here is a quick example of how to calculate this:

  • The shower Flow Rate should be 1-2 GPM.
  • Washing Machine Flow Rate should be 1.5-3 GPM.

If you want to divert water to both systems at the same time, you will need 2.5-5 GPM water pressure for the system to work.

To get an accurate output, add these GPM ratings of all systems that you use at the same time at home to determine the total amount.

Putting Everything Together | BTU Needs

We are reviewing the Rinnai RUC98iN, so we will use it as an example in this case. Most tankless water heaters require around 200,000 BTUs to heat water to 50 degrees at a flow rate of 7.4 GPM. At this rate, you can provide hot water to most average household accessories without issues.

Generally, look for a product that can heat water by 10 degrees for every one gallon of water that flows through it per minute. As such, if you switch off a shower and its GPM falls to 6.4, the system can raise the temperature of water by 60 degrees. If water drops to 5.4 GMP (which is still high), the system should be able to raise the temperature of water by about 70 degrees. The rate often depends on the starting water temperature of your faucets.

The Rinnai RUC98iN is a commercial-grade water heater with a maximum output of 140 degrees. This is hot enough to melt off the skin.

To work out the exact size of the tankless water heater that you will need, you should factor in attributes such as the number of appliances that will you have at home and the efficacy of the tankless water heater you will need. For the best results, look for a premium item that you can afford to buy.

Rinnai RUC98iN | Propane Gas Tankless Water Heater

Rinnai RUC98iN | Propane Gas Tankless Water Heater
Internal parts of a Rinnai tankless water heater.
Rinnai RUC98iN | Propane Gas Tankless Water Heater


  • Dimensions: 5x26x10 inches (WxHxD).
  • Weight: 61.7 pounds.
  • Installation: Residential, Indoor, and Commercial.
  • Energy Factor: 0.95 for Propane and Gas.
  • Temperature Range
    • Residential: 98–140 degrees Fahrenheit (pre-set at 120°F) (including an MC-91-2US controller).
    • Commercial: 98–185 degrees Fahrenheit (with MCC-91-2US controller, sold separately).
  • Ultra-Low NOx: Yes.
  • Minimum Activation Rate: 0.4 GPM.
  • Flow Rate: 5 at 70 degrees Fahrenheit and 7.7 at 50 degrees Fahrenheit.
  • Hot Water Flow Rate Range: 26–9.8 GPM.
  • Approved Gas Types: Propane and Natural gas.
  • Min/Max Gas Rate (Input BTUs): 15,200 – 199,000 for natural gas.
  • Venting Options: Concentric PP/PVC.
  • Controllers
    • MC-91-2US (provided).
    • MCC-91-2US (optional for hydroponic and Commercial Applications).
    • MC-100V-1US Deluxe Controller (optional).
    • BC-100V-1US Bathroom Controller (optional).

Documents for the Rinnai RUC98iN:

Overview | Rinnai RUC98iN

As we have mentioned earlier, the Rinnai RUC98iN is the sole tankless water heater in the Ultra Series. We have identified other notable brands that you can use if this worthy product does not work for you.

This product can satisfy the needs of most families, which is why we have focused on it today. We will review the most desirable features and provide an Amazon link where you can read more about the product and order an original one if you want. The quality of the product is amazing.

  • Maximum output of 199,000 BTU
  • Respectable Temperature Range
  • Efficient Water Heater
  • Supports PVC and Concentric Venting
  • Water Flow Rate is Amazing
  • Compact Tankless Water Heater
  • Parts are Effortless to Change

Provides 199,000 BTUs of Power

The Rinnai RUC98iN has a BTU range of around 15,200-199,000, making it one of the best products in this niche. It is not only powerful but also designed to work seamlessly in most homes. In other words, you are getting a valuable tankless water heater that will satisfy your needs without costing you a lot of money. It is one of the best products in this niche.

Rinnai RUC98iN
Respectable Temperature Range
Rinnai RUC98iN

Your heater will reach temperatures of between 98-140F, which is more than you will ever need at home. You can pair it with a commercial remote and operate the system remotely whenever you need hot water for a bath or cleaning. You can also adjust the temperature (up to 185F) in a residential or commercial setting without touching the water heater.

