
The Rinnai RUC98iN is a fantastic natural gas tankless water heater that has a lot going for it, thanks to its innovative design meant to save homeowners time, money and space. Easy to install with both concentric and twin-pipe PVC venting options — no adapter required. Enables quick hot water due to the integrated re-circulation pump and internal bypass line and it’s energy efficient so it uses less energy, which ultimately saves you money in the long-run.
This article will discuss all of the features and benefits of the Rinnai RUC98iN as well as explain how a tankless water heater works as well as determining how to choose the right size.
Table of Contents...
- 1 Introduction | Rinnai RUC98iN
- 2 How A Tankless Water Heater Actually Works
- 3 The Main Benefits Of Tankless Water Heaters
- 4 How To Work Out The Size Of Tankless Water Heater You’ll Need
- 5 Rinnai RUC98iN | Propane Gas Tankless Water Heater
- 6 Difference Between Indoor And Outdoor Water Heaters
- 7 Rheem Tankless Water Heater | RTG Series
- 8 Rheem RTG-95 XLN | Tankless Water Heater
- 9 Rheem RTG-64 XLN | Tankless Water Heater
- 10 Rinnai RUC98iN Has More Pros Than Cons
Introduction | Rinnai RUC98iN
How old is the water heater inside your home now? It’s probably been there since the moment you walked in, and now it’s starting to look its age. If you’re having problems with your storage tank water heater it costs a lot of money to get it fixed, plus it’s even more expensive to have it replaced.
Condensing, Tankless, Temp controlled, continuous flow, gas hot water system

Maybe it’s time you started living in the 21st century by taking advantage of the new technology on offer. Everyone is going crazy over tankless water heaters like the Rinnai RUC98iN for a good reason. Before we look at the benefits of a tankless water heater let’s quickly touch on how they actually work.
Features of the Rinnai Ultra Series:
- Energy Factor of up to .96 — ENERGY STAR qualified
- Available in five sizes: 130,000,152,000, 160,000, 180,000 and 199,000 BTU.
- Allows for either Concentric Polypropylene or dual-pipe PVC/CPVC venting, providing the most venting flexibility in a single application of any manufacture.
- Faster hot water provided by integrated recirculation pump and internal bypass line (RUR models) with or without a dedicated return line.
- Easy maintenance is achieved with isolation valves.
How A Tankless Water Heater Actually Works
A tankless water heater will give you water on demand. There are lots of reasons why this is so great, but the way it works is the major selling point. A storage tank water heater like the one you own at the moment has to keep a huge amount of water inside a large tank, which it also needs to keep warm for when you’re ready to use it.
The ‘on demand’ water heater will only heat up the water when you’ve turned it on through a process using propane or natural gas, so it doesn’t actually store anything inside a tank. It can turn the water from cold to warm within seconds.
The Main Benefits Of Tankless Water Heaters
So you know there is no tank and it heats up the water when it’s needed, but why does this make the Rinnai RUC98iN and other tankless models so special? Here are the benefits you’ll walk away with if you decide to get one for your home.
- You’ll Have Much More Space Available
- Will Save You Lots Of Money Every Year
- A Continuous Supply Of Hot Water
- Much Better For The Environment
- It Will Last You A Lot Longer
- A Modern Self-Diagnostic System
- The Water Will Be A Lot Cleaner
You’ll Have Much More Space Available
The first thing you’ll notice straight away once you’ve installed a tankless water heater is the large amount of space you’ve now got. Water tanks might hold around 50 gallons of water, which will vary depending on how big the individual tank is. A tankless model simply heats water using a high-powered burner.
Overview Video from Rinnai | Ultra Series Tankless Water Heater
https://www.youtube.com/watch?v=xsmXByR9mU4
The actual unit looks tiny on your wall compared to the old fashioned way to keep water warm. Not only will you have more space in the place your tank currently resides, but I’m sure you’re not the only one who thinks they are a terrible eyesore. Tankless water heaters are as aesthetic as they are compact.
