Rheem RTEX 13 Electric Tankless Water Heater Review

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Rheem is an American manufacturing company which is a subsidiary of Paloma Industries.

It was founded in 1925 and is currently headquartered in Atlanta, Georgia, United States. Rheem is the biggest manufacturer of water heating products in the US and Canada.

The Rheem RTEX 13 is a tankless electric water heater that is ideal for single point-of-use or multiple applications. It is 99.8% energy efficient and supplies continuous hot water to its connected fixtures.

It is compact enough to be installed under a sink or cabinet and is excellent for installation in RVs.

Key Specifications of Rheem RTEX 13

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

The Rheem RTEX-13 has an energy efficiency of 99.8%. It has a digital temperature display that can be adjusted in increments of 1˚F. Temperature settings range from 80˚F to 140˚F.

It has copper heating elements with brass tops that improve the durability of the heater. The heating elements are also threaded for hassle-free replacement.

It has a maximum flow rate of 4.8 GPM, and it is capable of producing a temperature rise of 30˚F at this flow rate.

This is an electric tankless water heater meant for indoor installation.

Specification Table

The specifications are summarised in the below table – 

Parameter Specification
Dimensions 12.63" H × 8.25" W × 3.63" D
Weight 8.5 lbs
Energy Factor 0.99
Water connections ½" NPT
Voltage 240 V
Power 13 kW
Current 54 A
Recommended breaker 60 A
Recommended wire 6 AWG
Minimum flow rate 0.3 GPM
Maximum flow rate 4.8 GPM
Pressure Minimum 25 psi
Pressure Maximum 150 psi


Prior to installation, read the instructions provided in the user manual carefully to avoid injury to self or damage to the product.

The installation location should be chosen such that the product is protected from freezing temperatures and also easy to access.

Ensure that the heater is kept away from materials that can hinder its operation. Mounting can be done easily due to its built-in mounting brackets.

For the plumbing and the electrical installations, Rheem recommends hiring trained professionals in those respective fields to complete the tasks.

Follow the installation steps carefully and make sure that the installation is in accordance with the local or state codes.

Set the temperature on the panel with the help of the sizing guide provided in the manual. Finally, choose a flow regulator to go with your water heater.

Although the outlet flow regulator is optional, it greatly enhances the performance of the water heater.



Rheem provides a limited warranty for all its products. The heating chamber has a warranty period of 5 years, whereas, the other parts of the heater have a 1-year warranty term.

The effective warranty period starts from the date of installation (with proof), or 90 days from the date of manufacture.

Although the warranty is applicable to the tank and other parts of the heater, there are some limitations to what it covers. These limitations are listed below.

  • Service trips to your home.
  • If any product damage occurs due to improper installation or maintenance.
  • If product failure occurs due to improper sizing of the water heater lines or the electrical connections.
  • Damages due to unauthorized removal or addition of heater parts.
  • Tank failure due to exposure to corrosive materials or due to the use of water that is not potable.
  • Damages due to accidents or any other causes that are not directly influenced by manufacturing defects.
  • Subjecting the heater to conditions beyond its specified limits.
  • Installing the heater outside the US.

To claim the warranty, first, determine if the product is still ‘in-warranty’.

If the period has not expired, contact the contractor who had the product installed. Another option is to contact Rheem by telephone – (800)622-5622 or through their website – www.rheem.com

Care and Maintenance

For the heater to perform efficiently, not only should the setup be done properly, but the heater should be maintained appropriately as well.

One of the primary considerations required before installing this product is the water quality in the area. Go through the chart for recommended water quality levels provided by Rheem.

Consider installing a water softener in areas with very hard water.

The connection to the water heater should be checked at least once every year for leaks and other damages. Do not overtighten the connections as this could lead to serious internal damage to the heater.

Do not proceed with the maintenance tasks until the power to the heater has been shut off. Purge the pipelines to get rid of any air in them before bringing the power back on.

