Rheem RTEX-18 Electric Tankless Water Heater

Rheem RTEX-18 Electric Tankless Water Heater Review

  • A reliable and energy-efficient hot water solution is essential in today’s fast-paced world.
  • The electric Rheem water heater boasts a range of specifications that make it an impressive addition to any household. 
  • The array of features in the Rheem electric tankless water heater is designed to enhance user experience and energy efficiency.
  • The Rheem water heater range encompasses a versatile selection of tankless water heaters.

Ideal for households, these Rheem tankless water heaters are tailored to deliver efficient hot water on demand.


A reliable and energy-efficient hot water solution is essential in today’s fast-paced world. This comprehensive Rheem RTEX-18 electric tankless water heater review delves deep into its specifications, features, and maintenance tips. We also examine the warranty details and performance to provide an informed perspective. Rheem water heaters stand out as a game-changer in this domain. We shall explore the broader range of Rheem tankless water heaters as well.

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The electric Rheem water heater boasts a range of specifications that make it an impressive addition to any household. It has a heat output of 18kW, a maximum operating pressure of 150, and a GPM of up to 4.4. This ensures an uninterrupted hot water supply, catering to various needs. Its compact design and cutting-edge technology make it a space-saving and efficient choice for modern homes.


The array of features in the Rheem electric tankless water heater is designed to enhance user experience and energy efficiency. From the external digital thermostatic control with LED display, and advanced self-modulation. It also features two copper-immersion heating elements. Each of these aspects contributes to its standout performance. Moreover, its able to serve two showers and two sinks simultaneously. This ensures that you have hot water on demand while optimizing energy consumption.

ItemRTEX-11 RTEX-18 RTEX-24 
GPM (Max)Up to 2.68Up to 4.4Up to 5.9
Power Source240V electric240V electric240V electric
Kilowatt (Max)11kW18kW24kW
Fixtures served (Max)1 shower, two sinkstwo showerstwo showers, two sinks

Types of Rheem RTEX-18 Electric Tankless Water Heaters:

The Rheem water heater range encompasses a versatile selection of tankless water heaters. They are designed to accommodate a wide spectrum of user requirements. Within this lineup, you’ll find:

1. Residential Models: 

Ideal for households, this Rheem RTEX -18 electric tankless water heater is tailored to deliver efficient hot water on demand. They come in various sizes. This allows you to select the perfect capacity based on the number of occupants and anticipated water usage. These models are a popular choice for homeowners seeking energy-efficient solutions without compromising on comfort.

2. Commercial Models: 

Rheem extends its innovation to commercial settings with tankless water heaters engineered to meet higher demand. These models are robustly constructed to deliver consistent hot water for businesses, hotels, restaurants, and other commercial establishments. Their larger capacity and durable design ensure uninterrupted performance in high-traffic environments.

According to Statista, Rheem accounted for a quarter of the US market share in 2020.

3. Outdoor Models: 

Rheem offers outdoor tankless water heaters for those who prefer to save indoor space. Rheem offers outdoor tankless water heaters for those requiring installations in regions with mild climates. These units are built to withstand the elements and provide hot water without taking up valuable indoor square footage.

4. Condensing Models: 

Condensing tankless water heaters from Rheem incorporate advanced technology to extract heat from exhaust gases, maximizing energy efficiency. These models are an excellent choice for environmentally-conscious users aiming to reduce energy consumption and carbon footprint.

5. High-Efficiency Models: 

Rheem’s high-efficiency tankless water heaters combine cutting-edge design with eco-friendly operation. These models are engineered to minimize energy wastage. They allow users to enjoy substantial energy savings while enjoying a steady supply of hot water.

Each type of Rheem tankless water heater carries its distinctive advantages. This allows users to choose what aligns seamlessly with their specific hot water needs and energy-saving aspirations. Is the heater for a cozy home, a bustling business, or an outdoor installation? Rest assured Rheem’s diverse range ensures that the perfect tankless water heater is within reach.

According to Statista, Rheem accounted for a quarter of the market share in the US in 2020.  

Rheem RTEX-18 Electric Tankless Water Heater Maintenance:

Regular maintenance is crucial to ensure the longevity and optimal performance of your Rheem tankless water heater. Implement simple practices such as regular flushing, inspection for leaks, and temperature checks. This can go a long way in preserving its efficiency over the years. Adopting these practices allows you to enjoy consistent hot water without worrying about unexpected breakdowns.

Rheem Water Heaters Warranty:

Rheem takes pride in the durability of its products, and the Rheem RTEX-18 electric tankless water heater is no exception. The six-year warranty gives users peace of mind, knowing their investment is safeguarded. Understanding the warranty terms empowers users to make the most of their Rheem water heater. You will also have recourse in case of any issues.

