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Finding the best tankless water heaters with tankless designs requires looking at specific output ratings and physical dimensions. We compared 15 units using only the specifications published on their listings. The Rheem 18kW 240V Electric Tankless Water Heater leads because its 14.5-inch width fits tight spaces better than most competitors. This guide helps you decide which unit matches your home’s electrical capacity and flow needs.
01 Match flow rate to your fixture count
Choose based on how many fixtures run at once. Single-sink units like the Orbek 14kW handle one station. Whole-house models like the Rinnai 11.1 GPM support multiple bathrooms. Check the gallons per minute or kilowatt rating. Ensure your electrical or gas service matches the unit's requirements before buying.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | Rheem 18kW 240V Electric Tankless Water Heater Best overall | small homes needing compact electric heating | |
| 2 | Thermomate 18kW Electric Tankless Water Heater Also great | Single shower indoor use | |
| 3 | Westinghouse 24kW WiFi Tankless Water Heater Also great | Whole-house electric hot water with smart control | |
| 4 | VancEpic 4.8 GPM Natural Gas Tankless Heater Best child safety lock | whole-house natural gas hot water needs | |
| 5 | Stiebel Eltron Tempra 29 Plus 28.8kW Tankless Also great | whole-house hot water with strong electrical service | |
| 6 | Ranein 4.3 GPM Indoor Propane Tankless Water Heater Also great | Whole-home propane heating for 3-4 fixtures | |
| 7 | Rinnai 11.1 GPM Condensing Dual-Fuel Water Heater Best premium | large households needing high flow rates | |
| 8 | Orbek 14kW 240V Tankless Water Heater Best budget | single sink or shower applications | |
| 9 | WINTEMP 36kW Electric Tankless Water Heater Also great | Whole-house hot water with high flow needs | |
| 10 | APUS 95,000 BTU 4.42 GPM Indoor Propane Heater Also great | Indoor propane heating for 2–3 fixtures | |
| 11 | WINTEMP 11kW 240V Electric Tankless Water Heater Best compact | single sink or small shower point-of-use | |
| 12 | ThermoMate 4 GPM Propane Tankless Water Heater Best bathroom | Bathroom single fixture use | |
| 13 | APUS 18kW 4.4 GPM Tankless Water Heater Also great | Whole-house hot water for 2-3 fixtures | |
| 14 | Ranein 18kW 4.3 GPM Electric Water Heater Also great | Whole-house electric hot water with precise temp control | |
| 15 | SIVUATEK 14kW 240V Electric Tankless Water Heater Also great | single sink or shower applications |
02 The best fit for you
- You want the best overall compact electric heater – Rheem 18kW 240V Electric Tankless Water Heater – Its 14.5 by 3.5 inch size fits tight spaces better than other electric models.
- You need high flow for large households – Rinnai 11.1 GPM Condensing Dual-Fuel Water Heater – This unit delivers 11.1 GPM, the highest flow rate on the list.
- You want the most compact unit available – WINTEMP 11kW 240V Electric Tankless Water Heater – Weighing only 8.6 pounds, it is the lightest and smallest model here.
- You need whole-house propane heating – Ranein 4.3 GPM Indoor Propane Tankless Water Heater – It provides 4.3 GPM flow for whole-home use on propane fuel.
Rheem 18kW 240V Electric Tankless Water Heater
Best for: small homes needing compact electric heating
- Features
- Tankless
- Fuel Type
- Electric
- Max Flow Rate
- up to 4.4 GPM
- Heating Capacity
- 18kW
- Voltage
- 240V
- Wattage
- 18 kW
The Rheem RTEX-18 is a compact, wall-mounted electric tankless water heater designed for whole-home use. It delivers up to 4.4 gallons per minute at 18kW power. The unit features an external digital thermostat with LED display for precise temperature control. Its small footprint and lightweight build make it easy to install in tight spaces. You get durable copper immersion heating elements that are field-serviceable. This model suits households needing reliable hot water without a bulky storage tank.
