Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY

Rheem RTEX-13 Electric Tankless Water Heater

The Rheem Manufacturing Company was founded in 1925 in Emeryville, California. Although the brand has developed and produced a wide variety of products during their storied history, one of their most popular and enduring products is the water heater. Rheem has grown to become the largest producer of water heating products in North America, and the label has developed a loyal customer base.

Rheem tankless water heaters are among some of the most popular models currently on the market, and the newest addition to their lineup is the Rheem RTEX-13 Electric Tankless Water Heater. It is designed primarily for point of use applications. Intended for single shower applications, this hot water heater has a maximum hot water output of 3.17 gallons per minute. There is an adjustment dial on the front, allowing users to adjust the water temperature as needed. One particularly unique feature of the RTEX-13 is the inclusion of LED status lights on the front of the unit, which indicate if it is in active or standby mode.

Read on to find out more about what this top electric tankless water heater model has to offer!

Key Features

  • LED lights indicate standby mode and active element.
  • The heat exchanger is crafted from copper and brass to ensure its durability and longevity.
  • The unit has a standard half inch water connection.
  • The maximum flow rate for this model is 3.17 GPM.


  • The 4 gpm flow rate is impressive for a single shower application.
  • A sizable percentage of buyers have had the unit pay for itself within an average of 18 months.
  • The thermostat dial used for adjusting the temperature offers nine different settings.
  • The purchase of this unit includes a 6 gauge, 2 foot pre-wired power cable.


  • Rheem only offers a 1 year warranty on the parts of the RTE 13, which is considerably less than the warranties their competitors offer.
  • Due to its point of use design, the places where it can be installed in the home are limited.

Product Review

As one the best selling tankless water heaters, the Rheem RTEX-13 is a powerhouse in a compact form. It is designed to be used for point of use applications, and it will deliver hot water as needed to fixtures within a short distance of its point of installation. The nature of point of use tankless water heaters will limit where this unit can be installed; however, as long as you are able to adjust your expectations accordingly, you will be pleasantly surprised at what it has to offer.

As with other Rheem models, the RTEX-13 is equipped with low flow activation which is cutting edge technology. The minimum amount of water flow needed to activate its heater coils is .4 of a gallon per minute (gpm). This volume of water is fairly small, a little less than what you need to wash your hands. At the opposite end of the spectrum, its maximum flow rate is 3.17 gallons per minute.

Of course, the ability of any tankless electric water heater to perform is affected by the temperature of the incoming water. If the incoming water has a temperature of 55 degrees, and the desired water temperature is 105 degrees Fahrenheit, the Rheem RTEX-13 can produce up to 3.17 gallons of hot water per minute. This is more than what a showerhead would demand and it is more than sufficient to meet the demands of a kitchen or bathroom sink. If the incoming water is warmer, the flow rate of the hot water will be higher.

The Rheem RTEX-13 has an Energy Factor of .82 (according to the manufacturer). By comparison, the benchmark for an electric water heater with an affixed tank is .75 to .95.

The RTEX-13 weighs a mere 7.3 pounds and measures 12.63 x 8.25 x 3.63 inches. Because of its “ultra-compact” design, it can be installed almost anywhere in one’s home. Although the unit does come with an installation manual, Rheem will only honor the warranties it offers if the model is installed by a professional, licensed individual. Your purchase of this model includes a 2 foot, 6 gauge pre-wired power cable. It should be noted that this model is designed for indoor use only, and it should be installed vertically in a location where the water lines and the unit itself will be protected from freezing.


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Rheem has rated the RTEX-13 as capable of supplying two or three fixtures within a short distance of the installation point, making it suitable for a small condo, apartment, or home. Other alternate uses for this unit include a boat, garage, or RV tankless water heater.

Thank You For Reading

Overall, the Rheem RTEX-13 seems like an affordable, solid investment. Many online reviewers have rated it four stars or higher. Because of the factors that affect the RTEX-13’s ability to raise water temperature and its flow rate, this unit is not suitable for colder climates, but quality control issues can be minimized with special attention. When installed by a licensed water heater plumber professional and used according to the manufacturer’s recommendations, the RTEX-13 will be one of the best investments you have ever made in your home.