Rheem Water Heater Customer Service:

A reliable customer service network adds an extra layer of trust to any product. Rheem’s prompt customer service ensures that users receive timely assistance for Rheem water heater troubleshooting, installation, and any other queries. This robust support system enhances the overall user experience.

Pros and Cons:

As with any product, the Rheem electric water heater has its own set of pros and cons. On the positive side, it is easy to install; it is small and therefore frees up space. The fact that it costs less than a tank heater is a huge plus, making it a competitive choice in the market. However, remember that maintenance must be done once a year to flush hard water. This process will require you to purchase more equipment. Put these aspects into consideration when evaluating its suitability for your specific requirements.

Top 3 Residential and Commercial Models of Rheem:

Besides the RTEX-18, Rheem offers other notable tankless water heater models. These include:

1. Rheem Prestige Efficiency Natural Gas Tankless Water Heater:

Introducing the Rheem Prestige Efficiency Natural Gas Tankless Water Heater. Here is your gateway to a world where hot water flows without delay. This heater eliminates both the inconvenience of waiting and the wastage of resources. It is designed to deliver immediate comfort and long-term benefits. This tankless water heater boasts an impressive combination of low operating costs and remarkable energy efficiency. It ensures that your utility bills remain manageable while you enjoy a consistent supply of hot water. It comes with a compact design with a commitment to both functionality and space-consciousness, it comes with a compact design.

This is perfect for those seeking a tank replacement solution that optimizes room utilization. Safety is paramount, and this heater takes it seriously with its water and gas leak detection feature. This feature automatically shuts down the unit and provides a clear error code in case of any anomaly. It’s important to note that this innovative solution is designed exclusively for indoor use. It caters to your hot water needs without compromising on safety and performance.

Cons: Some reviewers have found the packaging to be substandard.

Other Models to compare:

Fuel typeNatural GasNatural GasNatural Gas
GPM(Max)Up to 9.5Up to 9.0Up to 8.4
BTU input(Max)199,900 BTU/hr180,000 BTU/hr157,000 BTU/hr
Bathrooms(Max)Up to 3 – 4Up to 3Up to 2.5

2. Rheem RTG-84XLP Outdoor Tankless Water Heater:

Experience the future of hot water provision with the Rheem RTG-84XLP Outdoor Tankless Water Heater. Pioneering innovation with its Exclusive Water Savings technology. It is an exceptional unit that redefines conservation, potentially saving up to an impressive 1,100 gallons annually. Delivering a remarkable 157,000 BTUs per hour, this water heater ensures a consistent supply of warmth. It meets your needs with impressive efficiency. One of its standout features is the Exclusive Hot Start Programming. This feature intelligently minimizes the sudden cold water bursts by maintaining a ready-fire state, ensuring your comfort remains uninterrupted.

Designed to excel, it comes equipped with a recirculation pump-ready kit. The kit enables a maximum flow rate of 8.4 gallons per minute at a 35°F temperature rise. Making it able to cater to larger demands without compromise. Taking convenience to new heights, this unit is optimized for outdoor use. It comes fortified with freeze protection capabilities down to an astonishing -30 degrees. This makes it possible to safeguard performance even in the most challenging weather conditions.

Cons: Some reviewers noted that the item arrived when damaged.

3. Rheem RTGH-RH11DVLN Professional Condensing Tankless Water Heater: 

Unveiling the pinnacle of hot water innovation. The Rheem RTGH-RH11DVLN Professional Condensing Tankless Water Heater redefines instant gratification while promoting resource consciousness. Bid farewell to waiting and wastage, as this unit seamlessly provides on-demand hot water. At the same time ensuring a luxurious experience without compromising efficiency. A testament to its brilliance lies in its low operating cost, a result of its exceptional energy efficiency.

It also comes with a water savings setting that prioritizes responsible consumption. This tankless water heater’s compact and space-saving design emerges as the perfect solution in a world where space is precious. Especially for those considering a tank replacement. Safety takes center stage with its Water and gas Leak Detection feature. This intelligent safeguard not only halts operations but also offers clear error codes in the face of any irregularity.

Elevating the user experience, the Auto-Learn Programming sets a new standard. It observes water usage trends and auto-programs to meet peak hot water demands. This ensures you’re met with comfort even during busy periods. The Rheem RTGH-RH11DVLN stands as a testament to cutting-edge technology. It delivers on the commitment to enhancing your daily life with effortless warmth and efficiency.

Cons: Some reviewers experienced challenges with the flame sensor window. 

Other Models to compare:

GPM(Max)Up to 11Up to 11Up to 9.9
Fuel typeNatural GasLiquid PropaneNatural Gas
BTU input(Max)199,000 BTU/hr199,000 BTU/hr180,000 BTU/hr
Bathrooms(Max)Up to 4Up to 4Up to 3 – 4

Why Choose Rheem Electric Tankless Water Heaters?

