Rheem vs MIZUDO: Tankless Water Heaters Compared by Specs
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The rheem vs MIZUDO tankless water heater comparison reveals two very different approaches to hot water. Rheem offers a true tankless unit designed for whole-home use, while MIZUDO provides a compact mini-tank for point-of-use applications. Both are electric, but their capacities, voltages, and intended locations differ significantly. This guide breaks down the key specifications to help you choose the right system for your home.
Key differences
| Aspect | Rheem 18kW 240V Electric Tankless Water Heater | MIZUDO 8-Gallon 120V Mini-Tank Water Heater |
|---|---|---|
| Type | Tankless | Mini-Tank |
| Use | Whole House | Under Sink |
| Capacity | Not listed | 8.0 gallons |
| Flow Rate | 4.4 GPM | Not listed |
| Voltage | 240 V | 120 V |
| Wattage | 18 kW | 1440 W |
Which one should you choose?
Choose Rheem 18kW 240V Electric Tankless Water Heater if
- You need hot water for multiple fixtures simultaneously throughout your home.
- You have a 240V electrical circuit available for installation.
- You prefer a compact unit that mounts on the wall without a storage tank.
Choose MIZUDO 8-Gallon 120V Mini-Tank Water Heater if
- You need hot water for a single sink or small appliance.
- You only have a standard 120V outlet available.
- You want a plug-in unit that fits under a sink or in a cabinet.
Verdict: Choose the Rheem if you require high flow rates for whole-home use and have the necessary electrical infrastructure. Choose the MIZUDO if you need a simple, plug-and-play solution for a single sink or point-of-use location. Your choice depends entirely on whether you need continuous flow or stored hot water for a small area.
Rheem vs MIZUDO Spec Breakdown
Intended Use
Rheem markets this unit for whole-house service, aiming to support multiple fixtures simultaneously with its 18 kW power output. In contrast, MIZUDO positions its 8-gallon mini-tank specifically for under-sink or point-of-use applications. This fundamental difference in design intent shapes every other specification. You should choose the Rheem if you need continuous hot water for showers and laundry. The MIZUDO is better suited for adding hot water to a remote bathroom, kitchen island, or office sink where a full tankless system is not practical or feasible.
Flow Capacity
The Rheem delivers a flow rate of up to 4.4 gallons per minute (GPM). This high flow supports simultaneous use, such as running a shower and a sink. The MIZUDO is a storage tank with a fixed 8.0-gallon capacity. It does not list a continuous flow rate because it relies on stored hot water. Once the tank empties, you must wait for the 1440W heating element to recover the temperature. For high-demand scenarios, the Rheem provides consistent supply. For low-demand tasks like handwashing, the MIZUDO capacity is sufficient.
Voltage Requirements
Electrical installation differs significantly between these two models. The Rheem requires a 240V circuit, which is standard for dedicated tankless water heater lines in most homes. This higher voltage allows the 18 kW element to heat water instantly. The MIZUDO operates on a standard 120V outlet. It includes an 800mm cord and requires only a 15A breaker. This makes the MIZUDO much easier to install in existing spaces without upgrading your electrical panel. If you lack a 240V line, the MIZUDO is the only viable option.
Temperature Precision
The Rheem features an external digital thermostatic control with an LED display. It offers precise temperature adjustment with an accuracy of plus or minus 1 degree Fahrenheit. This allows you to set the exact water temperature needed for specific uses. The MIZUDO includes an adjustable thermostat ranging from 55°F to 145°F. While functional, it lacks the fine-tuned digital precision of the Rheem. If you need exact temperature consistency for sensitive applications or to prevent scalding, the Rheem’s digital control provides superior accuracy.
Physical Dimensions
Size and footprint determine where you can place each unit. The Rheem is compact, measuring 3.5 x 14.5 x 18.5 inches and weighing 14.8 pounds. It mounts on a wall and takes up minimal space. The MIZUDO is larger, measuring 17.32 x 20.8 x 15.35 inches and weighing 27 pounds. It is designed to fit under sinks or cabinets. If space is extremely tight, the Rheem’s smaller profile may be advantageous. However, the MIZUDO’s dimensions are optimized for standard under-sink cabinets, whereas the Rheem requires specific wall mounting clearance.
Choose the Right Heater for Your Needs
Whole-home hot water needs
You need a true tankless solution for the entire house. The Rheem unit delivers up to 4.4 GPM at 18 kW. Its self-modulation adjusts power to meet demand. The compact 3.5-inch depth saves space. This model supports multiple fixtures simultaneously without running out of hot water.
Under-sink point-of-use installation
You require a compact unit for a sink or cabinet. The MIZUDO 8-gallon tank fits tight spaces. It plugs into a standard 120V outlet with a 15A breaker. The 1440W heating rod provides rapid recovery for handwashing and dish rinsing. It includes a CSA certification for safety.
Precise temperature control users
You want exact temperature settings. The Rheem features an external digital thermostat with ±1°F accuracy. The LED display shows current settings. You can adjust the heat precisely. This level of control ensures consistent water temperature for showers and sinks throughout your home.
RV or food truck setup
You need a portable or mobile water heater. The MIZUDO unit connects to 120V outlets and includes an 800mm cord. Its 8-gallon capacity suits small spaces like RVs or food trucks. The streamlined design fits under sinks. It provides reliable hot water for cooking and cleaning on the go.