It is The Most Efficient Heater

This tankless water heater has an energy factor of around 0.96 whether you are using natural gas or propane. Therefore, unlike standard electric heaters that are wasteful, you will enjoy unbelievable savings every month with this product. In the standby mode, for instance, it uses only 2 watts instead of the usual 64 watts, translating to significant cost savings. This increases to 140 watts in winter, as the Rinnai RUC98iN protects the system from freezing. It also has an Energy Star certified design with low Nox emissions, which makes the system 100% safe for the environment.

Rinnai RUC98iN Dedicated Mode Diagram

Rinnai RUC98iN Dedicated Mode Diagram
Supports PVC and Concentric Venting Options.
Rinnai RUC98iN Dedicated Mode Diagram

Most manufacturers of tankless water heaters do not offer versatile venting options, unlike the Rinnai. With an Ultra Series heaters water heater, you get both PVC and concentric venting options, which is amazing. The flexibility is important because it not only brings down operation costs but also enables the device to satisfy the needs of most people. While buying this heater, you will never worry about venting as its system supports both.

High Maximum Water Flow Rate

While installing a tankless water system at home, make sure that you are getting warm water on demand at an optimal flow rate. If the flow rate of water is low, you will have a hard time cleaning or bathing as water will trickle from your faucets at a snail’s pace. With the Rinnai RUC98iN, you get around 0.26 to 9.8 gallons per minute (GPM). Therefore, taking the maximum output into account, you get one of the most powerful tankless water heaters around. It can provide water to most rooms/areas seamlessly.

Compact Tankless Water Heater

Most tankless water heaters shine in this regard but the Rinnai RUC98iN model goes a step further. You can install one almost anywhere in your home, including in crawl spaces and attics, without cluttering personal space. The unit measures only 26 x 18.5 x 10 inches, which is almost the size of a small suitcase. It weighs around 80 pounds and therefore works well on most walls, including concrete and wood. Finally, you receive a separate remote that you can use to control its system from a distance.


You Can Change its Parts Effortlessly

Before we delve into the details of this water heater, let us check out what its warranty is about. For each original model that you order, you receive a 12-year warranty on the exchanger, a five-year warranty on its parts, and a one-year labor warranty. The heater has heavy-duty parts that you can replace effortlessly when worn. Rinnai RUC98iN also has a small front-mounted self-diagnostic panel that you can use to monitor the function of this product. It tells you when a component is not working at its peak, necessitating a change or maintenance. The instruction manual is diverse.

Difference Between Indoor/Outdoor Water Heaters

Let us now check out a couple of top-rated tankless water heaters. We talk about their features, major benefits, and the major differences between the top-rated brands. Even though most models work seamlessly indoors, you can use them outdoors as well without major damage or safety issues.

  1. Effortless to Install
  2. Handling Highly Acidic Water
  3. Have Access to Large Volumes of Air
  4. Some Minor Points

Effortless to Install

The installation of tankless water heaters can be a major and costly job due to their venting requirements. Most available models are so efficient that heat rarely escapes from their vents. However, the installation in homes is a chore that requires professional skill. This is rarely the case outdoors as plumbing is easier. Nothing gets in your way unlike indoors where you must chip walls and maneuver long pipes in small spaces.

Handling Highly Acidic Water

While setting up a tankless water heater indoors, you must find a way of draining water that forms due to condensation. The water is acidic and therefore more prone to damaging tankless water systems if you allow it to flow back into your heater. The exhaust venting system of some of the best brands we have reviewed are short and thus less prone to developing condensation. Considering that the warranty of most tankless water systems does not cover damage caused by water venting, this is a bonus.

Have Access to Large Volumes of Air

You should understand that the tankless water heater in your home requires a lot of oxygen to burn cleanly. While installing one, make sure that flow is optimal, as incomplete combustion can lead to the product running “rich.” This can lead to wastage of gas and can be a health and safety hazard if you do not correct it adequately. While air circulation in most homes is optimal, it might not be good enough for the best tankless water heaters to work optimally. This is often the case for people with small tankless water heaters installed in confined spaces such as closets. Drilling holes on walls that can boost oxygen supply costs a lot of money.