- 18kW heating capacity provides up to 4.4 GPM flow rate
- Compact dimensions: 18.5 inches long by 3.5 inches high
- External digital thermostatic control with LED display
- Lightweight design at 14.8 pounds
- Durable copper immersion heating elements
- 18kW power is lower than the 24kW and 36kW electric options on the list
- 4.4 GPM flow rate is lower than gas models offering 4.3 to 11.1 GPM
- Single voltage requirement of 240V limits compatibility compared to multi-voltage units
- You need a compact unit for a small home or apartment
- You want precise temperature control via a digital display
- You have a 240V electrical circuit available for installation
- You require a flow rate higher than 4.4 GPM for multiple simultaneous showers
- You prefer gas heating for lower operating costs or higher capacity
- You need a unit with WiFi connectivity for remote control
Verdict: Rheem RTEX-18 18kW Electric Tankless is a solid choice for small households prioritizing compact size and digital precision over maximum flow rate. It fits well in tight spaces where larger electric or gas units cannot go.
Thermomate 18kW Electric Tankless Water Heater
Best for: Single shower indoor use
- Features
- Tankless
- Fuel Type
- Electric
- Max Flow Rate
- Up to 4.4GMP
- Heating Capacity
- 18kW
- Installation Location
- Indoor
- Voltage
- 240 Volt
The ThermoMate ET180 is a 240-volt electric tankless water heater designed for indoor use. It delivers up to 4.4 GPM with an 18kW heating capacity. The unit features a digital display allowing temperature adjustments from 80°F to 140°F. Its compact dimensions of 17.1 by 13.1 inches save space. This model suits households needing reliable on-demand hot water for showers.
- 18kW heating capacity for steady hot water
- Max flow rate of 4.4 GPM
- Digital display with 1°F increments
- ETL certified for safety
- Self-modulating energy technology
- 18kW power is lower than 24kW or 36kW competitors
- Requires two 40A double-pole breakers
- 4.4 GPM is lower than 11.1 GPM gas models
- You need a compact indoor electric unit
- You want precise temperature control
- You have the required electrical capacity
- You need high flow for multiple showers
- You prefer gas fuel sources
- You lack space for 17.1 inch height
Verdict: ThermoMate 18kW Electric Tankless Heater offers steady performance for single-station use. It fits homes with adequate 240V electrical infrastructure.
Westinghouse 24kW WiFi Tankless Water Heater
Best for: Whole-house electric hot water with smart control
- Features
- Tankless
- Fuel Type
- Electric
- Max Flow Rate
- 5.55 GPM
- Heating Capacity
- 24 kW
- Voltage
- 240 V
- Fixture Capacity
- Shower and sink
This Westinghouse unit delivers 5.55 GPM at 24kW for whole-house use. It supports simultaneous shower and sink use with a wide temperature range of 86 to 140°F. Smart WiFi lets you control settings via app or voice commands. The compact 17.1-inch height saves space. It requires a 100A circuit and 240V power for operation.
- High 5.55 GPM flow rate for whole-house demand
- Smart WiFi and voice control integration
- Compact 17.1-inch height saves wall space
- Wide 86-140°F temperature adjustment range
- Requires a heavy 100A electrical circuit
- Lower flow rate than gas competitors on this list
- Heavier 17-pound build than smaller units
- You need whole-house hot water for multiple fixtures
- You want remote temperature control via smartphone
- You have the electrical capacity for a 100A breaker
- You only have a 40A or 60A electrical panel
- You prefer gas heating over electric resistance
- You need a flow rate above 5.55 GPM
Verdict: Westinghouse 24kW Electric Tankless Water Heater fits homes that can support high amperage and need reliable whole-house coverage. It offers smart convenience and strong flow for simultaneous use.
VancEpic 4.8 GPM Natural Gas Tankless Heater
Best for: whole-house natural gas hot water needs
- Features
- Tankless, Child Safety Lock, LED Display
- Fuel Type
- Natural Gas
- Max Flow Rate
- 4.8 GPM
- Heating Capacity
- 110,000 BTU
- Installation Location
- Indoor
- Fixture Capacity
- 3-5 water outlets
The VancEpic 110,000 BTU natural gas unit delivers 4.8 GPM for whole-house use. It features an oxygen-free copper heat exchanger and ±1°F temperature control. The design includes a child safety lock and quiet operation. This indoor heater supports 3-5 water outlets. It suits families needing stable hot water flow without sudden temperature changes.
- 110,000 BTU heating capacity
- 4.8 GPM continuous flow rate
- Child safety lock included
- Oxygen-free copper heat exchanger
- ±1°F precise temperature control
- 2-year warranty is shorter than typical industry standards
- Indoor-only installation limits placement options
- Non-condensing design may have lower efficiency than condensing models
- You need a natural gas heater for whole-house use
- You want precise temperature control within ±1°F
- You require a child safety lock for family homes
- You need outdoor installation capability
- You prefer condensing technology for higher efficiency
- You require a warranty longer than 2 years
Verdict: VancEpic 110,000 BTU Natural Gas Heater provides reliable whole-house hot water for families who value precise temperature stability and child safety features.
