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Rinnai RU199iN Tankless Hot Water Heater Review

Are you tired of paying hefty electric bills simply due to using an electric water heater? If you are, then you’re not alone with this problem.

Thousands of homeowners have to worry about rising power bills when using electric water heaters. However, there’s a simple, cost-effective solution to this issue in the form of tankless gas water heaters.

Natural gas tankless water heaters provide you with continuous hot water at a fraction of any electric water heaters’ cost. And though they are initially a bit expensive, you can quickly recover the cost in the long run by saving on electricity bills.

However, it makes sense to ensure that you end up with a suitable one for your needs. To help you do that, we’re here today with a comprehensive guide on the best tankless gas water heater that money can buy.

Let’s get the show on the road then.

Our Top Pick

Rinnai V75IN Indoor Tankless Hot Water Heater

When it comes to gas tankless water heaters, Rinnai is a name that’s well known worldwide. The V75IN indoor tankless hot water heater is a compact and portable unit that’s made with the modern homeowner in mind. With a 7.5 GPM hot water flow rate, this is one model that you won’t want to miss out on.

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How Tankless Gas Water Heaters Work

But how can a water heater be…well…tankless?

The very concept of a tankless water heater can seem counterintuitive to many. After all, shouldn’t you need a water tank for the heater to work? Thankfully, these water heaters use a direct-heating technology that doesn’t need the use of a tank.

For this reason, tankless water heaters are also known as on-demand water heaters, as they heat the water only when you need it. This way, they avoid the energy loss that’s usually associated with tank-based water heaters.

Curious to know more? Then read on to know all about how tankless gas water heaters work!

Going Back To The Basics

If you’re going to understand how a tankless gas water heater works, it’s essential to know how tank-based ones operate. When using a traditional water heater in your home, you’ll have to deal with a sizable tank that will take up a significant amount of space.

In these old-fashioned water heaters, the tank holds the water and keeps on heating it continuously to maintain a steady temperature. That way, you can get the hot water any time by just turning on the faucet.

However, there’s a catch: standby loss of heat. This is the energy that’s being lost to keep the water hot even when you’re not using the heater. Naturally, tank-based water heaters require more energy to keep running and result in higher utility bills.

This is precisely the problem that tankless water heaters look to avoid. These water heaters eliminate standby loss of heat by heating the water as and when you need it. Hence, they are also known as “on-demand” water heaters.

The Working Mechanism Of A Tankless Gas Water Heater

Tankless water heaters can be electrical or gas-powered; in general, electric water heaters heat the water at the point-of-use. On the other hand, gas tankless water heaters are usually whole house water heaters that work for the entire water supply. However, you do get portable tankless water heaters that run on gas.

A gas tankless water heater works by using a heat exchanger that raises the water’s temperature as and when you need it. A heat exchanger is essentially a system that transfers heat from one source to another.

The heat exchanger transfers heat generated by a gas-powered burner to the water in your pipes. In tankless water heaters, this exchanger activates by sensing the flow of water in the pipes.

So, when you turn on the faucet and the water begins to flow through the heat exchanger, it gets activated and starts transferring heat from the gas-powered source. This way, it heats the water to the preset temperature levels that you’ve chosen.

Tankless Gas Water Heater Operation In 8 Steps

  1. First, you turn on the hot water tap or shower
  2. The moment that’s done, a flow sensor senses the water coming into the heater and signals the control panel to start producing hot water
  3. The control panel then turns on the fan and draws in air from the outside
  4. Next, the gas valve opens to initiate gas flow, and the burner ignites
  5. Now, the heat exchanger transfers the heat from the burner to the water in the tubing
  6. The mixing valve tempers the superheated water
  7. Before the water is released, the temperature sensor tests if the water temperature matches the desired levels
  8. Finally, the vents carry away the exhaust fumes

This entire process happens in less time than it took for you to read through the above steps. So, you virtually get hot water the moment you turn on the faucet, provided the flow rate and groundwater pressure are adequate.