Some Minor Points

Even though I do not want to focus more on the differences between these water heaters, as they are small, differences do exist. If you have an outdoor water heater, you will have more free space at home that you can use to install other equipment. For most people, apart from those living in tiny studio apartments in places such as Hong Kong, this is never a concern. If you have a normal size home, you will notice a negligible dip in space. Outdoor tankless heaters can withstand harsh elements as well. Thus, using an indoor model outdoors can shorten its life significantly.

Rheem Tankless Water Heater | RTG Series

We have reviewed some marvelous indoor tankless water heaters. If you need an outdoor model, so you might want to look at an outdoor one. We have reviewed two Rheem RTG Series models that will serve you well for many years. Like the Ultra Series devices, they are almost similar so we will only look at key differences to help you make the best decision.

Rheem RTG-95 XLN | Tankless Water Heater

Rheem RTG-95 XLN | Tankless Water Heater
Hot-start programming minimizes fluctuation of water temperature.
Rheem RTG-95 XLN | Tankless Water Heater


  • Maximum power output of 11,000-199,900 BTU.
  • 5 GPM raising water temperature by 35 degrees.
  • 4 GPM raising water temperature by 45 degrees.
  • Next Generation Burner Technology.
  • Low Activation Flow Rate: Under 0.45 GPM.
  • UMC-117 remote control and a thermostat wire measuring 10 feet.
  • Comes with an EZ-Link cable for connecting and using two tankless water heaters as one.
  • You can connect to six units via an Optional control board (MIC-6 manifold).
  • Exclusive! All Rheem models support 20-unit manifold installations via optional MICS-180 and MIC-180 manifold control assemblies.
  • Works in high altitude (up to 9,840 feet elevation) without a chip.
  • Has an Exclusive overheat film wrap (Guardian OFW).
  • GAMA third-party efficiency certified tankless water heaters.
  • Energy-saving design provides continuous hot water. It also saves a lot of space at home.
  • Premium electronic controls boost safety and power efficacy.
  • Self-diagnostic program.
  • A digital display shows maintenance codes and temperature settings.
  • Powerful electric blower.
  • 120-volt power cord (provided).
  • Low Nox, eco-friendly burners meet SCAQMD rule 1146 requirements.
  • Up to -30° F freeze protection.
  • 11,000 – 199,900 Maximum BTU.
  • Temperature Range of 85-140 degrees Fahrenheit.

Rheem Documents:

Rheem RTG-64 XLN | Tankless Water Heater

Rheem RTG-64 XLN | Tankless Water Heater
Mid-efficiency tankless water heaters (gas-powered) provide hot water continuously.
Rheem RTG-64 XLN | Tankless Water Heater


  • 11,000 to 150,000 Maximum BTU.
  • 4 GPM raising by 35 degrees water temperature.
  • 6 GPM raising by 45 degrees water temperature.
  • Next Generation Burner Technology.
  • Industry best 0.40 GPM Minimum Activation Flow Rate and 0.26 GPM Minimum Flow Rate.
  • Remote controlled (UMC-117) with a thermostat. Ten-foot wire offered.
  • EZ-Link cable available for high demand applications to connect two tankless units to operate as one.
  • Manifold up to 6 units with an optional MIC-6 manifold control board.
  • All Rheem models support 20 manifold installations via a MICS-180 and MIC-180 manifold control assembly.
  • Works at 9,840 feet elevation (high altitudes) above sea level without using a chip.
  • Overheat film wrap (Guardian OFW).
  • GAMA certified efficient.
  • Compact and energy-saving design that delivers how water continuously in most settings.
  • Intelligent electronic controls boost its safety and efficacy.
  • Innovative Self-Diagnostic System.
  • A digital display shows maintenance codes and temperature settings.
  • Powerful electric blower (built-in).
  • Has a power cord (120 volts).
  • Low Nox, eco-friendly burner meets the requirements of SCAQMD rule 1146.
  • freeze protection up to -30 degrees Fahrenheit.