Stiebel Eltron Tempra 29 Plus 28.8kW Tankless
Best for: whole-house hot water with strong electrical service
- Features
- Tankless
- Fuel Type
- Electric
- Heating Capacity
- 28.8kW
- Voltage
- 240 or 208-volt
- Intended Use
- Home
- Dimensions
- 4.63 × 16.6 × 14.5 inches
This Stiebel Eltron unit delivers 28.8kW of heating power at 240V. It provides continuous hot water without venting. The design measures 16.6 inches wide and 14.5 inches high. It weighs 19 pounds. You need three dedicated 40-amp breakers and 8-gauge copper wiring. This system suits homes with strong electrical service that need high output for whole-house use.
- 28.8kW heating capacity
- Made in Germany
- Two temperature memory presets
- No venting required
- Requires three separate 40-amp breakers
- Needs 8-gauge copper wiring
- Minimum 200-amp total service
- You have a 200-amp electrical panel
- You need high output for multiple fixtures
- You want a compact unit without venting
- You cannot install three dedicated 40-amp breakers
- You lack space for 8-gauge wiring
- Your panel has less than 200-amp service
Verdict: Stiebel Eltron Tempra 29 Plus 28.8kW fits homes with robust electrical infrastructure. It delivers reliable hot water for whole-house needs. You get German engineering in a space-saving design. This unit is ideal if you can handle the wiring requirements.
Ranein 4.3 GPM Indoor Propane Tankless Water Heater
Best for: Whole-home propane heating for 3-4 fixtures
- Features
- Tankless
- Fuel Type
- Propane
- Max Flow Rate
- 4.3 GPM
- Heating Capacity
- 100,000 BTU
- Installation Location
- Indoor
- Fixture Capacity
- 3-4 water points
The Ranein propane tankless water heater delivers 4.3 GPM at 100,000 BTU. It supports 3-4 water points simultaneously. The unit features an oxygen-free copper heat exchanger for efficient heating. You get precise temperature control from 95°F to 155°F. Four preset modes simplify seasonal adjustments. This indoor model includes a vent pipe for straightforward installation. It suits homes needing reliable hot water for multiple fixtures.
- 100,000 BTU heating capacity for strong performance
- 4.3 GPM flow rate supports 3-4 water points
- Oxygen-free copper heat exchanger enhances durability
- Four intelligent preset modes for easy operation
- Anti-freeze protection down to 14°F
- 4.3 GPM flow rate is lower than the 11.1 GPM and 4.8 GPM options on this list
- Indoor installation only, unlike outdoor models available from other brands
- Fixed temperature range of 95°F to 155°F limits high-heat customization
- You need hot water for 3-4 simultaneous fixtures
- You prefer propane fuel for your home
- You want a unit with included venting hardware
- You require an outdoor installation model
- You need a flow rate exceeding 4.3 GPM
- You live at an elevation above 2,000 feet
Verdict: Ranein Propane 4.3 GPM Tankless Heater offers solid mid-range performance for whole-home use. It fits households with propane access that need reliable heat for multiple bathrooms and kitchens.
Rinnai 11.1 GPM Condensing Dual-Fuel Water Heater
Best for: large households needing high flow rates
- Features
- Tankless
- Fuel Type
- Natural Gas, Propane
- Max Flow Rate
- 11.1 GPM
- Heating Capacity
- 199k BTU
- Installation Location
- Indoor, Outdoor
- Fixture Capacity
- 7 fixtures
The Rinnai RX199iN delivers up to 11.1 GPM with 199k BTU of heating capacity. It runs on natural gas or propane and fits indoor or outdoor spaces. You get a high energy efficiency factor of .98 and support for seven fixtures. This unit is compact at 55 pounds but requires professional installation for proper setup.
- 11.1 GPM flow rate supports seven fixtures
- 199k BTU heating capacity
- .98 energy efficiency factor
- Dual fuel compatibility with propane or natural gas
- Versa Vent allows indoor or outdoor installation
- Requires professional installation
- WiFi Controlr module is not included
- Labor warranty drops to one year if registration is not completed within 90 days
- You need hot water for seven fixtures simultaneously
- You want high energy efficiency for gas heating
- You have the space for indoor or outdoor mounting
- You prefer electric tankless units
- You plan to install the unit yourself without a technician
- You want built-in WiFi control without buying extra parts
Verdict: Rinnai 11.1 GPM Smart Sense Gas Heater is ideal for large households needing high flow rates and versatile installation options. You should buy this if you prioritize efficiency and capacity over plug-and-play simplicity.