The significant advantage of using a gas tankless water heater is that you don’t have to wait for the tank to fill up with sufficient hot water. You can directly turn on the heater and start using hot water the moment you need it.

That said, in a tankless water heater, the water flow rate is often a bit low, though gas-powered water heaters usually have higher flow rates than the electric variants. In case you need a greater flow rate, you can connect multiple tankless water heaters in parallel.

Types Of Tankless Gas Water Heaters

Now that you know how a gas tankless water heater works, it’s time to look at the different types of tankless gas water heaters available in the market. In the following sections, we’re going to segregate them according to the technology and kind of use you can put them to.

A. Types Of Tankless Gas Water Heaters Based On Technology

1. Condensing

Condensing gas tankless water heaters are an advanced generation of tankless water heaters. These models use a secondary heat exchanger along with the primary exchanger unit that uses exhaust-fume heat to raise the water temperature more efficiently.

Condensing tankless water heaters usually have efficiencies in the range of 92% to 94%. Another advantage of this type of heater is that they have a cooler exhaust and can use low-cost PVC piping for venting the heat. However, they do have a higher initial cost and are not very suitable for low water uses.

2. Non-Condensing

Non-condensing tankless water heaters belong to the first generation of gas tankless water heaters. These units use a single heat exchanger for on-demand water heating and have a lower efficiency of about 82% to 85%.

This type of water heater technology was initially more popular in Europe and Japan but eventually caught on in the US. The advantage of using this type of unit is that the technology has developed over decades, and hence you’re less likely to face significant issues.

However, the one drawback of this type of tankless gas water heater is that they have a pretty hot exhaust. As a result, you’ll have to invest in expensive stainless steel vents. Plus, they are known to have much lower efficiency than usual when you’re drawing water in short intervals.

3. Hybrid

Hybrid gas tankless water heaters were first created and used in the US and work to combine the best of both the above types. However, it would be wrong to call them entirely “tankless” as these units have a small (usually in the range of 1-2 gallons) water tank that holds water for shorter draws.

The advantage of using this auxiliary holding tank is that it improves efficiency if you need short draws of hot water at regular intervals. Unlike traditional condensing heaters, which show degradation on faster draws, these units have a steady efficiency of 92% to 96%.

Another advantage of using this type of unit is that it can use PVC piping as vents. This helps to lower the overall cost associated with installing the unit. Hybrid units are also known to have less pressure fluctuation and marginally less lag time. However, since this is still a new technology, you can expect manufacturing issues to crop up at times.

B. Types Of Tankless Gas Water Heaters Based On Use

1. Whole House Water Heaters

This is the most common type of gas tankless water heater that you can find. If you’re a homeowner who wants a water heater that can supply hot water to all the faucets, then go for this type with your eyes closed.

When selecting a whole house water heater, keep the flow rate in mind. This is the number of gallons that the heater can supply per minute, also known as GPM. The higher the GPM rating of your unit, the greater the number of simultaneous faucets and showers you can run.

Also make sure that you’ve considered your location’s ambient temperature when selecting a model. If you live in colder climes, then the heater should have sufficient capacity to heat the cold groundwater to your preset levels.

2. Commercial Water Heaters

Commercial water heaters usually have higher flow rates and BTUs since they are natural gas or propane powered. These units are suitable for business establishments such as hotels that have higher hot water requirements. Often, they have recirculation systems that help reduce that water wastage.

3. Portable Water Heaters

For those looking for a low-cost water heater to use on-the-go, portable water heaters are the best option. These units are lightweight and can work in RVs and mobile homes. You can even take one on camping trips so that you don’t have to skip that hot bath.

4. Outdoor Gas Tankless Water Heaters

As the name suggests, these units are for installation outside a house. Outdoor tankless water heaters work by utilizing the atmospheric airflow for venting purposes. This helps reduce costs associated with putting in separate vents.

Since these water heaters don’t need extra venting, their installation process is easier, faster, and less costly. In many cases, they can be designed with self-warming components, allowing them to operate even in lower temperatures.

