Rheem Professional Classic RTEX Tankless Electric Water Heaters

Provide Endless Hot Water in a Durable, Space-Saving Design

Rheem RTEX-18, RTEX-24, RTEX-27, and RTEX-36 tankless electric water heaters are ideal for new construction builds and all applications in the home, including point-of-use installation. Their durable, compact design allows installation in tight spaces. In warmer climates, these models provide enough hot water to run multiple fixtures simultaneously. All RTEX models include a lifetime limited warranty. To select a unit that meets electrical and hot water gallons per minute (GPM) requirements, please use the sizing guide.

Performance Features

? Saves Space: Up to 93% smaller than a standard electric water heater.
⚡ Saves Energy: Zero standby heat loss when installed near the point-of-use.
? More Hot Water: Up to 4 times the hot water delivery of a standard electric tank (per hour).
✅ High Efficiency: UEF up to .94 and advanced self-modulating technology only consumes the power needed to satisfy hot water demand.
?️ Copper Immersion Heating Elements: Fit into a multi-chamber design to improve thermal performance, providing better temperature control and faster recovery of hot water.
? Copper Heat Exchanger: Transfers heat fast and resists corrosion.
? Durable Powder-Coated Shell: With a galvanized steel backplate.
? Brass NPT Fittings: Located on the bottom for the inlet and outlet water connections, providing strength and durability.
⬆️ Designed for Upright Mounting: With inlet and outlet water connections at the bottom of the unit for ease of installation.
?? No Venting Required: Simplifies the installation process compared to a gas tankless water heater.
? Digital Thermostatic Temperature Controls: In 1-degree increments ranging from 80°F - 140°F (26°C - 60°C).

Warranty

Limited Warranty: 5 Years for Leaks, 1 Year for Parts. Refer to the Use and Care Manual for complete information.

Certifications

These products meet a stringent set of Rheem's internally defined sustainability standards. They are AHRI Certified, ETL US Intertek certified, and tested and certified by the Water Quality Association against NSF/ANSI 372 for lead-free compliance.

Rheem RTEX Tankless Electric Water Heaters Visual Overview

The document displays four models of Rheem RTEX tankless electric water heaters: RTEX-18, RTEX-24, RTEX-27, and RTEX-36. Each unit is a compact, rectangular appliance with a white casing and a prominent red Rheem logo on the front. A digital display is visible on the upper part of each unit. The units are shown side-by-side, illustrating their uniform aesthetic. Dimensions are provided for each model, showing their compact nature: RTEX-18 (17.0" H x 13.9" W x 3.6" D), RTEX-24 (17.0" H x 17.0" W x 3.6" D), RTEX-27 (17.0" H x 17.0" W x 3.6" D), and RTEX-36 (17.0" H x 20.8" W x 3.6" D). All models share a depth of 3.6 inches and a height of 17.0 inches, with varying widths.

Tankless Electric Specifications and Minimum Requirements

DESCRIPTION	FEATURES	DIMENSIONS (SHOWN IN INCHES)
Model Number	Power (kW)	Voltage	Total Unit Amperage (AMPS)	Recommended Breaker Size	Household Electrical Service Panel Recommended	Uniform Energy Factor (UEF)	Required Wire (75°C Insulation)	Height	Width	Depth	Water Connection	# of Heating Chambers	Ship Weight (LBS.)	Heat Exchanger	Operating Pressure	Flow Activation Rate (GPM)
RTEX - 18	18	240	75	2 x 40 A Double Pole	150 AMPS	1	2 x 8 AWG*	17	14	3.635	3/4" NPT	2	14.78	Copper	Min: 25 PSI Max: 150 PSI	0.3 GPM
RTEX - 24	24	240	100	3 x 40 A Double Pole	200 AMPS	1	3 x 8 AWG*	17	17	3.625	3/4" NPT	3	17.8	Copper	Min: 25 PSI Max: 150 PSI	0.3 GPM
RTEX - 27	27	240	113	3 x 40 A Double Pole	200 AMPS	1	3 x 8 AWG*	17	17	3.625	3/4" NPT	3	17.8	Copper	Min: 25 PSI Max: 150 PSI	0.3 GPM
RTEX - 36	36	240	150	4 x 40 A Double Pole	300 AMPS	1	4 x 8 AWG*	17	21	3.625	3/4" NPT	4	22.7	Copper	Min: 25 PSI Max: 150 PSI	0.3 GPM

NOTE: When converting from an electric tank to an electric tankless water heater, household electric service panel upgrades are often required. Please see the electric service panel recommendations above.

