Rheem Tankless Electric Water Heaters - RTEX
Review and Buying Guide
(updated 2018) 

Tankless water heaters, such as Rheem RTEX, are electric-powered products that heat water on demand and provide hot water in an endless and continuous supply. Tankless electric units are small and can be easily handled and installed, usually on the wall or under the sink, so the floor space can be used for another purpose.

As opposed to tank-type models which are subjected to standby heat loss, tankless is not prone to waste energy in such amount but can reduce the heating costs by up to 50%. The energy efficiency is usually 99% while heaters with the tank have 60-70% (depending on the model). The initial cost can be higher, but operating cost is lower and plus they last longer.

Rheem RTEX electric tankless water heaterRheem RTEX

Rheem tankless electric water heaters for the residential use are mainly designed for point-of-use, while those with more heating elements and power; 24 kW, 27 kW and up, can be used for whole-house water heating, supplying more than one fixture with hot water, even large tubs.

These models heat water instantaneously and if installed close to the fixture, it can be said that they provide hot water instantly. This is one of the reasons why they are recommended for installation as the distant units when the pipe from a central tank-type heater is too long and takes a long time to get hot water.

Electric tankless are simpler than gas tankless, cost less but produce less hot water. There are no gas burners, exhaust gases, venting, a gas line, making the installation and maintenance cheaper. If one unit cannot meet the demand of a house, then more than one unit can be installed, serving hot water either individually or combined.

Sizing

Considering the following required water flows in regards to different applications, it can be easily seen which of the provided Rheem models are point-of-use and which are for whole-house, by just looking at the flow rate (expressed in GPM).

  • Sink – 0.5 GPM
  • Dishwasher – 1-2 GPM
  • Shower - 2 GPM
  • Bath Tub – 4 GPM

In short, point-of-use models are used for the low-demand applications usually having one fixture, while whole-house water heaters are used for two or more fixtures.

Rheem RTEX model selection

Rheem tankless electric water heaters are coming from the Professional Classic series, and are available in several sizes, ranging from 3.5 kW to 36 kW models:

  • RTEX-04
  • RTEX-06
  • RTEX-08
  • RTEX-11
  • RTEX-13
  • RTEX-18
  • RTEX-24
  • RTEX-27
  • RTEX-36

RTEX-04 and RTEX-06 models are the smallest tankless electric water heaters from Rheem as they come with the power of 3.5 kW and 6 kW, generated by only one heating element and supplying one fixture with up to 1.5 GPM hot water flow. RTEX-04 and RTEX-06 are very simple models, utilizing the push-button with the ON/OFF control and the external LED temperature display to check. RTEX-04 is the only electric and tankless model from Rheem that operates using the 120V. Others require 208, 220 or 240V.

Rheem RTEX-08, RTEX-11 and RTEX-13 water heaters are larger units and can be used in both single and multi-application since the maximum water flow can reach up to 3 GPM. When comparing to the above smaller models, you will find that RTEX-08 also uses one heating element, RTEX-11 – two heating elements of 5.5 kW and RTEX-13 – two elements of 6.5 kW each. These are the only models that use side water connections.

Rheem models from RTEX-08 to RTEX-36 are all equipped with the self-modulating power control and computer logic control to meet the demand for hot water by sending the right power to the heating elements and an external adjustable digital thermostat with the LED temperature display for easy control and monitoring.

RTEX-18 tankless water heaters are designed to provide more power of up to 18 kW and water flow of 4.4 GPM. These use larger ¾” water connections, located at the bottom of the unit. The temperature of the hot water can be adjusted in the range from 80 F to 140 F using the built-in dial-knob and seen on the small screen.

RTEX-24 and RTEX-27 tankless water heaters look the same as the RTEX-18 models, utilize the same features, but have three heating elements. These models can generate 24 kW and 27 kW and produce 5.9 GPM and 6.6 GPM of hot water.

RTEX-36 is the largest tankless and electric water heater from Rheem and when compared to the above whole-house models, it has similar features but four heating elements allowing production of hot water, up to 8.8 GPM.

Summary

As it can be seen from the above overview, Rheem tankless electric water heaters are designed mainly for residential homes, either small or large, single or multiple fixtures.

They are recommended for the applications such as kitchen sinks, bathrooms, showers, tubs, washing machines, garage sinks, small offices, combined with other types, as a booster, for homes, cottages, apartments…

Keep in mind before buying any of the Rheem RTEX models, that these are indoor units and cannot be installed outside. They must be installed per codes and manufacturer recommendation for valid 5-year warranty, reliable and safe operation.

When looking at the user reviews, it is recommended to have the water flow regulator installed and control the incoming water flow and outlet temperature. As advertised and confirmed by the users, it is very easy to install, if the manufacturer’s instructions are followed. There were also some dislikes; water fluctuation for example and modification of the house, such as the installation of the new panel and electric wires.

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