Rheem RTEX 13 Electric Tankless Water Heater Review

The RTEX 13 electric tankless water heater is designed for point of use application and features an innovative space saving design that’s perfect for homeowners who are short on space. This model will only heat up water as needed, which in turn allows the user to save both energy and water. This model is perfect for single shower applications and can provide hot water at an impressive rate of four gallons per minute.

RTEX Tankless Water Heater Overview

This model by Rheem utilizes a rugged copper and brass heat exchange, allowing you to easily achieve the desired heating results. Copper actually offers higher thermal conductivity when compared to most metals. It is able to quickly conduct heat, distributing it evenly. Copper is also impressively corrosion resistant.

This tankless water heater requires a six gauge wire and sixty amp breaker for optimal performance. 0.4 GPM is the minimum flow rate needed to activate the heating system. In order to maintain constant output at the ideal temp, this tankless model is equipped with modulating power control.

On the front of the appliance you’ll find a temperature adjustment dial, which will allow you to set the desired water temp. This model also features brightly lit LED status lights that display whether the unit is in active or standby mode. These lights can also tell you if the elements are energized.

This 13,000 watt water heater utilizes the standard ½” water connection. Both the hot and cold water connections are found on the side of the water heater. Most consumers felt that the water tank was very easy to install, for those with some prior experience.

This model measures in at just 7.5 inches in length by 7.5 inches in width and 7.5 inches in height. Due to its compact design it can be paired with pretty much any appliance in the home, such as a dishwasher, washer or kitchen sink.

Because it runs on electricity, there will always be hot water available, almost instantly. Even better, since it doesn’t store hot water in a container, it doesn’t have to keep on using electricity in order to maintain hot temperatures continuously. While hot water will always be available, you’ll still be able to reduce your monthly electric bill costs.

Even though most water heater lines are 5/8”, this model uses the standard ½” water lines with compression fittings. You’ll need at least eighteen inches of copper pipe for both the cold and hot water lines running through the unit, because these lengths will provide the necessary grounding. Because of this you shouldn’t use quick connectors or flexible piping. Again, you should leave the installation to a licensed pro.

For improved safety and flexibility, you should have shutoff valves installed on the water lines. In order to avoid fluctuations in water temperature, make sure you purge any air from the lines during installation. In order to maximize performance you can adjust the water inflow at each water outlet. Make sure you allow the water to run and adjust the incoming hot water flow to the mid-point. Next, adjust the mix of cold and hot water flow to the desired level.

The manufacturer offers a one year product warranty on parts and a ten year warranty on the heat exchanger. These warranties will only remain valid if you have the unit installed by a professional electrician.

The manufacturer has rated this model for two to three fixtures on a short run from the installation point, making it perfect for smaller homes.  The water flow and temperature rise works well for a kitchen, single bathroom or laundry room. The RTEX 13 is only rated for indoor use and must be installed vertically, in a location that’s dry and where the water lines are well protected against potential freeze. The manufacturer also recommends that the water heater be installed as close as possible to the appliance with the greatest demand for water, such as a washing machine.

It’s important that the amount of electricity that’s supplied to the unit meets the power demands, otherwise its performance will be negatively affected.

Tankless Water Heater Pros and Cons


The manufacturer provides innovative low flow activation technology, which is a big selling point for this model. For many homeowners, the size of a water tank can be a big concern. A tank model is generally much larger than their tankless counterpart and because of this many consumers opt for these compact models, which allows them to save a ton of space.  Many consumers reported saving an average of thirty to forty dollars a month on their energy bill.


While some consumers have stated that the installation process was a breeze, consumers with no prior experience should have this unit professionally installed by a licensed electrician, so you’ll need to factor in the extra cost of hiring an electrician for the installation process. Improper installation can result in poor performance. Consumers who have tried to install this model on their own usually fail to ground it properly.

In order for the warranties to remain valid, you’ll need to have a pro do the install and you must mail in documentation to the manufacturer that can prove the unit was professionally installed.

While the manufacturer mentions nothing about the tank’s maintenance needs, you’ll want to install a water filter in order to prevent mineral scale build-up.

Other consumer complaints included issues with the non-standard hot water connections, challenging installation and the compression fittings. This model draws up to fifty-four amps when in use, which some consumers found excessive. Other consumers complained that they were unable to use more than one appliance at a time, without experiencing annoying low water flow. Consumers who need a more powerful model can check out the ECO 27 Eco Smart electric tankless water heater.

Electric Tankless Water Heater Conclusion and Rating

This model works well for smaller spaces, just don’t get your hopes up in terms of power and usage abilities. The manufacturer clearly states what this tankless water heater can do, so it’s important that you closely follow the usage guidelines. Affordable, dependable and durable, consumers gave this model a rating of four out of five stars.