Rheem vs Stiebel Eltron: Tankless Water Heaters Compared by Specs
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This rheem vs stiebel eltron tankless water heater comparison focuses on two electric models. Both units provide on-demand hot water without venting. The main difference lies in their power output and control systems. Rheem offers precise digital temperature adjustment. Stiebel Eltron provides higher wattage and preset memory. You should choose based on your electrical capacity and desired temperature precision.
Key differences
| Aspect | Rheem 18kW 240V Electric Tankless Water Heater | Stiebel Eltron Tempra 29 Plus 28.8kW Tankless |
|---|---|---|
| Wattage | 18 kW | 28.8 kW |
| Flow Rate | 4.4 GPM | not listed |
| Temperature Control | ±1°F accuracy | Two memory presets |
| Dimensions | 3.5 x 14.5 x 18.5 inches | 14.5 x 16.6 x 4.63 inches |
| Weight | 14.8 pounds | 19 pounds |
Which one should you choose?
Choose Rheem 18kW 240V Electric Tankless Water Heater if
- You need precise temperature control with ±1°F accuracy.
- You have limited vertical space for installation.
- You prefer a lighter unit that is easier to handle.
Choose Stiebel Eltron Tempra 29 Plus 28.8kW Tankless if
- You require higher power output for larger households.
- You want convenient preset temperature memory options.
- You have the electrical capacity for a 28.8 kW unit.
Verdict: Choose the Rheem model if you prioritize precise temperature accuracy and a compact, lightweight design. Select the Stiebel Eltron unit if you need higher wattage and convenient preset memory features. Your decision depends on your specific electrical capacity and space constraints.
Rheem vs Stiebel Eltron Spec Breakdown
Wattage and power
Stiebel Eltron Tempra 29 Plus delivers 28,800 watts at 240 volts, while Rheem RTEX-18 provides 18,000 watts. This significant difference in electrical draw means the Stiebel unit can heat more water simultaneously. You will need three separate 40-amp breakers and 8-gauge copper wiring for the Stiebel Eltron. The Rheem model requires less electrical infrastructure, making it easier to integrate into existing circuits that may not support such high loads. Higher wattage generally supports higher flow rates during colder months.
Flow rate capacity
The Rheem RTEX-18 specifies a maximum flow rate of up to 4.4 gallons per minute. The Stiebel Eltron Tempra 29 Plus does not list a specific GPM figure in its published data. Generally, higher wattage correlates with higher potential flow, but without explicit data for the Stiebel unit, we cannot definitively compare their output volumes. You should assume the Stiebel unit has higher capacity due to its wattage, but the Rheem spec is concrete. This matters if you are running multiple showers at once.
Temperature control precision
Rheem features an external digital thermostatic control with an LED display offering ±1 degree Fahrenheit accuracy. This allows you to set the exact water temperature you need with high precision. Stiebel Eltron Tempra 29 Plus offers two temperature memory presets for personalized needs. While convenient for quick adjustments, this system does not provide the fine-grained, degree-by-degree control found in the Rheem unit. If you need precise temperature settings for sensitive skin or specific appliances, the Rheem control system is superior.
Physical dimensions
Rheem RTEX-18 measures 14.5 inches wide, 3.5 inches high, and 18.5 inches long. Stiebel Eltron Tempra 29 Plus measures 16.6 inches wide, 14.5 inches high, and 4.63 inches long. The Rheem unit is significantly flatter and thinner, which might make it easier to fit into tight spaces or low-profile cabinets. The Stiebel Eltron is taller and deeper. Both units are compact compared to tank models, but their footprints differ. You should measure your installation space carefully to ensure the specific orientation fits your available area.
Weight and installation
The Rheem RTEX-18 weighs 14.8 pounds, while the Stiebel Eltron Tempra 29 Plus weighs 19 pounds. Both units are relatively lightweight for tankless heaters, but the Rheem model is lighter. Rheem also highlights simple installation with bottom 3/4 inch NPT water connections. Stiebel Eltron requires hard-wired service and specific breaker setups. The lighter weight and potentially simpler plumbing connections of the Rheem unit may reduce installation effort. However, both require professional electrical and plumbing work due to high voltage requirements.
Which Tankless Heater Fits Your Home
Users needing precise temperature control
The Rheem model features an external digital thermostat with an LED display. It offers plus or minus 1 degree Fahrenheit accuracy. This precise control allows you to set exact water temperatures. The self-modulation technology adjusts power to meet your specific hot water demand, ensuring consistent output without sudden temperature fluctuations during use.
High-demand households requiring more flow
The Stiebel Eltron Tempra 29 Plus delivers 28,800 watts at 240 volts. This higher wattage supports greater flow rates for simultaneous use. It includes two memory presets for quick adjustments. You must ensure your home has a 200-amp service and three dedicated 40-amp breakers. This unit suits larger homes with higher hot water needs.
Those wanting simple installation and service
The Rheem unit features bottom 3/4 inch NPT water connections for straightforward plumbing. Its copper immersion heating elements are field-serviceable, simplifying maintenance. The compact design measures 14.5 by 18.5 by 3.5 inches. This model is easier to install in tight spaces and allows for simple replacement of internal components if needed.
The products compared
Rheem 18kW 240V Electric Tankless Water Heater
Best for: Whole-house electric hot water needs
- Fuel Type
- Electric
- Flow Rate
- 4.4 GPM
- Wattage
- 18 kW
- Voltage
- 240 V
- Temperature Control
- ±1°F
- Dimensions
- 3.5 x 14.5 x 18.5 inches
View on Amazon: Rheem 18kW 240V Electric Tankless Water Heater Affiliate link
The Rheem RTEX-18 is a 18 kW electric tankless water heater designed for whole-house use. It delivers up to 4.4 GPM at 240V. The unit features external digital thermostatic control with ±1°F accuracy. Its compact dimensions of 14.5 x 18.5 x 3.5 inches and 14.8 pounds weight make it easy to mount. This model suits homes with moderate hot water demands and standard electrical setups.