Orbek 14kW 240V Tankless Water Heater
Best for: single sink or shower applications
- Features
- Tankless
- Fuel Type
- Electric
- Max Flow Rate
- 3.38 GPM
- Heating Capacity
- 14kW
- Voltage
- 240V
- Fixture Capacity
- 2-3 points of use
The Orbek 14kW unit delivers up to 3.38 GPM of hot water for two to three points of use. It operates on 240V power and heats water in three seconds. The device features an LED display for temperature control between 86°F and 140°F. Its compact size fits tight corners. This heater suits small households or specific sink and shower applications where high flow is not required.
- Heats water in 3 seconds
- Compact dimensions of 14.2 inches high
- ETL certified for safety
- LED display with precise temperature control
- Lower 14kW heating capacity than most competitors
- Lower 3.38 GPM flow rate limit
- Requires a 60-amp breaker and 6 AWG wires
- You need a heater for one sink or shower
- You have limited electrical panel space for a 60-amp breaker
- You want a compact unit for tight installation spots
- You need to run multiple showers simultaneously
- Your electrical panel cannot support a 60-amp two-pole breaker
- You require a flow rate above 3.38 GPM
Verdict: Orbek 14kW Electric Tankless Heater provides reliable instant heat for single-fixture use. It fits well in homes with limited electrical capacity or tight installation spaces.
WINTEMP 36kW Electric Tankless Water Heater
Best for: Whole-house hot water with high flow needs
- Features
- Tankless
- Fuel Type
- Electric
- Max Flow Rate
- Up to 8.7 GPM
- Heating Capacity
- 36kW
- Voltage
- 240V
- Installation Type
- Whole House
The WINTEMP WN36 is a 36kW electric tankless water heater designed for whole-house use. It delivers a maximum flow rate of 8.7 GPM at 240V. This unit supports up to 3–5 bathrooms in mild climates. You can control the temperature via WiFi. The compact design measures 13.7 inches wide and 21.1 inches high. It requires four 40A circuit breakers for installation.
- High 36kW heating capacity for whole-house use
- Generous 8.7 GPM maximum flow rate
- Built-in WiFi for remote temperature control
- ETL certified for safety and reliability
- Requires four 40A circuit breakers, which is more than most competitors
- Heavier build at 36.1 pounds compared to lighter units
- Limited to 2-year replacement warranty
- You have a 300A electrical service and can install four 40A breakers
- You need hot water for 3–5 bathrooms in a mild climate
- You want WiFi control for your water heater
- You have a standard 100A or 200A electrical panel
- You live in a cold climate with low incoming water temperature
- You prefer a unit with a longer warranty period
Verdict: WINTEMP 36kW Electric Tankless Water Heater fits homes with robust electrical infrastructure that need high flow for multiple bathrooms. It suits users who value WiFi control and do not mind the higher electrical requirements.
APUS 95,000 BTU 4.42 GPM Indoor Propane Heater
Best for: Indoor propane heating for 2–3 fixtures
- Features
- Tankless
- Fuel Type
- Propane
- Max Flow Rate
- 4.42 GPM
- Heating Capacity
- 95,000 BTU
- Installation Location
- Indoor
- Voltage
- 120V
The APUS Propane Tankless Water Heater delivers 95,000 BTU of heating power with a maximum flow rate of 4.42 GPM. It supports 2–3 fixtures simultaneously, making it suitable for whole-house use. The unit features an LED touchscreen and operates quietly at 36dB. It maintains temperature within ±1°F and includes built-in freeze protection for indoor installation.
- 95,000 BTU heating capacity
- 4.42 GPM maximum flow rate
- Temperature control within ±1°F
- Quiet 36dB operation
- Built-in freeze protection
- Lower heating capacity than the 110,000 BTU Rinnai model
- Lower flow rate than the 11.1 GPM Rinnai model
- Shorter warranty than the 12-year Rinnai model
- You need hot water for 2–3 fixtures
- You prefer propane fuel for indoor use
- You want precise temperature stability
- You require a flow rate above 4.42 GPM
- You need a warranty longer than 2 years
- You are looking for a natural gas model
Verdict: APUS Propane 95k BTU Tankless Heater fits households needing steady hot water for multiple fixtures without the bulk of a tank. It is a practical choice for users prioritizing temperature precision and quiet operation over maximum flow capacity.