Maintenance should be done more frequently for units installed in places with very high levels of mineralization in the water.


Consumer Comments

People who have bought Rheem RTEX 13 electric tankless water heater have vouched for the energy and money savings that come with its use. Some users have recorded up to 30% savings in heating bills.

The compact size of the heater has also allowed for its installation in any place that the user desires. The water comes out pretty fast and in the constant temperature in a household of one or two.

In bigger households, users have installed the heater in single bathrooms.

People also prefer this product for single-point uses that require a large amount of water. Also, customers are finding the digital temperature display and its control rather convenient to use.

With this, the temperature can be set quite easily.

One other factor that has immensely satisfied the customers is the customer support provided by Rheem.

People have stated that damaged parts are repaired or replaced by the manufacturer under warranty pretty fast, and without any issues.

Some customers, however, have been critical of this product because of its incapability to supply hot water to multiple fixtures at the same time. This can be avoided by the proper sizing of the water heater before installation.



  • It has an energy efficiency of 99.8% which also results in savings in heating cost for the user.
  • It provides a fast supply of hot water to the fixtures as it is commonly used for point-of-use applications.
  • Its compact size allows for its installation in cabinets and underwater sinks. It also does not require any venting as it is an electric heater.
  • It has a digital temperature control that can be adjusted in increments of 1˚F. This makes its operation very simple.
  • The heating element is copper with brass caps that improves the durability of the product. It can also be replaced easily.


  • Flow rate is quite low for whole-house installations.
  • Cannot be used for various applications at the same time without a drop in the hot water temperature.
  • Modification of the home’s electricity to supply 240 V and 60 A might be necessary.


Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY
594 Reviews
Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY
  • External adjustable digital thermostatic control with LED display (+/1 degree accuracy
  • Durable Copper immersion two heating elements, field Serviceable.Self-modulating power control
  • Simple installation – 1/2 NPT adapters included; side 1/2 inch Compression water connections

Our Recommendation

The Rheem RTEX 13 is a highly efficient electric tankless water heater that can be easily installed and maintained.

Apart from saving energy, it also significantly helps in saving a lot of money on utility bills. This tankless heater is very compact and can be installed in the smallest of spaces.

It has a modest flow rate of a maximum of 4.8 GPM which makes its installation in small homes and RVs practical.

However, it is capable of performing optimally when installed for single bathrooms or point-of-use applications that require a large amount of water.

For users who are looking to buy a compact water heater that is easy to operate and helps in saving energy as well as money, the Rheem RTEX 13 is the right choice.

Recommended Accessories

Service Valve Kit Rheem RTG20220AB Webstone Tankless Water Heater Service Valve Kit, Clean Brass


Remote Control Rheem RTG20006DW Main Control



How many Amps are Needed for this Product?

The Rheem RTEX 13 electric tankless water heater requires 54A and a 1×60A breaker at 240V. The recommended wire size is 6 AWG.

Can this Water Heater be Returned if I have any Problems?

If the water heater is damaged on arrival or during purchase, you can return the product to the supplier. If you face any problems with the supplier, the warranty terms may be applied by contacting the manufacturer.

Can this unit be Installed lying on its back Rather than Upright on a wall?

No. This product is meant for wall-mounted installations only. It should always be kept in an upright position. Do not attempt to fix this product in any other positions.

What is the Warranty?

The heating chamber has a warranty period of 5 years whereas the other parts have a warranty period of 1 year. The warranty period starts from the date of installation.


The Rheem RTEX 13 electric tankless water heater is an energy-efficient and compact water heater with an Energy Factor of 0.99. It is not only easy to install, but its digital temperature control makes it highly convenient to operate as well.

Due to its small build, maintaining the water heater also does not require much effort.

This water heater has a moderate output flow rate, making it one of the best choices for point-of-use application and also for small homes or recreational vehicles.

Last update on 2022-12-01 / Affiliate links / Images from Amazon Product Advertising API

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