Rheem RTEX-18 18kW 240V Electric Tankless Water Heater

Home » Rheem RTEX-18 18kW 240V Electric Tankless Water Heater

If you’re looking for a new electric tankless water heater, read our Rheem RTEX-18 review. These are specially designed to save your electric bills, but to do that, you need to choose a proper size (strength) depending on your household and water usage. In case you decide to go with a more powerful unit, check this RTEX-24 review.

A tankless water heater delivers hot water on demand, which is why they declare specified GPM (Galon Per Minute). By heating a water flow, instead of water in a tank, these are supposed to save your electric bills, giving you certain money-saving through the time. Rheem company provides a variety of models, you can choose from. It is important to choose an appropriate unit for your home so that the whole family can use showers and baths as they need to.

Rheem RTEX-18 is a model that gained a lot of attention from all around States. This is why we are writing this Rheem RTEX-18 review. We’ll try to give you a deeper insight into this tankless water heater. Find out its specifications, installing options, and look for a proper model of tankless water heater for your home.

Rheem RTEX-18 review
Rheem RTEX-18 tankless electric water heater

The Rheem RTEX 18 model is equipped with a rugged copper and brass heat exchanger. It has been designed so it could withstand harsh water conditions. This heater ensures longevity, compactness, and usability because its installation process is simple and it is slim, and lightweight.

Due to its space-saving design, you can install it at any nook and corner. It installs easily and RTEX-18 won’t disturb your space no matter where you have put it. Rheem RTEX-18 heats water only when demanded, and it is energy efficient. This particular model Rheem RTEX-18 is a classic series of professional water heaters suitable for residential use. It uses the power of 240V to power up 2 heating chambers. An RTEX-18 tankless water heater can deliver continuous hot water on-demand for single point-of-use or multiple applications.

Additional convenience comes from its on-unit control system that allows easy temperature adjustments. On average this tankless water heater provides up to 5.0 GPM water and this unit is appropriate for two bathrooms in hot weather and one bathroom in cold climates. It is an ideal choice as a point-of-use application and the perfect choice for homes, condos, apartments, hospitals, offices, boats, hotels, and restaurants.

RTEX-18 heating chambers
Rheem RTEX-18

Rheem professional classic series RTEX-18 tankless electric water heaters offer continuous hot water quick on-demand for single point-of-use or multiple applications.

Rheem RTEX-18 Features

  • Modulating power and On-Unit temperature controlling feature
  • Brass/Copper heat exchanger
  • Standby mode
  • LEDs indicate active element
  • Regular 1/2inches water connectivity
  • Around 3.51GPM constant flow of water guaranteed at 35degree Fahrenheit
  • Suitable for two bathrooms during summers and one bathroom during winters
  • 18KW heater requires a 240V electrical connection, two 40amp circuit breakers and 8gauge copper wiring
  • An energy-efficient heater that warms water only when demanded
  • Space-saving and lightweight product
  • One year parts warranty, ten years heat exchanger warranty

Performance RTEX-18 Features

On-demand, consistent, and endless hot water
Compact and stylish with digital temperature control in increments of 1°F ranging from 80°F to 140°F
99.8% Energy efficient
Robust copper immersion heating elements with brass top increases durability
Simple Installation
Digital temperature display
External controls to adjust the temperature in increments of 1°F

Applications and dimension

Rheem RTEX-18 applications

Whole-Home – up to 6 GPM
Water-Saver Shower Head – 1.5 GPM
Standard Shower Head – 2.0 GPM
Standard Hand Sink – 0.5 GPM
Kitchen Sink – 1 to 2 GPM
Bath Tub – = 4 GPM
Dishwasher – 1 to 2 GPM
Washing Machine – 1 to 1.5 GPM

This unit is compact and stylish, appropriate for residential homes. It comes with cool-looking digital temperature control in increments of 1°F ranging from 80°F to 140°F.

Read about Rheem vs. AO Smith if you like.

Rheem RTEX-18 dimensions

Item Dimensions LxWxH: 18.25 x 3.5 x 14.5 inches

Rheem rtex 18 dimensions
RTEX-18 dimensions


This tankless water heater does its job well. To use it in your home you’ll need two 40amp breakers. It is recommended to hire a professional to install it in your home. Before a final decision, be sure to choose an appropriate unit. The RTEX-18 should be enough for most homes. A highly energy-efficient device heats water when you demand it and therefore, it can reduce your regular electricity bills. The on-Unit controlling feature helps in adjusting the temperature. Easy to install and stylish design that fits virtually anywhere. This is a very reliable heating solution because there are no apparent complaints about leakage.