6 Best Alternatives to the Thermomate Tankless Water Heater Electric (2026)
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You might be looking for thermomate tankless water heater electric alternatives because the original model requires significant electrical upgrades. The Thermomate 18kW unit delivers up to 4.4 GPM of hot water and fits in a compact 17.1-inch footprint. It offers precise temperature control from 80°F to 140°F in 1° increments. However, it demands a 2 x 40AMP double-pole breaker and 8AWG wiring. This high power draw and specific installation requirement may not suit every home's electrical panel or space constraints.
The 6 alternatives listed here share similar core specifications with the Thermomate. They all operate at 240V and provide 18kW of heating power for whole-house use. Some offer higher flow rates, while others provide different dimensions or smart features like WiFi. You will find options with slightly different widths or heights that may fit tighter spaces better. Each unit is selected because its technical specs overlap with the original, giving you comparable performance with varied practical benefits.
Our top pick: Thermomate 18kW Electric Tankless Water Heater.
How alternatives differ from Thermomate
NOVIEEX 18 kW 4.9 GPM Tankless Water Heater
The NOVIEEX DS-18 matches the Thermomate at 18 kW and 240V, but it pushes a higher flow rate of 4.9 GPM compared to the Thermomate’s 4.4 GPM. This makes it better for homes with strong electrical capacity that need maximum hot water volume. It shares the same indoor installation requirement and silver finish. The NOVIEEX unit is slightly more compact in width and length, measuring 11.1 inches square versus the Thermomate’s 13.1-inch width. You still need the same 240V power source. Pick this if you want higher flow without changing your electrical setup.
NOVIEEX 18kW Electric Tankless Water Heater
This NOVIEEX 18kW model is identical in specs to the other NOVIEEX option, offering 18 kW power and 240V input. It provides high flow for small-to-medium homes where space efficiency matters. Like the Thermomate, it is an indoor electric unit. The physical dimensions are 11.1 inches wide and 15.9 inches high, which is narrower than the Thermomate’s 13.1-inch width. It gives you the same power output but in a tighter footprint. Choose this if you need high flow in a smaller wall space. It does not offer smart features or WiFi connectivity, keeping the design simple and functional for consistent hot water delivery.
Rheem 18kW 240V Electric Tankless Water Heater
The Rheem RTEX-18 also runs on 18 kW at 240V, matching the Thermomate’s power level. It is designed for whole-house use with precise temperature control. The Rheem unit is taller at 18.5 inches but narrower at 14.5 inches wide, with a very thin profile of 3.5 inches. It weighs 14.8 pounds. The Rheem prioritizes durable copper components and serviceability over the compact footprint of the Thermomate. You get reliable performance for whole-house applications. Pick this if you value long-term durability and precise temperature accuracy more than the ultra-slim depth of the Thermomate. It lacks WiFi features but offers robust internal construction.
ThermoMate 14kW Electric Tankless Water Heater
The Thermomate 14kW is a lower-power version from the same brand. It runs on 14 kW at 240V, which is less than the 18 kW original. This unit is best for single-fixture applications where high flow is not needed. It is smaller, measuring 11.2 inches wide and 15.9 inches high, and weighs only 13 pounds. It saves space and energy for small areas like a bathroom sink. You give up the high flow rate of the 18kW model. Choose this if you only need hot water for one point of use. It is a practical choice for small spaces where the larger unit would be overkill.
Ranein 18kW 4.3 GPM Electric Water Heater
The Ranein RE18K offers 18 kW at 240V, similar to the Thermomate, but delivers 4.3 GPM, which is slightly lower than the Thermomate’s 4.4 GPM. It is designed for whole-house hot water with high flow needs. The unit is taller at 18.7 inches and wider at 13.8 inches, with a weight of 17.4 pounds. It provides precise temperature control for users with the necessary electrical infrastructure. You get strong performance but a larger physical footprint. Pick this if you prioritize flow consistency and have the space for a slightly bigger unit. It does not include smart features, focusing on reliable electric heating for whole-house demands.