Pros
- 18 kW power output for whole-house service
- High flow rate of up to 4.4 GPM
- Precise temperature control with ±1°F accuracy
- Compact size measuring 14.5 x 18.5 x 3.5 inches
Cons
- Lower wattage than the 28.8 kW Stiebel Eltron Tempra 29 Plus
- Requires 240V electrical connection
- Limited to electric fuel type
Good fit if
- You need a compact unit for whole-house hot water
- You have a 240V electrical supply available
- You want precise temperature adjustments with LED display
Skip if
- You require higher flow rates than 4.4 GPM
- You need gas-powered heating options
- You want the highest available wattage for cold climates
Verdict: Rheem RTEX-18 18kW Electric Unit fits buyers who need reliable whole-house heating with precise digital control. It is ideal for standard electrical setups where space is limited.
Stiebel Eltron Tempra 29 Plus 28.8kW Tankless
Best for: High-demand whole-house electric hot water
- Fuel Type
- Electric
- Wattage
- 28.8 kW
- Voltage
- 208 V, 240 V
- Dimensions
- 14.5 x 16.6 x 4.63 in
- Use
- Whole House
- Weight
- 19 pounds
View on Amazon: Stiebel Eltron Tempra 29 Plus 28.8kW Tankless Affiliate link
The Stiebel Eltron Tempra 29 Plus delivers 28.8 kW of heating power at 240 volts. Its compact 14.5 by 16.6 inch footprint saves space without needing venting. You get two temperature memory presets for easy adjustments. This unit requires three dedicated 40 amp breakers and 200 amp home service. It suits households needing high flow rates in a small electric package.
Pros
- 28.8 kW output at 240 volts
- Compact 14.5 x 16.6 inch design
- Two temperature memory presets
- No venting required
Cons
- Requires three dedicated 40 amp breakers
- Needs 200 amp total home service
- Limited to two preset temperatures
Good fit if
- You have a 200 amp electrical service
- You need high heating capacity for multiple fixtures
- You want a compact unit without venting
Skip if
- You only have a 100 amp electrical panel
- You prefer simple single-breaker installations
- You need more than two temperature presets
Verdict: Stiebel Eltron Tempra 29 Plus fits homes with robust electrical infrastructure that demand high flow rates. It is ideal for whole-house hot water needs where space is limited.
Specifications side by side
| Spec | Rheem 18kW 240V Electric Tankless Water Heater | Stiebel Eltron Tempra 29 Plus 28.8kW Tankless |
|---|---|---|
| Fuel Type | Electric | Electric |
| Flow Rate | 4.4 GPM | not stated |
| Wattage | 18 kW | 28.8 kW |
| Voltage | 240 V | 208 V, 240 V |
| Temperature Control | ±1°F | not stated |
| Dimensions | 3.5 x 14.5 x 18.5 inches | 14.5 x 16.6 x 4.63 in |
| Use | Whole House | Whole House |
| Weight | 14.8 pounds | 19 pounds |
| Size | Small | 29 (kW) |
| Color | Gray | White |
| Model | RTEX-18 | 239223 |
Frequently asked questions
Which unit is better for a whole house with limited space?
The Rheem RTEX-18 is a compact choice for whole-house needs. It measures 14.5 inches wide and 18.5 inches long. The unit weighs only 14.8 pounds. Its small footprint allows installation in tight utility closets. You get reliable heating without taking up much room.
Can the Stiebel Eltron handle higher water flow rates?
Yes, the Stiebel Eltron Tempra 29 Plus is designed for high demand. It delivers 28,800 watts of power. This higher wattage allows it to heat more water simultaneously than lower-power units. It is ideal for homes with robust electrical infrastructure that require strong flow rates.
Do these tankless heaters require gas lines or venting?
No, both models are electric. They do not need gas lines or exhaust venting. The Rheem unit runs on 240 volts. The Stiebel Eltron also operates on 240 volts. This makes installation simpler since you only need appropriate electrical circuits rather than gas piping or ventilation ducts.
How precise is the temperature control on the Rheem model?
The Rheem RTEX-18 offers precise digital temperature adjustment. It features an external digital thermostat with an LED display. You can set exact water temperatures with plus or minus 1 degree Fahrenheit accuracy. This self-modulating system ensures consistent output without manual dial guessing.
What are the physical dimensions of the Stiebel Eltron Tempra 29 Plus?
The Stiebel Eltron Tempra 29 Plus measures 16.6 inches in width. It stands 14.5 inches tall and is 4.63 inches deep. The unit weighs 19 pounds. Its white finish blends into most utility spaces. These dimensions help you plan your installation layout effectively.
Is the Rheem heater suitable for standard electrical setups?
Yes, the Rheem RTEX-18 fits standard electrical setups. It draws 18,000 watts at 240 volts. This power level is manageable for many homes with adequate panel capacity. It is ideal for buyers who need reliable whole-house heating without requiring the heavier electrical draw of higher-kilowatt models.
Which brand offers a more compact design for the Rheem unit?
The Rheem RTEX-18 features a very compact design. Its depth is only 3.5 inches. This slim profile allows it to mount flush against walls. The gray color helps it blend into utility areas. You save space compared to bulkier water heating solutions.