Keep in mind that if you live in an area with long periods of sub-zero temperature, this type of heater might not be the best option.

Our Top Product Picks


Rinnai V75IN Indoor Tankless Hot Water Heater

When it comes to gas tankless water heaters, Rinnai is a name that’s well known worldwide. The V75IN indoor tankless hot water heater is a compact and portable unit that’s made with the modern homeowner in mind. With a 7.5 GPM hot water flow rate, this is one model that you won’t want to miss out on.

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  • Ergonomic and lightweight build
  • Easy to install and maintain
  • Works in any domestic or even commercial setting
  • Powerful operation
  • Extra focus on safety


  • Rather expensive product

What Could’ve Been Better?

The one gripe that many customers have about the V75IN is that it’s a bit too pricey. The unit’s price, together with the cost of getting it installed, can become prohibitive if you’re operating on a tight budget.

However, as we’ve already mentioned before, tankless water heaters cost higher initially. But since they pay for themselves many times over in terms of utility bills, we don’t think anyone should pass over this unit for saving a few extra bucks in the short term.

Another thing that you should be careful about is the packaging. Many customers have complained that the product comes poorly packed, which might lead to damage in transit. So, make sure you’re receiving a well-packed unit when taking the delivery.

Why Buy This Product?

1. Highly Ergonomic Design

One look at this device, and you’ll be able to tell that the company has put enough research behind it. It has a compact size of just 14 x 9 x 27 inches and is ideal for smaller and mid-sized homes that are low on space.

The compact dimensions are a direct result of a closed combustion system and a concentric venting system. Due to the compact size, it can also be used in any commercial space. Unlike water heaters with tanks, it is relatively inconspicuous and can be tucked into any corner. Plus, the cool white look also adds to its aesthetic appeal.

2. Power-packed Performance

If you’re thinking that the small size of the device means a compromise on power, then you’re sorely mistaken! Even when used regularly, this tankless heater is sure to deliver a powerful performance. With an output rating of 180,000 BTUs and a flow rate of 7.5 GPM, this is a powerful system in a neat little package.

The high heating capacity ensures that it can take care of all your home’s hot water needs, with more to spare. The device’s energy factor of 0.82 provides optimized performance, and the temperature range of 98 to 140 degrees Fahrenheit allows you to choose any temperature as per your needs.

3. Low-maintenance Product

The next aspect that we’d like to highlight is the low maintenance and easy installation capacity of this unit. Rinnai uses concentric direct venting for this model, which allows it to be easily installed even in closed spaces.

Simultaneously, we like how it comes with a detailed instructions manual that further helps in the installation. Add to that the ten years warranty on the heat exchanger and five years on the parts, and you’ve got a device that’s virtually maintenance-free.

4. Advanced Safety Features

In terms of safety, the V75IN includes a scale control system that prevents damage due to scale accumulation. It also has a temperature lock that controls the level of hot water that’s produced.

Further, the device comes with a frost protector that ensures that the water in the pipes doesn’t damage it. It also includes an electronic ignition mechanism that saves energy and improves the device’s efficiency.

5. Environment Friendly And Versatile

This tankless heater runs on propane as well as natural gas and helps to minimize pollution. The anti-pollution property is further enhanced by the integrated eco-gas burner provided by Rinnai. It ensures lower levels of NOx, thus further protecting the environment.

Finally, its versatility is unmatched, as it can be used in manufactured as well as mobile homes with ease. Add to that the fact that it can operate at altitudes of over 10,000 feet, and you’ve got a tankless water heater that you can use under any conditions.


Rheem RTGH-95DVLN 9.5 GPM Tankless Hot Water Heater

The next gas tankless water heater we have for you is the RTGH-95DVLN from Rheem, a 9.5 GPM powerhouse. With a 94% energy efficiency rating and stainless steel heat exchanger, this is a product that delivers a great combination of safety and efficiency. It also provides intelligent electronic controls that work to make the operation effortless.