WINTEMP 18 kW Tankless Water Heater with WiFi
The WINTEMP WN18 matches the Thermomate at 18 kW and 240V, but it adds WiFi connectivity for remote control. This is its key difference. It is designed for mild climates where remote management is useful. The unit is taller at 19.1 inches but thinner at 4 inches deep, weighing 12 pounds. You gain the ability to control settings remotely, which the Thermomate lacks. You give up the slightly more compact depth of the Thermomate. Choose this if you want smart features and remote access to your hot water settings. It is a solid option for users who value convenience and digital control alongside reliable electric heating performance.
Quick picks
Our 7 picks
Thermomate 18kW Electric Tankless Water Heater
Best for: Whole-house hot water with precise temperature control
- Fuel Type
- Electric
- Flow Rate
- Up to 4.4GMP
- Wattage
- 18kW
- Installation Location
- Indoor
- Voltage
- 240V
- Temperature Control
- 80°F to 140°F, ±1°F
View on Amazon: Thermomate 18kW Electric Tankless Water Heater
The ThermoMate ET180 delivers instant hot water at up to 4.4 GPM using 18kW of power on a 240V circuit. Its compact 17.1 x 13.1 x 3.1 inch design mounts easily on walls. You get precise temperature control from 80°F to 140°F in 1° increments. The unit features ETL certification and self-modulating technology for efficiency. It suits whole-house needs where space is tight and high flow is required.
Pros
- High flow rate of up to 4.4 GPM for whole-house use
- Precise digital temperature control in 1° increments from 80°F to 140°F
- Compact wall-mount design measuring only 3.1 inches deep
- ETL certified for safety with overheating and leakage protection
Cons
- Requires substantial electrical infrastructure including two 40A double-pole breakers
- Needs heavy-gauge 8AWG wiring for safe operation
- Indoor installation only, limiting outdoor placement options
Good fit if
- You need a high-flow unit for multiple simultaneous fixtures
- You have the electrical capacity for dual 40A breakers
- You want precise temperature adjustments in small increments
Skip if
- You cannot install dedicated 8AWG wiring and 40A breakers
- You need an outdoor-rated unit for exterior walls
- Your electrical panel lacks space for two double-pole breakers
Verdict: ThermoMate 18kW Electric Tankless Water Heater provides reliable high-volume hot water for whole-house applications. It fits buyers who have the necessary electrical upgrades and need precise temperature control in a compact footprint.
NOVIEEX 18 kW 4.9 GPM Tankless Water Heater
Best for: small homes with strong electrical capacity
- Fuel Type
- Electric
- Flow Rate
- 4.9 GPM
- Wattage
- 18kW
- Installation Location
- Indoor
- Voltage
- 240V
- Temperature Control
- 77°F to 140°F, 1°F increments
The NOVIEEX 18kW unit delivers up to 4.9 GPM at 240V, making it suitable for small to medium homes with two to three simultaneous water needs. It features an ultra-thin wall-mount design and precise 1°F temperature adjustments. This electric heater offers 99.8% thermal efficiency and includes an LED display for clear monitoring. It is built for indoor installation where space is limited.
Pros
- High flow rate of 4.9 GPM supports multiple fixtures
- Precise temperature control in 1°F increments
- Ultra-thin profile saves significant space
- 99.8% thermal efficiency reduces standby waste
Cons
- Requires 2 x 40A double-pole circuit breakers
- Needs 2 sets of 8 AWG wires
- Limited to indoor installation only
Good fit if
- You need hot water for 2-3 simultaneous uses
- You have the required 8 AWG wiring available
- You want precise 1°F temperature adjustments
Skip if
- You lack space for 2 sets of 8 AWG wires
- You cannot install 2 x 40A double-pole breakers
- You need outdoor-rated equipment
Verdict: NOVIEEX 18kW Electric Tankless Heater provides high flow and precise control for homes with adequate electrical infrastructure. It suits buyers who can support the specific wiring and breaker requirements for whole-house or multi-point use.