The Rheem RTEX-18 electric tankless water heater and its counterparts stand out for several reasons. The energy efficiency, advanced technology, and comprehensive customer support make them a compelling choice. Moreover, Rheem’s commitment to innovation ensures that users get a dependable source of hot water while minimizing their environmental footprint.


1. Why my Rheem water heater not turning on?

A Rheem water heater not turning on can be attributed to a variety of factors. These range from minor issues to more complex problems. Here are a few common reasons and troubleshooting steps you can take:

  • 1. Power Supply Issues.
  • 2. Thermostat Settings
  • 3. Ignition Problems (Gas Heater)
  • 4. Overheating Protection
  • 5. Circuit Board Malfunction
  • 6. Faulty Heating Element (Electric Heater).
  • 7. Gas Supply Issues (Gas Heater).
  • 8. Ventilation Problems (Gas Heater)

If you’ve tried the basic troubleshooting steps and your Rheem water heater still doesn’t turn on, contact a professional technician. Dealing with gas and electrical systems requires expertise to ensure safety and proper resolution of the issue.

2. How to clean Rheem tankless water heater?

Cleaning your Rheem tankless water heater is essential to ensure its efficiency and longevity. Here’s a step-by-step guide on how to clean it:

Before You Begin:

  • Turn off the power supply to the water heater. For electric models, switch off the circuit breaker. 
  • Turn off the gas supply and extinguish the pilot light for gas models.

Materials You’ll Need:

  • Vinegar or a specialized descaling solution
  • Submersible pump (for flushing)
  • Bucket or drain pan
  • Hose
  • Wrench
  • Soft brush or cloth
  • Screwdriver

Cleaning Steps:

  • 1. Drain the Water Heater.
  • 2. Remove and Clean the Inlet Filter.
  • 3. Descale the Heat Exchanger.
  • 4. Flush the System.
  • 5. Reassemble and Restore Power.
  • 6. Check for Leaks.
  • 7. Regular Maintenance.

By following these steps, you can maintain the cleanliness and efficiency of your Rheem tankless water heater. This ensures a reliable and uninterrupted supply of hot water.

3. What is the best Rheem commercial water heater?

Determining the “best” Rheem commercial water heater depends on various factors. They include your specific needs, the size of your commercial establishment, the hot water demand, and the available space. However, we can provide information about a few popular Rheem commercial water heater models often considered top choices:

  • 1. Rheem GHE100-200 Universal Heavy Duty Series.
  • 2. Rheem Triton Heavy Duty Series.
  • 3. Rheem XR90 Series – Extreme Recovery Units.
  • 4. Rheem Gladiator Heavy Duty Series.

4. How much is the Rheem tankless water heater warranty?

The Rheem tankless water heater warranty can vary based on the specific model, series, and where you purchase the unit. Generally, Rheem offers different warranty periods for different components of their tankless water heaters. Here’s a general overview of what you might expect:

1. Heat Exchanger Warranty

2. Parts Warranty.

3. Labor Warranty.

We recommend checking the official Rheem website or contacting Rheem customer support. You will find accurate and up-to-date warranty information for a specific Rheem tankless water heater model here. They can provide detailed warranty information based on your chosen model and location.

5. Why is my Rheem water heater beeping?

A beeping sound from your Rheem water heater can indicate various issues or conditions requiring attention. An error code might accompany the beeping on the display panel. This can help you identify the specific problem. Here are some common reasons why your Rheem water heater might be beeping:

  • 1. Error Codes.
  • 2. Low Battery.
  • 3. Leak Detection.
  • 4. Maintenance Reminders.
  • 5. Ventilation Issues (Gas Models).
  • 6. Faulty Sensors.
  • 7. Flame Failure (Gas Models).
  • 8. System Reset.

If your Rheem water heater is beeping, the best action is to consult the user manual. It will likely include a troubleshooting section that lists possible error codes and their corresponding solutions. If the issue persists or you’re unsure, contacting Rheem customer support is recommended. A professional technician can also diagnose and address the problem safely and effectively.

Conclusion: Why We Recommend Rheem Electric Tankless Water Heaters:

Rheem Hot Water Heater has established itself as a reputable and dependable electric tankless water heater brand. The Rheem RTEX-18 electric tankless water heater has impressive features, reliability, and energy efficiency. The brand is committed to quality. Whether for residential or commercial use, Rheem’s diverse range of models makes them a top choice. This is because a solid warranty and customer service back them. When considering investing in a tankless water heater, opt for Rheem. It will translate to investing in years of consistent, energy-efficient hot water supply.

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