*AWG - American Wire Gauge

Sizing a Tankless Electric Water Heater

IMPORTANT: Verify that your home meets the electrical requirements. See specifications and minimum requirements.

Step 1: Estimate Your Total Household Gallons Per Minute (GPM) Needs

Estimate your total household gallons per minute (GPM) needs by adding up the average flow rates by fixture (showers, faucets, dishwasher, washing machine) that run at the same time.

Example: 1 shower and 1 kitchen faucet running at the same time adds up to 3.5 GPM (2 + 1.5 = 3.5 GPM).

Average Flow Rates (GPM) by Fixture

Fixture	GPM
Low Flow Faucet	0.5
Bathroom Faucet	1
Kitchen Faucet	1.5
Shower	2
Dishwasher	2
Washing Machine	3

Flow rates may vary.

Step 2: Locate Your Zone on the Map

U.S. Average Ground Water Temperature Zone Map

A color-coded map of the U.S. shows average ground water temperature zones, ranging from colder temperatures in the north (blue) to warmer temperatures in the south (red). The map includes regions for Canada (CAN), Alaska (AK), Hawaii (HI), and Puerto Rico (PR), indicating varying ground water temperatures across these areas.

Step 3: Select the Model That Can Supply Your Estimated Total Household GPM with Your Ground Water Temperature Zone

Flow Rate Capacity Table by Zone (Gallons Per Minute - GPM)

Model #	Zone 1 37°F/3°C	Zone 2 42°F/5°C	Zone 3 47°F/8°C	Zone 4 52°F/11°C	Zone 5 57°F/14°C	Zone 6 62°F/17°C	Zone 7 67°F/20°C	Zone 8 72°F/22°C	Zone 9 77°F/28°C
RTEX - 18	1.8	2.0	2.1	2.3	2.6	2.9	3.2	3.7	4.4
RTEX - 24	2.4	2.6	2.8	3.1	3.4	3.8	4.3	5.0	5.9
RTEX - 27	2.7	2.9	3.2	3.5	3.8	4.3	4.9	5.6	6.6
RTEX - 36	3.6	3.9	4.2	4.6	5.1	5.7	6.5	7.5	8.8

Flow rates are calculated to a set point of 105°F. Ground water temperature varies seasonally.

OPTIONAL - Flow Regulator Sizing Table by Zone (Gallons Per Minute – GPM)

The flow regulator fitting threads onto the outlet water connection and limits the outlet flow to the GPM specified in the table. Select the appropriate GPM insert for your model based on your zone. This is an optional part to ensure accurate temperature output.

Model #	kW	Connection Size	Part #	Zone 1 37°F/3°C	Zone 2/3 42-47°F/5-8°C	Zone 4/5 52-57°F/11-14°C	Zone 6/7 62-67°F/17-20°C	Zone 8/9 72-77°F/22-28°C
RTEX - 18	18	3/4" NPT	IFR 3-4	2.0	2.0	2.0	3.0	3.0
RTEX - 24	24	3/4" NPT	IFR 3-4	2.0	2.0	3.0	3.0	4.0
RTEX - 27	27	3/4" NPT	IFR 3-4	2.0	2.0	3.0	4.0	5.0
RTEX - 36	36	3/4" NPT	IFR 3-4	3.0	4.0	4.0	5.0	-

NOTE: (-) indicates flow regulator insert is not recommended in this zone.

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