Will Save You Lots Of Money Every Year
We’ve just talked about how a storage tank water heater might hold around 50 gallons of water at any one time. Do you know how much energy it takes to keep that much water warm? After the water is heated up it’s got to keep it at the same temperature all the time unless it’s switched off.
Your new tankless model might only use around 40 percent as much energy to heat the water up on demand. It’s hard to estimate how much you’ll save each year because it will depend on how big your tank is and the tankless water heater you choose, but you’re easily looking at 30-40 percent savings.
Video | Rinnai Tankless vs Tank Water Heater
https://www.youtube.com/watch?v=kUIYrlk2QSg
A Continuous Supply Of Hot Water
Have you ever figured out how long it takes to heat up the water in your tank when it’s switched on? You’ll know because you’ve probably been unable to shower because of the cold water. A 50 gallon water tank might be a respectable size, but it’s still going to eventually run out if you have a large family trying to get ready in the morning.
It’s even worse when someone hogs the shower until the hot water runs out. Thanks to tankless models like the Rinnai RUC98iN heating up your water as needed, it’s impossible to ever get into a situation where you have to dive out of the shower because it turns to ice water.
Much Better For The Environment
Due to the fact it’s more efficient, it also means a tankless water heater will be a lot more friendly on the environment. We’re already seeing lots of problems on a daily basis whether you want to believe in global warming or not, so if every household was to ditch their tank it would make a difference.
The Rinnai RUC98iN and other top tankless water heaters also have extremely low NOx emissions. Some of them even have the power to reduce the flow of water to help you save a very large amount of it each year. It’s especially helpful in areas around the country where droughts can cause lots of trouble.
Video | Learn More about the Rinnai Tankless Water Heater
https://www.youtube.com/watch?v=2strDyBImXE
Buy the Rinnai RUC98iN from Amazon.
It Will Last You A Lot Longer
I know your tank has lasted a long time, but it’s nearly falling apart and you’ve probably had it repaired before. When was the last time you found water all over your floor or had to take cold showers for a week? A tankless water heater will last you decades until it finally needs to be replaced.
Lasting decades isn’t everything, because you also want to make sure it’s not going to break down as often. Your tankless model won’t have to be repaired as often because they’re designed to last. It doesn’t mean once it’s installed you can forget about it for 20 years, but you’ll waste less of your life dealing with issues.
A Modern Self-Diagnostic System
We can look in a bit more detail about what will happen if something does go wrong for some reason. A tankless water heater will have a modern self-diagnostic system. It will actually tell you what is wrong with it whenever you run into trouble, meaning it’s easier and cheaper to fix.
Have you ever seen an old water tank capable of telling you what is wrong with it? Whenever you suspect there is a problem you can look on the front of the unit. You’ll usually be given a code you can look up in your manual, plus if you need to call up about it you’ll know exactly what to say.
The Water Will Be A Lot Cleaner
Unfortunately you can’t see the inside of your water tank, but if you use your imagination it’s easy to imagine what it will look like. Do you really think the walls of the tank will be as fresh as the day it was installed, or will grime have slowly built up over the years? Hopefully you realize it’s got to be the latter.
Unless you’re in and out of the shower multiple times per day the water will have to sit in the tank for hours and hours. If it’s an old tank the traces of rust are going to be floating around, which doesn’t make it the safest thing in the world either. On demand water doesn’t even have a tank to sit in.
Rinnai Tankless Water Heaters | Ultra Series
The tankless water heaters in the Rinnai Ultra Series are all excellent, but they have one thing in common. They’re all more or less the same except for the size they come in. We’re not talking about the dimensions of the unit or the weight (which does vary slightly), but what it really boils down to is how much power you’ll need under the hood.
If the unit you buy will be able to let you have hot water throughout your home even if you have multiple things turned on at once. It’s not the easiest thing to understand because it requires some math, so I’m going to explain how it works but before I do you should know one thing. If you have the money it’s better to buy the best one you can afford.