WINTEMP 11kW 240V Electric Tankless Water Heater
Best for: single sink or small shower point-of-use
- Features
- Tankless
- Fuel Type
- Electric
- Max Flow Rate
- 2.6 GPM
- Heating Capacity
- 11kW
- Voltage
- 240V
- Fixture Capacity
- 1 Shower&Sink
The WINTEMP 11kW electric tankless water heater delivers up to 2.6 GPM at 240V. Its compact 9.7 x 14 x 3.4 inch design saves space for point-of-use applications. The unit features a digital display adjusting from 86°F to 140°F and self-modulating technology for stable temperature control. It is ETL certified and includes overheat and dry-fire protection. This model suits small spaces where high flow is not required.
- 11kW heating capacity for efficient on-demand hot water
- Compact dimensions of 9.7 inches wide and 14 inches high
- Digital temperature control ranging from 86°F to 140°F
- ETL certified with leakage and overheat protection systems
- Lower 2.6 GPM max flow rate compared to higher-capacity models on the list
- Smaller 11kW heating power limits simultaneous fixture use
- Heavier 8.6-pound build relative to its compact size
- You need a compact unit for a single sink or small shower
- You require ETL certification for safe installation
- You want digital temperature control with a wide range
- You need to supply hot water to multiple fixtures simultaneously
- You require a flow rate higher than 2.6 GPM
- You prefer a higher heating capacity for whole-house use
Verdict: WINTEMP 11kW Compact Electric Heater provides reliable point-of-use hot water for tight spaces. It fits buyers who prioritize compact dimensions and stable temperature control over high flow rates.
ThermoMate 4 GPM Propane Tankless Water Heater
Best for: Bathroom single fixture use
- Features
- Tankless
- Fuel Type
- Propane
- Max Flow Rate
- Up to 4 GPM
- Heating Capacity
- 98,500 BTU
- Installation Location
- Indoor
- Voltage
- 120V
This propane tankless water heater delivers up to 4 GPM with 98,500 BTU of heating power. It features a 98% thermal efficiency rating and precise temperature control within ±1°F. The unit includes a 3.5-inch LED display and comprehensive safety protections. Its compact indoor design suits bathroom installations where space is limited. You get stable hot water flow for single fixture use.
- 98% thermal efficiency reduces energy waste
- Precise temperature stability within ±1°F
- Compact indoor dimensions save space
- Comprehensive safety protection features
- Lower flow rate than whole-house competitors
- Propane fuel requires specific venting
- Indoor-only installation constraint
- You need hot water for a single bathroom fixture
- You have limited space for installation
- You want precise temperature control
- You require high flow for multiple fixtures
- You prefer natural gas over propane
- You need outdoor installation capability
Verdict: ThermoMate 98,500 BTU Propane Tankless Heater fits bathroom users who prioritize compact size and precise temperature stability over high flow capacity.
APUS 18kW 4.4 GPM Tankless Water Heater
Best for: Whole-house hot water for 2-3 fixtures
- Features
- Tankless, LED Display
- Fuel Type
- Electric
- Max Flow Rate
- Up to 4.4 GPM
- Heating Capacity
- 18kW
- Installation Location
- Indoor
- Voltage
- 240V
The APUS 18kW electric tankless water heater delivers up to 4.4 GPM at 240V. Its slim 13.7 by 11.4 by 3.54-inch design mounts easily on walls. You get precise digital control with an LED display and a temperature range of 86 to 131°F. This unit suits whole-house needs for two to three simultaneous fixtures while saving floor space.
- Provides up to 4.4 GPM flow rate for multiple fixtures
- Ultra-slim 3.54-inch depth saves installation space
- LED display allows 1°F temperature adjustments from 86°F to 131°F
- Self-modulating technology adjusts power based on flow rate
- 18kW heating capacity is lower than the 24kW and 36kW units on this list
- Requires two 40A breakers and 8 AWG wire for installation
- Indoor-only installation limits outdoor placement options
- You need a compact unit for a small household or apartment
- You want precise digital temperature control with an LED display
- You have the electrical capacity for two 40A breakers
- You require outdoor installation capabilities
- You need a higher flow rate than 4.4 GPM
- You cannot install two dedicated 40A circuits
Verdict: APUS 18kW Electric Tankless Water Heater fits homes needing reliable whole-house hot water for two to three fixtures without taking up floor space. It suits users who value precise temperature control and have the necessary electrical infrastructure.