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  • Massive 9.5 GPM flow rate
  • High energy efficiency rating
  • Fully remote-controlled operation
  • Adequately protected against freezing temperatures


  • Steep price tag
  • Possible lack of customer support

What Could’ve Been Better?

As you might have guessed already, the unit’s price is rather steep due to so many advanced features. So, if you live in a small house and don’t have significant hot water needs, it’s best to consider less expensive options.

The next point of contention that we have is that even though it has a warranty of 12 years, many customers have complained about the lack of customer support. However, we’re yet to face any such problem with the brand.

Why Buy This Product?

1. Impressive Energy Efficiency Rating

In today’s world of global warming and rising fuel bills, we all strive to lower our carbon footprints. This tankless water heater can help with that as it has a high energy star rating of 0.94. This means it’s 94% energy efficient and helps to reduce your gas consumption significantly.

At the same time, the product’s body is made of stainless steel, which ensures that the inner mechanism is not affected by external weather conditions. It also uses condensing technology to get the most heat from exhaust gases; this only adds to its energy-efficient nature.

2. Smart Control System

Often, we get customers complaining that operating and changing their natural gas tankless water heater’s settings becomes a hassle. With this model, you’ll have no such trouble as it comes with a remote that provides you greater control over the device.

Rheem has also taken the pains to install a bright LED display and smart control system that helps users save energy and alter the unit’s temperature settings with ease. Overall, if you’re getting this device, then you won’t have to worry about getting up to change heater settings.

3. Massive Capacity

Next, we have to discuss the model’s flow rate capacity, which is massive by any standards. It has a considerable flow rate of 9.5 GPM, which is enough to supply hot water to three showers running in full flow. You can even connect multiple units in tandem to increase the overall water flow capacity.

4. Adequate Safety Features

Similar to the previous tankless water heater from Rinnai, this model from Rheem also takes safety seriously. It has been certified by the AHRI and can defend itself against freezing temperatures up to thirty degrees Fahrenheit below zero.

It also comes with a self-diagnostic utility that constantly monitors the heater’s function. In case there’s a problem with the gas or water supply lines, the system will automatically warn you of it. This makes it an extremely safe unit for use in households with kids and pets.

5. Advanced Feature Set

If even the above features don’t have you that impressed, then sit tight, for there’s more coming! The device has a hot-start programming option that lets you control the level of water temperature fluctuation.

It even comes with an Overheat Film Wrap that protects against heat exchanger breaches. And the icing on the cake is that this is a low-NOx unit, so pollution will be the least of your concerns.


Rinnai RU199iN Tankless Hot Water Heater

We’re back again with another Rinnai product, this time the RU199iN natural gas tankless water heater. Like all Rinnai products, this one is a durable unit that packs a massive 199,000 BTU of heat output. At the same time, it’s super-quiet and packs several features that justify its high cost.

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  • Extremely powerful with a high flow rate
  • Super-quiet operation
  • Usage pattern-based pre-programming
  • WiFi monitoring system


  • Doesn’t come with the required piping
  • The installation process is highly complex

What Could’ve Been Better?

Apart from the price factor, the only fly in our ointment is that it doesn’t come with any piping included. This means you’ll have to get the piping separately, which will only add to the unit’s already steep price.

Simultaneously, we have to admit that installation for this water heater is not as easy as the previous items on the list. It has a rather complicated set-up process, and you’ll have to invest in professional help to get the unit installed correctly. Naturally, this means more spending, which many might not be willing to foot.

Why Buy This Product?

1. High-power Output

The RU199iN utilizes a highly efficient condensing unit that reuses hot exhaust gases for heating water. This enables it to heat water using lesser fuel, thus lowering your utility bills and carbon footprint in a single sweep.

This gas water heater’s minimum consumption capacity is 15,000 BTU, while the maximum rating hovers around 199,000 BTU. These ratings alone are enough to tell you that this is a unit that doesn’t pull back any punches when it comes to heat output.

2. Superior Flow Rate

Next, let’s take a look at the flow rate, which at 11 GPM is the highest among all the options we’re reviewing here. Naturally, you’d have to understand that this flow rate is the maximum rating and can vary according to the groundwater force.