How To Work Out The Size Of Tankless Water Heater You’ll Need
Put your Albert Einstein hat on because we’re about to go on a bumpy ride. Before getting to the explanation of how to determine your tankless water heater size requirements, you must first understand these 2 things to make the process easier:
Working Out Your Starting Water Temperature
Let’s keep the numbers basic, so you’ve checked and your ground water temperature is 50 degrees. You can use a thermometer to check, or there will be information online letting you know the average temperature in your state.
You want your kitchen tap water to be 120 degrees when you’re cleaning the dishes, therefore you’ll need a tankless water heater capable of increasing the temperature by 70 degrees (120 – 50 = 70).
Working Out Your Water Flow Rate Needs
All of your appliances should have the gallons per minute (GPM) of hot water you’ll need to keep them working smoothly, but here is a quick example to help you out:
- Shower Flow Rate = 1-2 GPM
- Washing Machine Flow Rate = 1.5-3 GPM
So if you wanted hot water diverted to both of those things at the same time you would need a total of 2.5-5 GPM.
Try to do this yourself by adding up the GPM ratings of all the things you might have running at once to figure out your total amount.
Putting Everything Together | BTU Needs
We’re about to focus on the Rinnai RUC98iN, so we’ll use that as the example in this scenario. A tankless water heater with 200,000 BTU will be able to heat water up 50 degrees if the GPM flow rate is sitting at 7.4. As you can see, it’s more than enough for the average household.
If we take things further you could say the temperature will be able to rise by 10 degrees for every 1 GPM we knock off. So if you switched off the shower and the GPM fell to 6.4 it would be able to raise the temperature by 60 degrees. Drop down to 5.4 GPM (which is still a lot) and you could raise the water temperature by 70 degrees.
This will really depend on your starting water temperature, because a tankless water heater can only raise the water temperature by so much, which is a maximum of 140 degrees on the Rinnai RUC98iN unless in a commercial environment. You only need the water so hot before it starts melting your skin off.
If you wanted to work out the exact size required you would need to know things like the total number of minutes appliances will be running for and the efficiency of the tankless heater, therefore if you’re not Matt Damon in Good Will Hunting go for the best one you can afford.
Rinnai RUC98iN | Propane Gas Tankless Water Heater

Features:
- Dimensions : Width: 18.5 Inches / Height: 26 Inches / Depth: 10 Inches
- Weight : 61.7 lbs
- Installation : Indoor, Residential and Commercial
- Energy Factor :0.95 for Gas and Propane
- Temperature Range
- Residential: 98°F–140°F (pre-set at 120°F) (with included MC-91-2US controller)
- Commercial: 98°F–185°F (with MCC-91-2US controller, must be purchased separately)
- Ultra Low NOx: Yes
- Minimum Activation Rate: .4 GPM
- Flow Rate: 5.5 at 70°F Temperature Rise / 7.7 at 50°F Temperature Rise
- Hot Water Flow Rate Range: 0.26 – 9.8 GPM
- Approved Gas Types: Natural Gas or Propane
- Min/Max Gas Rate (Input BTUs) : Natural Gas: 15,200 – 199,000
- Venting Options: PVC/Concentric PP
- Controllers
- MC-91-2US (included)
- MCC-91-2US (optional for commercial or Hydronic Applications)
- MC-100V-1US Deluxe Controller (optional)
- BC-100V-1US Bathroom Controller (optional)
Documents for the Rinnai RUC98iN :
- View or download the SPEC SHEET
- Vie or download the INSTALLATION MANUAL
Overview | Rinnai RUC98iN
As we mentioned a little earlier, the Rinnai RUC98iN is only one of the tankless water heaters in the Ultra Series. You also have a selection of others, so if the RUC98iN doesn’t suit your needs you can always choose one of the other models.
It’s probably going to suit the average family, which is why we’re focusing on this one today. Once we’ve looked at all the features you’ll be able to click over to Amazon in order to read even more things about it from both satisfied and disgruntled customers.