NOVIEEX 18kW Electric Tankless Water Heater
Best for: Small-to-medium homes needing high flow
- Fuel Type
- Electric
- Flow Rate
- 4.9 GPM
- Wattage
- 18kW
- Installation Location
- Indoor
- Voltage
- 240V
- Temperature Control
- 77°F to 140°F, 1°F steps
The NOVIEEX 18kW unit delivers up to 4.9 GPM at 240V, making it suitable for small-to-medium homes with 2-3 simultaneous fixtures. It features a slim wall-mount design and precise temperature control in 1°F steps. This electric model heats water on demand with 99.8% efficiency. You get constant warmth without scalding risks thanks to its adaptive heating system. It is a solid choice for condos or apartments needing reliable hot water.
Pros
- Delivers a high flow rate of 4.9 GPM for multiple fixtures
- Precise digital temperature control in 1°F increments from 77°F to 140°F
- Slim wall-mount profile saves space compared to storage tanks
- 99.8% thermal efficiency eliminates standby energy loss
Cons
- Requires 2 sets of 8 AWG wires and 2 × 40A double-pole circuit breakers
- Indoor installation only
- Limited to 1-year warranty coverage
Good fit if
- You need high flow for 2-3 simultaneous water uses
- You want precise temperature adjustments in 1°F steps
- You have the electrical capacity for 8 AWG wiring
Skip if
- You require outdoor installation
- Your electrical panel cannot support 2 × 40A breakers
- You need a warranty longer than 1 year
Verdict: NOVIEEX 18kW Electric Tankless Water Heater is ideal for households needing high flow and precise temperature control, provided you have the necessary 240V electrical infrastructure. It suits small-to-medium homes where space efficiency and consistent hot water are priorities.
Rheem 18kW 240V Electric Tankless Water Heater
Best for: Whole-house hot water with precise temperature control
- 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
The Rheem RTEX-18 delivers 18 kW of power at 240 volts, providing up to 4.4 GPM of hot water for whole-house use. Its external digital thermostat offers precise control with ±1°F accuracy. The unit features copper immersion heating elements and a compact footprint of 3.5 x 14.5 x 18.5 inches. It suits buyers seeking reliable, field-serviceable components and stable temperature regulation.
Pros
- 18 kW output supports up to 4.4 GPM flow rate
- External digital control with ±1°F temperature accuracy
- Durable copper immersion heating elements are field serviceable
Cons
- Heavier build at 14.8 pounds compared to lighter competitors
- Larger dimensions (18.5 inches length) require more wall space
- No remote control or smart connectivity listed in specifications
Good fit if
- You need precise temperature control for whole-house usage
- You prefer serviceable copper heating elements over sealed units
- You have space for a 14.5-inch wide installation
Skip if
- You require a compact point-of-use unit under 10 kW
- You need smart home integration or remote monitoring
- You are installing in a location with limited depth
Verdict: Rheem RTEX-18 18kW Electric Tankless is a solid choice for homeowners who prioritize precise temperature accuracy and durable, serviceable copper components over compact size or smart features.
ThermoMate 14kW Electric Tankless Water Heater
Best for: Single fixture on-demand hot water
- Fuel Type
- Electric
- Flow Rate
- 3.4 GPM
- Wattage
- 14 kW
- Installation Location
- Indoor
- Voltage
- 240 V
- Temperature Control
- 86°F to 131°F
View on Amazon: ThermoMate 14kW Electric Tankless Water Heater
This ThermoMate unit delivers 14 kW of power at 240 volts, providing up to 3.4 GPM of on-demand hot water. It features a cast aluminum heating element and smart modulation for stable temperatures between 86°F and 131°F. The compact design measures 15.9 x 11.2 x 3 inches. It suits small households or single-fixture use where lower flow rates are acceptable compared to higher-capacity alternatives.
Pros
- 14 kW output with 3.4 GPM flow rate
- Cast aluminum heating element resists scale
- Smart modulation maintains stable temperature
- Compact 15.9 x 11.2 x 3 inch size
- ETL listed for safety
Cons
- Lower 14 kW power limits simultaneous fixture use
- Requires dedicated 60 Amp circuit breaker
- Indoor installation only
Good fit if
- You need hot water for one fixture at a time
- You have space for a compact wall-mounted unit
- You want stable temperature modulation
Skip if
- You need to run multiple showers simultaneously
- You cannot install a 60 Amp double-pole breaker
- You require outdoor installation capability
Verdict: Thermomate 14kW Electric Tankless Heater offers reliable performance for single-fixture applications. It is a practical option for small spaces where high flow rates are not required.
