Layer 1

Rheem RTGH-95DVLN 9.5 GPM Tankless Hot Water Heater Review

Our Top Pick

Check Price at Amazon

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


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.

Check Price at Amazon


  • 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.

Layer 1