- It Has A Whopping Maximum BTU Of 199,000
- The Temperature Range Is Very Respectable
- It’s The Most Efficient Heater Around
- There Is Concentric And PVC Venting Options
- A High Maximum Water Flow Rate
- Size Of Your Tankless Water Heater Is Tiny
- You’ll Be Able To Change The Parts Easily
It Has A Whopping Maximum BTU Of 199,000
The BTU range of the Rinnai RUC98iN is 15,200 to 199,000, so it falls into the range we talked about before. It’s going to be powerful enough to keep the water in your home hot unless you live in a massive house and turn everything on at the same time. In other words, once you’ve bought this tankless water heater it will always be able to keep up with your needs and nobody in the shower will start screaming when the kitchen faucet is turned on.
Temperature Range Is Very Respectable
Your heater will be able to provide temperatures between 98F and 140F. This is more than you’ll ever need at home, so you’ll always be able to achieve the desired temperature you need for anything. You can actually buy a commercial remote depending on what you’re going to do with it, which will give you access to a max temperature of 185F. That is far too hot for a residential home, so unless you’re using it for commercial purposes forget about it.
It’s The Most Efficient Heater Around
It has an energy factor of 0.96, and it’s the same whether you’re using propane or natural gas. This will give you unbelievable savings from month to month. When the unit is on standby it will only need to use 2 watts compared to the normal 64 watts. This will change in winter when it gets cold, because your Rinnai RUC98iN will need to use 140 watts to protect your unit from frost depending on the temperature inside your home. The low NOx emissions also helps it achieve its Energy Star certification.
Dedicated Mode Diagram | Rinnai RUC98iN
There Is Concentric And PVC Venting Options
How many other manufacturers out there give you a choice when it comes to venting options? Rinnai is the only one to offer concentric and PVC venting options at this moment in time, which can be found in all the Ultra Series heaters. It’s always nice to have the flexibility when you’re having it installed because it can bring the price down considerably. The venting choice is actually the most important decision that will have to be made after you’ve decided which heater to buy, but luckily the person installing it will make this one.
A High Maximum Water Flow Rate
Not only will you need the water to be warm, but I’m sure you’ll also want it to flow out of the taps fast enough. If your maximum water flow rate isn’t too high you’ll end up with water crawling out of your taps depending on what you’ve turned on. The hot water flow range of the Rinnai RUC98iN is 0.26 to 9.8 gallons per minute. To put the maximum amount into context, it’s one of the highest tankless water heaters you’ll find and more than enough to provide hot water in multiple places at once.
Size Of Your Tankless Water Heater Is Tiny
This is where the average tankless water heater will shine, but the Rinnai RUC98iN goes a step further. It can be installed nearly anywhere in your home because it’s so tiny, which includes attics and crawl spaces. The unit itself measures roughly 26 x 18.5 x 10 inches, so not any bigger than a carry on suitcase. It does weigh around 80 pounds, but you’ll never notice the weight once it’s on the wall. It also comes with a separate small remote control to make life easier on you.
You’ll Be Able To Change The Parts Easily
Let’s talk about the warranty first before we get started. You’ll get a 12-year warranty on the heat exchanger, a 5-year warranty on parts, and a year on labor. All of the parts inside the Ultra Series heaters have been designed so they’re all replaceable. You’ll have the small self-diagnostic panel on the front of your Rinnai RUC98iN, and if your labor warranty has run out you’ll likely to able to change the parts it says you need if you follow the instruction manual.
Difference Between Indoor And Outdoor Water Heaters
Now we’re going to look at a couple of superb outdoor tankless water heaters, but before we do you’ll want to know the major differences between the two. Even though there are some advantages to installing your unit indoors, it’s by no means a bad idea to install one outside because of these reasons:
- They’re A Lot Easier To Install
- Dealing With Very Acidic Water
- They Have Access To A Lot More Air
- A Couple Of Minor Points
They’re A Lot Easier To Install
The reason why installation costs can be so high when you’ve bought a tankless water heater has a lot to do with their venting requirements. Even though newer models are so efficient the majority of the heat doesn’t escape back up the vent, it’s still difficult to set it up indoors. It’s easy to see why you would be able to carry out plumbing jobs easier outside when there is nothing getting in the way, whereas indoors you’ll have tight spaces, brick walls, and other various things causing problems.