Ranein 18kW 4.3 GPM Electric Water Heater
Best for: Whole-house hot water with high flow
- Fuel Type
- Electric
- Flow Rate
- 4.3 GPM
- Wattage
- 18 kW
- Voltage
- 240 V
- Temperature Control
- 86°F to 131°F, 1°F increments
- Certification
- CSA
The Ranein 18kW electric tankless water heater delivers up to 4.3 GPM at 240V. It supports two to three simultaneous outlets with 99% thermal efficiency. You can adjust temperature from 86°F to 131°F in 1°F increments. The compact unit measures 18.7 by 13.8 by 3.1 inches and weighs 17.4 pounds. CSA certification ensures safety standards are met for whole-house use.
Pros
- High 4.3 GPM flow rate for multiple outlets
- Precise temperature control in 1°F increments
- 99% thermal efficiency reduces standby loss
- CSA certified for safety
Cons
- Requires two dedicated 40A double-pole breakers
- Heavier than some competitors at 17.4 pounds
- No smart app or remote control listed
Good fit if
- You need high flow for whole-house use
- You want precise temperature adjustments
- You have space for a 240V installation
Skip if
- You only have a single 40A circuit available
- You prefer gas-powered heating
- You need remote control capabilities
Verdict: The Ranein 18kW Electric Tankless Heater offers strong performance for homes needing high flow rates. It suits users who prioritize precise temperature control and have the necessary electrical infrastructure installed.
WINTEMP 18 kW Tankless Water Heater with WiFi
Best for: WiFi-controlled hot water in mild climates
- Fuel Type
- Electric
- Flow Rate
- Up to 4.3 GPM
- Wattage
- 18 kW
- Voltage
- 240V
- Certification
- ETL
- Dimensions
- 19.2 x 11.1 x 4 inches
View on Amazon: WINTEMP 18 kW Tankless Water Heater with WiFi
The WINTEMP WN18 is an 18 kW electric tankless water heater rated for 240 V. It delivers up to 4.3 GPM of hot water and measures 11.1 x 19.2 x 4 inches. This model includes built-in WiFi for remote temperature adjustments. It uses self-modulating technology to adjust power based on flow. This unit suits homes in mild climates needing stable shower temperatures without waiting for preheating.
Pros
- 18 kW power output for 4.3 GPM flow
- Built-in WiFi for remote control
- Compact wall-mounted design saves space
- ETL certified for safety
Cons
- Requires 2 x 40 Amp breakers and heavy wiring
- Limited to mild to moderate climates
- Only 2-year manufacturer warranty
Good fit if
- You need remote temperature control via WiFi
- You have a 240 V electrical setup with 80 Amp capacity
- You want a compact unit for tight spaces
Skip if
- You live in a cold climate with low inlet water temps
- You cannot install dual 40 Amp breakers
- You prefer a longer warranty period than 2 years
Verdict: WINTEMP 18kW WiFi Electric Heater offers reliable hot water with convenient remote control for users with the necessary electrical infrastructure. It is a solid option for mild climates where WiFi management is a priority.
