Rheem RTEX 18 Review


The Rheem RTEX 18 model is equipped with a rugged copper and brass heat exchanger, which can withstand harsh water conditions. This heater ensures longevity, compactness and usability because its installation process is simple and it is slim and light weight. Due to its space saving design, you can install it at any nook and corner. Since RTE 18 heats water only when demanded therefore, its energy consumption is very low. Additional convenience is offered by 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 during cold climate. It is an ideal choice as a point-of-use application and perfect choice for homes, condos, apartments, hospitals, offices, boats, hotels and restaurants.


  • 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
  • Energy efficient heater that warms water only when demanded
  • Space saving and light weight product
  • One year parts warranty, ten years heat exchanger warranty

The Pros & Cons of the Rheem RTEX 18


  • Highly energy efficient because it heats water when you demand it and therefore, it can reduce your regular electricity bills
  • Maximum flow rate offered is % gallons per minute, which is outstanding
  • On-Unit controlling feature helps in adjusting temperature
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    Easy to install and stylish design that fits virtually anywhere
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    This is a very reliable heating solution because there are no apparent complaints about leakage


  • This heater is not as easy to be installed by a novice simply because the unit doesn’t come with a user manual
  • Warranty is insufficient and many users complain about the short life of the heater and poor quality parts
  • Consumes lot of energy and while it is operating other energy consuming devices such as light bulbs start flickering
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    It is advertised that this model can supply hot water to two bathrooms but in reality if both shower and sink are in use then water becomes cold sooner than expected


Assembled Depth3.25"
Assembled Height10.50"
Assembled Width11.25"
Water Connection Size1/2
Amperage (amps)75
Electric Product TypePoint of use
Finish FamilyGray
Color FamilyBlack,Blacks
Flow Rate @ 35 F Rise (gallons/min)3.51 gal (US)/min
Flow Rate @ 45 F Rise (gallons/min)2.73 gal (US)/min
Maximum Temperature (F)125
Minimum Activation Rate (gpm)0.4
Power/Fuel TypeElectric
Fuel TypeElectric
Wattage (watts)1500
Product Weight (lb.)12 lb
Residential/Commercial/industrial UseResidential or Comercial
Modelrte 18
Water Connection LocationSide
Wattage (watts)18000


This tankless water heater does its job well but finding its parts becomes a bit difficult after a while. Another drawback is that it requires two 40amp breakers. This makes it a bad choice if saving energy is your top priority as the unit will consume a lot of energy. Buy it if you require plenty of hot water or have a bigger family.

You can buy the Rheem RTEX 18 on Amazon.

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