Dealing With Very Acidic Water
With indoor installations you’ll need to drain the water away, which is formed due to the heat causing a lot of condensation. It’s actually very acidic and will cause your tankless unit problems if it’s allowed to seep back into the heater. The exhaust venting on the models we’re about to look at are very short, therefore you don’t end up with condensation. Considering a manufacturer could void your warranty if the damage is caused due to water venting problems it’s a nice little bonus.
They Have Access To A Lot More Air
You should know a tankless water heater will need a lot of oxygen in order to burn, but it uses more gas than a storage tank meaning the oxygen requirements are increased. If there isn’t enough it can mess with the combustion process. There is obviously access to a lot of air outside where you’ll get all the oxygen you need to keep your heater running smoothly. The air supply in your home might not be good enough, especially if you have your tankless water heater in a small closet. Finding the extra oxygen you need through holes in walls can bump up installation costs even more.
A Couple Of Minor Points
There are also a couple of other differences, although I don’t want to focus too much on them because they’re not a huge deal. If your heater is outside you’ll have even more space available, but this should only matter to people if they’re stuck in a tiny studio apartment in the middle of Hong Kong. Anyone with a normal-sized home isn’t going to find indoor models an inconvenience. The outdoor models are specially designed to withstand all the elements too, so keeping your heater outside isn’t going to affect the longevity of the unit.
Rheem Tankless Water Heater | RTG Series
We’ve looked at a marvelous indoor tankless water heater, so you might want to take a look at an outdoor one. We’re actually going to look at two in the Rheem RTG Series, but like the Ultra Series they’re almost identical so we’re going to cover the big differences between the individual models first:
- Rheem RTG-95 XLN | 9.5 gal/min. at 35-Degree Rise
- Rheem RTG-64 XLN | 6.4 gal/min. at 35-Degree Rise
Rheem RTG-95 XLN | Tankless Water Heater

Features:
- 11,000 to 199,900 BTU max
- 9.5 GPM raising water temperature by 35°
- 7.4 GPM raising water temperature by 45°
- Next Generation Burner Technology
- Low Activation Flow Rate : Less than .45 GPM
- UMC-117 remote control and 10ft of thermostate wire is included
- 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
- Exclusive! All Rheem models can be linked in up to 20 unit manifold installations by using the optional MIC-180 and MICS-180 manifold control assembly
- High-altitude capability-up to 9,840 ft. elevation above sea level (no chip required)
- Exclusive! Guardian OFW overheat film wrap
- All Rheem tankless models are third-party efficiency certified by GAMA
- Continuous hot water, energy saving and compact space saving design
- Intelligent electronic controls designed to increase energy efficiency and safety
- Self diagnostic program
- Digital display shows temperature setting and maintenance codes
- Built-in electric blower
- Supplied with a 120 volt power cord
- Environmentally friendly Low NOx burner meets SCAQMD rule 1146 requirements
- Freeze protection to -30° F
- 11,000 – 199,900 BTU max
- Temp Range 85 to 140° F
Rheem Documents:
- SPECS : Rheem RTG Series
- BROCHURE : Rheem Tankless Water Heaters
- GAS PIPING : Advice and Instructions
Rheem RTG-64 XLN | Tankless Water Heater

- 11,000 to 150,000 BTU max
- 6.4 GPM raising water temperature by 35 degrees
- 5.6 GPM raising water temperature by 45 degrees
- Next Generation Burner Technology
- Industry best 0.26 GPM Minimum Flow Rate, 0.40 GPM Minimum Activation Flow Rate
- UMC-117 remote control and 10 ft thermostat wire is included
- 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 can be linked in up to 20 unit manifold installations by using the optional MIC-180 and MICS-180 manifold control assembly
- High-altitude capability: up to 9,840 ft elevation above sea level, no chip required
- Guardian OFW overheat film wrap
- Third-party efficiency certified by GAMA
- Continuous hot water, energy saving and compact, space saving design
- Intelligent electronic controls designed to increase energy efficiency and safety
- Self-Diagnostic System
- Digital display shows temperature setting and maintenance codes
- Built-in electric blower
