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Rheem RTEX-18 Electric Water Heater Review

Rheem RTEX18 Electric Water Heater

There are many Rheem RTEX 18 specs and reviews available online, but this one will go a step further.

We will provide you with all the information you need to know about how the heater works, why do you need it, and what sets it apart from the other competitors. Here is a quick recap on what we think of this tankless water heater.

Our Rating
Rheem RTEX 18 specs and reviews
  • Saves electricity
  • Compact
  • Very Durable
  • Self Modulating

Rheem Rtex 18 Specs and Reviews

Dimension & Design

This model weighs at only 8.5 pounds, with the dimensions of 4 x 15 x 19 inches.

It is a relatively small water heater. The RTEX 18 has an ON/OFF dial control with adjustable digital temperature display.

The control panel is stylish with 1°F ranging from 80°F to 140°F.

Water Flow and Voltage

This model delivers up to 4.4 gallons of hot water per minute (GPM). The water is at an accurate and consistent temperature. The voltage of this model is 240 volts.


  • Standard Hand Sink – 0.5 GPM
  • Dishwasher - 1 to 2 GPM
  • Washing Machine - 1 to 1.5 GPM
  • Water-saver Shower Head - 1.5 GPM
  • Standard Shower Head - 2.0 GPM
  • Bath Tub - 4 GPM
  • Kitchen Sink - 1 to 2 GPM


It comes with a 1-year parts limited warranty for all residential installations, a 5-year warranty on all its heating chamber.

What Makes This Heater Stands Out?

1. No heat loss

Bulk heaters are the first thing that comes to mind when we think of water heaters. These are large, clunky tanks of water with heating units inside.

They store a certain amount of water and heat it up gradually over a relatively long period of time. In order to minimize heat loss, manufacturers insulate them heavily.

However, a certain amount of heat always escapes. That is because there is a time gap between when you heat the water up, and when you use it.

That means you are effectively wasting electricity by using bulk heaters. The Rheem RTEX 18  eliminates this problem entirely.

2. Savings on electricity

The Rheem RTEX 18 heater has an energy efficiency of 99.8% which helps to save you money on electricity bills.

Depending on the type of heater in question, these savings can vary, but they are always an improvement on bulk heaters.

Furthermore, all tankless water heaters produce fewer greenhouse gases than bulk heaters. That makes them good for the environment as well.

Heat retention is not the only thing that contributes to the efficiency of the Rheem RTEX 18. Another important factor lies in the way it functions. Namely, it only uses electricity when hot water is needed.

That is why these are also called ‘on demand’ water heaters, because they only work when you tell them to.

Check out this article if you are looking for gas type water heaters instead.

3. Durability

Bulk heaters have to retain water in a tank in order to heat it up. That leads to problems with corrosion and plaque buildup.

Experience has shown that the Rheem RTEX 18 can last up to 10 years longer than bulk heaters.

This longevity is due to the fact that it has a robust copper immersion heating elements with brass top therefore less prone to corrosion. And you can clean or replace the pipes easily.

4. Save space

The Rheem RTEX 18 is very popular in Europe. That is because apartments in Europe often have limited space, and rents are high.

People need to be smart about how to use that space. Having a large bulk water heater is not a smart solution.

Thus, people in Europe have opted for tankless water heaters, generally, with the Rheem RTEX 18 being one of the most popular models.

That is because they can put it almost anywhere. They put the Rheem RTEX 18 inside cabinets, in closets, and generally out of the way.

However, if you are looking for a more compact-sized electric water heater for a smaller living space, please read our review on Rheem RTEX-13, another great option for a cheaper price.

5. Safety concerns

As previously mentioned, the Rheem RTEX 18 is safer than bulk heaters. Bulk heaters tend to corrode over time, which can lead to structural damage.

Once a bulk heater starts leaking, or even worse, if it bursts, there is no way to stop it.

That is why bulk heaters can lead to flooding, if not handled properly. If the Rheem RTEX 18 malfunctions, all you need to do to stop leaks is shut off the nearest valve.

6. Limitless hot water

For people looking to make the switch, this is the most important factor. With the Rheem RTEX 18, you will never run out of hot water.

Since it heats water up ‘on demand’, as long as you have running water and electricity, you will have hot water. That eliminates the chance of cold water surprises in the shower forever!

Other Types of Applications:-

How Does the Rheem RTEX 18 Tankless Water Heater Work?

People new to the concept of tankless water heaters often wonder about the way in which they work. It’s actually pretty simple.

Instead of storing the water and heating it up gradually, the Rheem RTEX 18 does so while the water is flowing past it. For that to happen, you need to install it on the pipes themselves.

To heat the water up, the Rheem RTEX 18 uses a heat exchange unit. These are designed to achieve high temperatures, which they transfer to the water.

They work using electric induction. This is when an electric current is passed through resistant materials, producing heat.

Editor's note: The Rheem RTEX 18 is a prime example of all the benefits you could hope to get out of a tankless water heater. It is a well-designed and efficient water heater, that gets the job done without much fuss.

Pros and Cons


  • Saves space: This unit is designed to be as compact as possible, while producing reliable results. That means it can fit in where other water heaters would have trouble.
  • Digital thermometer : The digital thermometer on this unit is a very useful feature. It can help you set the appropriate temperature for your water, and save energy at the same time. 
  • Self-modulating : The feature is crucial to provide a steady amount of water at a certain temperature. It allows the heater to adapt to changes in the temperature of the input water, so as to keep the output water at the same temperature.


  • One tap at a time : You can consider this either a pro or a con, depending on how you look at it. The fact is that this heater can only handle one tap at a time. People who expect one of these to power an entire house will be disappointed

People have used this model to get hot water in areas where there isn’t much room for installations. However, you shouldn't use this to power an entire house. For that, you need a larger model. You can also check out other great brands here.

Final Verdict

Rheem RTEX 18 Electric Water Heater

We hope you find our comprehensive Rheem RTEX 18 specs and reviews useful.  Our verdict is, the Rheem RTEX 18 is a fantastic investment if you are looking for a basic model of tankless electric water heater. We rate this model 4.5 stars out of 5.

Our Rating
  • Saves electricity
  • Compact
  • Very Durable
  • Self Modulating
Rheem RTEX 18 Electric Water Heater

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    Verner Ellen

    Hi, my name is Verner Ellen. I am a homebody whose interest is in getting the best home tools and equipments to help with the the everyday house chores. I also love fitness, cooking and grilling. Maintaining a clean and comfortable home is my lifelong passion.