The high flow rate ensures that you never have to go without hot water for any of your household needs. Whether you’re looking to run multiple showers or work with multiple faucets on, this one can handle it with ease.

3. Advanced Circ-Logic Mechanism

No review of this model can be complete without mentioning its Circ-Logic mechanism. This is an advanced heating technology that speeds up the time you need to get the required hot water.

The technology allows you to set up pre-programmed recirculation patterns which coincide with your water use habits. This way, you won’t have to wait a moment to get hot water after turning on the faucet.

4. Compact And Reliable

Despite packing so much power and technology, the design of this tankless heater focuses on saving space. The entire unit weighs just 64 pounds and has compact dimensions of 18.5 x 11.45 x 31.3 inches. Install it easily in any corner of your house and forget about it.

5. Additional Features

We’ve already mentioned that this tankless water heater is extremely quiet, so you don’t have to worry about any naps getting disturbed. Along with that, it also includes a WiFi-based monitoring system that helps in the pre-circulation programming. What’s more, you can easily monitor the efficiency of the unit from your smartphone.


Eccotemp i12-LP Tankless Water Heater

Up next is a whole house propane tankless water heater that works to supply hot water to every faucet of your home. The i12-LP from Eccotemp is an entirely tankless model and is propane-powered. So, you won’t have to worry about dealing with high utility bills. At the same time, it also packs advanced features such as an LED control panel.

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  • Energy-efficient design
  • LED display and controls
  • Includes most required accessories
  • Advanced design with child-lock


  • Low output per minute
  • Complex installation process

What Could’ve Been Better?

There are two aspects that we’d like to improve in this model. The first one is the output, which we think should increase from the 4 GPM. The second is that the installation process is a bit tricky, so you might need to spend on professional help.

Why Buy This Product?

1. Compact And Sleek Design

The very first thing that catches anyone’s eye about this model is its sleek black look. The front panel has a tempered glass covering, which adds to the aesthetics and lends extra robustness to the product.

Since it’s primarily made for small to medium-sized homes, this unit doesn’t require much space. In case you’re running low on space but still have to install a water heater, this is the ideal choice.

2. Optimal Temperature Range And Flow Rate

Although the flow rate of the i12-LP caps at 4 GPM, which is a lot less than the above water heaters, still it’s enough for modest domestic use. Plus, it has a heating capacity of 80,000 BTU per hour, which is sufficient for most users.

If you’re operating the device at 3 GPM, you can expect a temperature rise of 35 to 40 degrees Fahrenheit. For a more significant temperature rise of about 77 degrees Fahrenheit, you can operate the heater at 1.5 GPM.

3. Electronic Ignition System

One of the significant aspects of this model is that it doesn’t need a pilot light for operation despite being a propane tankless water heater. Instead, it uses an electronic ignition system to power the gas tankless water heater safely. Add to that a safety child lock, and you’ve got virtually nothing to worry about.

4. Durable And Efficient Construction

Overall, the unit’s operation is highly fuel-efficient, and you don’t have to worry about spending too much on propane to get this one running. Plus, it also comes with a stainless steel vent kit that provides long-term durability.

What To Consider When Buying A Tankless Gas Water Heater

We’ve already taken you through our picks of the four best gas tankless water heaters, along with a brief overview of how such water heaters work. You also know about the different types of tankless water heaters that you can buy.

But the real question remains unanswered, how do you select the best tankless gas water heater for your needs? Honestly speaking, the task is easier said than done, for there are quite a few aspects that you need to consider before selecting one.

Thankfully, you have us to help you out! That’s why we’ve prepared a list of the factors that you need to consider when buying a tankless gas water heater. Keeping these in mind will help you make a better choice.

1. The Size

For any water heater to satisfy your requirements, it needs to be of the correct size. A tankless water heater that’s too small is likely to have a lower flow rate, and one that’s too large will require more fuel to run, thus increasing the running cost of your device.