Specifications side by side
| Spec | Thermomate 18kW Electric Tankless Water Heater | NOVIEEX 18 kW 4.9 GPM Tankless Water Heater | NOVIEEX 18kW Electric Tankless Water Heater | Rheem 18kW 240V Electric Tankless Water Heater | ThermoMate 14kW Electric Tankless Water Heater | Ranein 18kW 4.3 GPM Electric Water Heater | WINTEMP 18 kW Tankless Water Heater with WiFi |
|---|---|---|---|---|---|---|---|
| Fuel Type | Electric | Electric | Electric | Electric | Electric | Electric | Electric |
| Flow Rate | Up to 4.4GMP | 4.9 GPM | 4.9 GPM | 4.4 GPM | 3.4 GPM | 4.3 GPM | Up to 4.3 GPM |
| Wattage | 18kW | 18kW | 18kW | 18 kW | 14 kW | 18 kW | 18 kW |
| Installation Location | Indoor | Indoor | Indoor | not specified | Indoor | not specified | not specified |
| Voltage | 240V | 240V | 240V | 240 V | 240 V | 240 V | 240V |
| Temperature Control | 80°F to 140°F, ±1°F | 77°F to 140°F, 1°F increments | 77°F to 140°F, 1°F steps | ±1°F | 86°F to 131°F | 86°F to 131°F, 1°F increments | not specified |
| Certification | ETL | not specified | not specified | not specified | ETL | CSA | ETL |
| Dimensions | 17.12" x 13.12" x 3.12" | 15.86" H x 11.14" W x 3.18" D | 11.14 W × 15.86 H × 3.18 D in | 3.5 x 14.5 x 18.5 inches | 15.9" x 11.2" x 3" | not specified | 19.2 x 11.1 x 4 inches |
| Use | not specified | not specified | not specified | Whole House | not specified | Whole House | Whole House |
| Features | not specified | not specified | not specified | not specified | not specified | not specified | WiFi |
| Weight | not specified | not specified | not specified | 14.8 pounds | 13 pounds | 17.4 pounds | 12 pounds |
| Size | 240V/18kW | not specified | 18 kW | Small | not specified | not specified | 18kW |
| Color | Gray | Silver | Silver | Gray | Gray | Gray | Gray |
| Model | ET180 | DS-18 | DS-18 | RTEX-18 | EH140 | RE18K | WN18 |
If you need drinking water filtration alongside heating, compare specifications for apec water apec tankless ro water alternatives.
Frequently asked questions
Can these alternatives replace the Thermomate for whole-house use?
Yes, several options support whole-house applications. The Thermomate 18kW, NOVIEEX 18kW, Rheem RTEX-18, and Ranein 18kW models are all rated for whole-house use. They provide the necessary wattage to handle multiple fixtures. If you need hot water for an entire home, these units are suitable choices that match the original capability.
Which electric tankless heater offers the highest flow rate?
The NOVIEEX 18kW model delivers the highest flow rate at 4.9 GPM. This is higher than the Thermomate 18kW, which provides 4.4 GPM. The Ranein 18kW follows with 4.3 GPM. If you require maximum water volume for showers or appliances, the NOVIEEX unit is the best option among these alternatives.
Do any of these units have WiFi connectivity?
Yes, the WINTEMP 18kW model includes WiFi connectivity. This feature allows you to control the heater remotely. Other models like the Thermomate, NOVIEEX, and Rheem do not list this feature in their specifications. If remote management is important to you, the WINTEMP unit is the only one with this capability.
What is the smallest option for a single sink?
The Thermomate 14kW is the best choice for a single fixture. It is designed for on-demand hot water in small spaces. With a lower wattage, it provides reliable performance without the high power demand of whole-house units. It is ideal if you only need hot water for one tap or a small bathroom.
Are all these heaters indoor-only units?
Yes, all listed alternatives are designed for indoor installation. The Thermomate, NOVIEEX, Rheem, and WINTEMP models specify indoor use. They require a protected environment to function correctly. You cannot install these units outdoors or in exposed areas. Ensure your installation location is dry and accessible for maintenance.
Which model has the thinnest profile for tight spaces?
The Rheem RTEX-18 has a very slim profile at 3.5 inches wide. It is significantly thinner than the Thermomate 18kW, which is 13.1 inches wide. This compact depth makes it easier to fit in narrow utility closets or behind walls. If space is limited, the Rheem unit offers the most space-efficient design.
Do these units require 240V electrical connections?
Yes, all listed electric tankless heaters require a 240V power supply. This includes the Thermomate, NOVIEEX, Rheem, and WINTEMP models. You must ensure your home has the appropriate electrical infrastructure to support these high-wattage units. Standard 120V outlets are not sufficient for these appliances. Professional installation is recommended to handle the electrical requirements.