- Supplied with a 120 volt power cord
- Environmentally friendly Low Nox burner meets SCAQMD rule 1146 requirements
- Freeze protection to -30° F
— Main Benefits Of The Rheem RTG Series
As you can see, the only real difference is the maximum BTU and the gallons of hot water per minute you’ll be able to use throughout your home. Let’s take a closer look at the cool benefits they have in common:
- Highly Efficient Tankless Heaters
- An Exclusive Water Saving Setting
- Low Flow Fixture Compatible
- Pairs With A Recirculation Pump Kit
- Easy To Install And Diagnose
- Full Of Exciting New Technology
- Dealing With The Cold Outside
Highly Efficient Tankless Heaters
These water heaters aren’t as efficient as the Rinnai RUC98iN, but they certainly come close. The RTG Series has an energy factor of 0.82 with a copper heat exchanger. They also have electronic controls purposefully designed to increase the efficiency, and if we spread out into the impact they’ll have on the environment as a whole they have very low NOx emissions too.
An Exclusive Water Saving Setting
These heaters are capable of reducing the flow of water as it’s making its way around the system to reach the final temperature you’ve set it to. Over the course of a year you can save over a thousand gallons of water, which is a considerable amount when you see what that volume of water looks like in a pool. It’s an extra way to save money, plus extremely helpful in all areas where water is at risk of running dry.
Low Flow Fixture Compatible
If you’re in a situation where you need water it’s possible you might not get it with a tank, but the RTG Series has made this possible no matter how low the demand. In fact, Rheem claim they had the first minimum flow rate of only 0.26 GPM. As an added bonus the minimum activation flow rate sits at an impressively low 0.40 GPM. Never again will you be starved of water at any point in the day.
Pairs With A Recirculation Pump Kit
On the Ultra Series the big difference between the RUC and RUR models is the recirculation technology built into the heater. The RUC and Rheem models don’t have the same technology, but you can still get the same benefits with the RTG Series because it pairs with a recirculation pump. It means the hot water will reach your taps almost instantly once you’ve turned them on.
Easy To Install And Diagnose
Each unit is capable of attaching to 3″/5″ concentric venting without the need to use an adapter, plus every model also has 1/2″ gas line compatibility. It won’t mean much to you looking at those figures, but it means the Rheem tankless water heaters are easy to install. The self-diagnostic system will also help you diagnose any problems, and you’ll be told automatically through the use of flashing lights when it needs serviced.
Full Of Exciting New Technology
The RTG Series has a few pieces of new technology built into it, but there are a couple in particular you’ll be interested in. Do you know how you sometimes get weird fluctuations in the temperature of your water when it’s always being switched off and on? Hot-start programming was introduced to stop it from happening. There is also an exclusive film wrapped around the units to prevent overheating.
Dealing With The Cold Outside
We’ve just talked about overheating, but what happens when an outdoor tankless water heater gets too cold? The Rheem RTG-95XLM and RTG-64XLM will be able to withstand temperatures 30 degrees below zero. Even at altitudes high above sea level at 8,400 feet in the air where it’s always cold. You will also get a thermostat with 10ft of wire and a digital remote control so you don’t need to trek outside all the time.
Rinnai RUC98iN Has More Pros Than Cons
In general, tankless water heaters have much more pros than cons. You’ll have the ones you see straight away like the newfound space inside your home, and you’ll also have the ones you won’t see for years like all the money you’ll eventually save. When it comes to the Rinnai RUC98iN itself, it’s hard to find a better indoor tankless water heater than anything in the Ultra Series.
If you’re considering upgrading your water heater it should be the first one you investigate due to its popularity. If you pay Amazon a quick visit you’ll read reviews from dozens of people who have it installed right now. Reading the comments it’s easy to see why it’s loved more than a lot of the other tankless water heaters currently available.