So, before selecting a tankless water heater, make sure to take stock of the number of faucets and showers in your house. It’s always wise to go for a model with an adequate flow rate to support simultaneous use.

2. The Fitting Location

Along with the size, you’ll have to consider the location where you’re going to fit the water heater. The size of your heater will depend to a large extent on the fitting site.

In case you’re fitting a smaller water heater, you won’t need much space and can directly install it in any suitable location inside the house. For a larger, whole-house water heater, you’ll have to install it somewhere spacious like the garage.

3. Energy Efficiency

It’s no secret that tankless water heaters are more costly than traditional ones. So naturally, you’d want them to be more energy efficient to lower your fuel bills. Thankfully, like most devices these days, gas tankless water heaters also come with energy ratings.

The Energy Rating is a measurement of how efficiently the device utilizes a single gas unit to produce heat. The higher the energy efficiency, the more heat your device can produce per unit of fuel. It’s best to go for one with an Energy Rating that’s above 90.

4. Flow Rates

Along with the heater’s size, the flow rate is one of the essential factors you need to consider before buying a tankless water heater. Flow rate is a measure of the amount of water that the device can heat in a specific amount of time.

Flow rates are usually measured in terms of Gallons-Per-Minute, abbreviated as GPM. The higher the GPM, the greater the flow rate. This rating is typically available on the device package or the website listing (if you’re buying online).

However, the flow rates mentioned on the device packaging can vary based on the number of fixtures that you’re operating at once. In case you’re going to use multiple components that need hot water, you need to opt for a heater with a higher GPM. If you’re not sure about the ideal GPM rating you need, speak to a professional water heater expert.

5. Temperature Rise

If you’ve been using water heaters (whatever the type) for a while now, then you know that there’s always a difference between the groundwater temperature and the water that comes out from the faucet. This differential is known as Temperature Rise, and the ability to handle this can vary from device to device.

Now, how do you measure this metric? To get a ballpark figure, simply subtract the incoming water temperature (before it hits the water heater) from the preset temperature level of your device.

As you can probably understand, this differential will depend mainly on the region where you live and the ambient temperature while using the water heater. For typical household uses, you’d want the water coming out from the heater to be at least above a hundred degrees Fahrenheit.

Of course, that depends on the exact needs of your household and even personal preferences. Just bear in mind that the higher the incoming water temperature and the lower the preset temperature, the lesser your energy consumption; naturally, the reverse also holds true.

6. Heater Type

The next aspect to keep in mind is the type of gas tankless water heater that you’d like installed on your property. If you need a simple, low-capacity unit for the kitchen or one bathroom, you can opt for a point-of-use model. However, for better coverage, it’s recommended that you go for a whole-house model.

Also important is whether you’d like to go for a condensing, non-condensing, or hybrid model. To get a better idea of the different types of tankless water heaters, please visit the above section.

7. Budget

Finally, love it or hate it, you have to consider the budget. We’ve already mentioned that tankless water heaters cost more upfront than tank-based water heaters. Since these water heaters are more energy-efficient and have a greater life span, they are more affordable in the long run.

Tankless gas water heaters usually have a lifespan of 20 years or more. They also come fitted with easily replaceable components that are pocket-friendly. So, be sure to factor in these aspects when you’re preparing the budget for your tankless gas water heater.

Final Words

Whatever the season, nothing beats a hot shower at the end of the day to relax your body and soul. And a gas tankless water heater can help you get just that with minimal space requirements.

We hope you’ve been able to find the best model for your needs after going through this guide. In case you want to go through it once again, please do so. And we recommend keeping the points of the buyer’s guide in mind when making a selection.

Before we leave, a quick overview of our favorites: the Rinnai V75IN is the best option overall, though it’s a bit too expensive. If you’re looking for higher flow rates, then consider the Rheem RTGH-95DVLN or Rinnai RU199iN. And if looks are your primary concern, then nothing beats the Eccotemp i12-LP.

With that, we’ll now take your leave. Stay safe!

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