Main Benefits of Rheem RTG Series

As you can see, the only difference between the two outdoor water heaters is their maximum power output (BTUs) and hot water flow that you will have at home (GPM). Here are the cool benefits they have in common:

  • Efficient Tankless Water Heaters
  • Water-Saving Setting (Exclusive)
  • Compatible with Low Flow Fixtures
  • Compatible with Most Recirculation Pump Kits
  • Effortless to Install and Diagnose
  • Multiple Exciting Technologies
  • Deals with The Cold

Highly Efficient Tankless Heaters

These two outdoor water heaters (tankless) are not as efficient as the Rinnai RUC98iN model that we have reviewed herein but come close. The RTG Series tankless water heaters have an energy factor of around 0.82. Both models have efficient copper heat exchangers and electronic controls, purposefully designed to boost their efficacy. Finally, these water heaters have multiple health benefits for the environment. Because of their low Nox emissions, they have a negligible impact on the ozone layer.

Exclusive Water Saving Setting

These heaters have a propensity to lower water pressure as they heat cold water to your preferred temperature. Therefore, unlike some wasteful models, these products can save you thousands of gallons of water every year, synonymous with a full swimming pool. This translates to significant cost savings, plus you will have a significant impact on the environment. Buy a new one for your home as it delivers good results.

Low Flow Fixture Compatible

If you have a large home with many homeowners who enjoy hot baths in the morning, a tanked water heater might not satisfy your needs. It is better to order a versatile tankless water heater such as RTG Series as they provide hot water consistently in homes and commercial areas. According to Rheem, they have the first low flow tankless water heater with a flow rate of around 0.26 GPM. The minimum activation flow rate is around 0.40 GPM, which is also very low. As such, if you have low flow water faucets at home, this is one of the best water heaters to use – it delivers.

Compatible with Most Recirculation Pump Kits

In this Ultra Series, one of the major differences between the RUR and RUV tankless water heaters is their recirculation technologies, which comes built-in. While the base technology of the two products (RUC and Rheem) are different, you should still expect multiple benefits with an RTG series water heater, as it is compatible with most recirculation pumps. Thus, whether you have a big or small home, you can set it to deliver hot water to all your faucets the moment that you turn them on.

Easy to Install and Diagnose

You can connect this unit to most 3/5-inch concentric venting without using an adapter. Furthermore, all models are compatible with ½-inch gas lines commonly found in homes. Even though we will not evaluate those figures in detail, they show that Rheem tankless water heaters are versatile items that are easy to install in most homes. Via self-diagnosis systems, they can detect electrical and mechanical problems in real-time. They also flashing LEDs that tell you when they need maintenance.

Many Exciting New Technologies

The RTG Series has multiple new technologies built into its system, but there are a few standout ones that might interest you. Do you sometimes get fluctuations in water temperature whenever you are bathing? The hot-start programming, recently introduced in this product stops this from happening. They also have an exclusive fil wrap that prevents overheating.

Dealing with The Cold Outside

Most of us have an idea of what can happen when a tankless water heater overheats. However, do you have an idea of what can happen when the water heater (tankless) in your home gets too cold? Both the Rheem RTG-64XLM and Rheem RTG-95XLM can withstand temperatures of up to 30 degrees below zero. They work well at altitudes above 8,400 feet where it is always cold, have an inbuilt thermostat that maintains optimal temperature, and come with a free digital remote control and a 10-foot wire that not only ease their set up but also their operation in all settings.

Rinnai RUC98iN Has More Advantages Than Cons

In general, you will enjoy more benefits with a tankless water heater compared to a tanked model. For instance, because of their compact designs, you will enjoy ample space-saving with one, which is beneficial to people with small homes. Moreover, due to their efficacy, you will enjoy significant cost savings over the years, which is better. If you are shopping for a new tankless water heater, you will have a harder time finding something better than the Rinnai RUC98iN tankless water heater, in the Ultra Series. Buy an original to get a durable product that works well.

Compare prices from different stores and buy one for your home, as it is one of the most popular to date. The customer reviews at Amazon are a testament to its popularity and the valuable service that it delivers. Read a few to have an idea of the type and the quality of the product on offer. Many people love its durability and ease of use. Its heavy-duty parts and compatibility with most homes have also earned it a lot of attention online.


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