The products compared
Rheem 18kW 240V Electric Tankless Water Heater
Best for: Small households needing precise electric hot water
- 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
This Rheem unit is a 240V, 18 kW electric tankless water heater designed for whole-house use. It delivers up to 4.4 GPM with precise temperature control accurate to ±1°F. The compact gray body measures 14.5 by 18.5 inches and weighs 14.8 pounds. You get copper immersion heating elements that self-modulate to match demand. It features a digital display and simple bottom connections for straightforward installation.
Pros
- 18 kW power output for whole-house hot water
- Precise digital temperature control with ±1°F accuracy
- Durable copper immersion heating elements
- Self-modulating technology adjusts to demand
- Compact 14.5-inch width fits tight spaces
Cons
- Requires 240V electrical circuit
- Electric model only, not gas
- 4.4 GPM may limit simultaneous use in large homes
Good fit if
- You need a compact electric heater for a single bathroom or small kitchen
- You want precise temperature control without fluctuation
- You have a 240V electrical panel ready for installation
Skip if
- You require gas fuel for higher flow rates
- You need more than 4.4 GPM for multiple simultaneous showers
- You prefer a model with remote control or smart app connectivity
Verdict: Rheem 18kW Electric Tankless Water Heater offers precise temperature control and compact design for smaller households. It fits users who prioritize stable water temperature and easy installation over high-volume flow rates.
MIZUDO 8-Gallon 120V Mini-Tank Water Heater
Best for: Under-sink hot water in tight spaces
- Fuel Type
- Electric
- Wattage
- 1440 W
- Capacity
- 8.0 gal
- Voltage
- 120 V
- Temperature Control
- 55–145°F
- Certification
- CSA
View on Amazon: MIZUDO 8-Gallon 120V Mini-Tank Water Heater Affiliate link
This 8.0-gallon electric tank heater operates on 120V power with 1440W output. Its compact dimensions of 17.32 x 20.8 x 15.35 inches fit under sinks and cabinets. You get adjustable thermostat control from 55°F to 145°F and CSA certification for safety. It is designed for point-of-use applications like handwashing and dish rinsing in tight spaces.
Pros
- Compact 8.0-gallon capacity fits under sinks
- 1440W heating rod for rapid temperature recovery
- Adjustable thermostat range from 55°F to 145°F
- CSA certified with high-temp limit shut-off
Cons
- Lower 120V voltage limits flow rate compared to whole-home units
- Small 8.0-gallon storage capacity requires recovery time
- L-shaped heating rod may be less efficient than standard designs
Good fit if
- You need hot water for a single sink or small area
- You have limited space under a counter or cabinet
- You want a plug-in installation without hardwiring
Skip if
- You need to supply hot water to multiple fixtures simultaneously
- You require high-flow rates for showers or bathtubs
- You prefer a tankless unit for endless hot water
Verdict: MIZUDO 8 Gal Mini Tank Electric Water Heater is a practical solution for under-sink hot water needs. It suits households requiring localized heating in compact spaces rather than whole-home supply.
Specifications side by side
| Spec | Rheem 18kW 240V Electric Tankless Water Heater | MIZUDO 8-Gallon 120V Mini-Tank Water Heater |
|---|---|---|
| Fuel Type | Electric | Electric |
| Flow Rate | 4.4 GPM | not stated |
| Wattage | 18 kW | 1440 W |
| Capacity | not stated | 8.0 gal |
| Voltage | 240 V | 120 V |
| Temperature Control | ±1°F | 55–145°F |
| Certification | not stated | CSA |
| Dimensions | 3.5 x 14.5 x 18.5 inches | 20.8 x 17.3 x 17.3 in |
| Use | Whole House | Camping, RV, Under Sink |
| Weight | 14.8 pounds | 27 pounds |
| Size | Small | not stated |
| Color | Gray | 8 Gal |
| Model | RTEX-18 | Etech 80 | 8.0 Gallon |
Frequently asked questions
Is the Rheem unit a true tankless heater?
Yes, the Rheem RTEX-18 is a true tankless model. It has no storage tank and heats water on demand. The unit weighs 14.8 pounds and measures 3.5 inches in depth. This compact size allows it to mount easily on a wall. It uses 18 kW of power to heat water as it flows through.
Does MIZUDO offer a tankless water heater?
No, the MIZUDO Etech 80 is a mini-tank water heater. It holds 8 gallons of pre-heated water. This is a storage unit, not a tankless system. It is designed for under-sink use. The unit is heavier at 27 pounds and takes up more space than a tankless unit.
Can the Rheem heater supply hot water for the whole house?
Rheem markets this 18 kW unit for whole-house use. It connects to a 240V electrical circuit. The high wattage allows it to support multiple fixtures. It is designed to provide consistent hot water for showers, sinks, and appliances throughout the home.
Where should I install the MIZUDO 8-gallon heater?
MIZUDO positions this unit for under-sink applications. It is best for point-of-use heating in tight spaces. The 8-gallon capacity is ideal for a single sink. It is not designed to serve the entire house. Install it close to the faucet you intend to heat.
What is the difference in voltage between these two units?
The Rheem unit requires a 240V electrical connection. The MIZUDO mini-tank operates on 120V. This voltage difference affects installation requirements. You must ensure your home has the correct circuit for the Rheem unit. The MIZUDO unit can plug into a standard outlet.
Which unit is smaller in size?
The Rheem tankless heater is more compact in depth. It measures only 3.5 inches deep. The MIZUDO unit is taller and deeper. It stands 20.8 inches high and 17.3 inches wide. The Rheem unit saves wall space, while the MIZUDO unit requires shelf or floor space.