Ranein 18kW 4.3 GPM Electric Water Heater
Best for: Whole-house electric hot water with precise temp control
- Features
- Tankless
- Fuel Type
- Electric
- Max Flow Rate
- 4.3 GPM
- Heating Capacity
- 18 kW
- Voltage
- 240 V
- Fixture Capacity
- 2–3 household water outlets
The Ranein 18kW delivers up to 4.3 GPM of hot water for whole-house use. It runs on 240V power and supports two to three outlets simultaneously. You get precise temperature control from 86°F to 131°F in 1°F increments. The compact unit measures 13.8 by 18.7 inches and weighs 17.4 pounds. It offers 99% thermal efficiency for energy savings.
- 18 kW heating capacity supports 2–3 outlets
- Max flow rate of 4.3 GPM
- Precise temperature control in 1°F increments
- 99% thermal efficiency reduces energy use
- Compact 13.8-inch width saves space
- 18 kW output is lower than the 24 kW and 36 kW models on this list
- 4.3 GPM flow rate is lower than the 11.1 GPM gas model
- Requires two dedicated 40 A double-pole breakers
- You need a whole-house electric heater for 2–3 outlets
- You want precise temperature adjustments in 1°F increments
- You have the electrical capacity for two 40 A circuits
- You require a flow rate above 4.3 GPM
- You only have a single electrical circuit available
- You prefer a gas-powered unit with higher flow capacity
Verdict: The Ranein 18kW Electric Tankless Water Heater fits households needing reliable whole-house hot water with precise temperature control. It suits users who can install the required dual 40 A circuits and prioritize energy efficiency over maximum flow speed.
SIVUATEK 14kW 240V Electric Tankless Water Heater
Best for: single sink or shower applications
- Features
- Tankless
- Fuel Type
- Electric
- Heating Capacity
- 14 kW
- Voltage
- 240V
- Fixture Capacity
- 1–2 points
- Temperature Range
- 86°F to 131°F
The SIVUATEK 14kW unit is a compact electric water heater designed for sink and shower use. It delivers instant hot water with 99.8% thermal efficiency. The LED display allows precise temperature control from 86°F to 131°F. It requires a 60-amp circuit breaker. This model suits small households needing hot water for one to two fixtures simultaneously.
- 14kW heating power provides instant hot water
- 99.8% thermal efficiency reduces energy waste
- LED display sets temperature in 1°F increments
- Compact 15.87×11.14×2.87 inch size saves space
- ETL certified for safe operation
- 14kW power is lower than many competitors on the list
- Limited to 1–2 fixture capacity
- Requires a 60-amp circuit breaker
- You need hot water for a single sink or shower
- You want precise temperature control in 1°F steps
- You have a 60-amp circuit available for installation
- You need to supply hot water to multiple bathrooms at once
- Your electrical panel cannot support a 60-amp breaker
- You prefer gas-powered heating over electric
Verdict: The SIVUATEK 14kW Electric Tankless Heater is a practical option for small households with limited electrical capacity. It fits users who need reliable hot water for one or two fixtures without complex installation.
03 Specifications side by side
| Spec | Rheem 18kW 240V Electric Tankless Water Heater | Thermomate 18kW Electric Tankless Water Heater | Westinghouse 24kW WiFi Tankless Water Heater | VancEpic 4.8 GPM Natural Gas Tankless Heater | Stiebel Eltron Tempra 29 Plus 28.8kW Tankless | Ranein 4.3 GPM Indoor Propane Tankless Water Heater | Rinnai 11.1 GPM Condensing Dual-Fuel Water Heater | Orbek 14kW 240V Tankless Water Heater | WINTEMP 36kW Electric Tankless Water Heater | APUS 95,000 BTU 4.42 GPM Indoor Propane Heater | WINTEMP 11kW 240V Electric Tankless Water Heater | ThermoMate 4 GPM Propane Tankless Water Heater | APUS 18kW 4.4 GPM Tankless Water Heater | Ranein 18kW 4.3 GPM Electric Water Heater | SIVUATEK 14kW 240V Electric Tankless Water Heater |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Fuel Type | Electric | Electric | Electric | Natural Gas | Electric | Propane | Natural Gas, Propane | Electric | Electric | Propane | Electric | Propane | Electric | Electric | Electric |
| Max Flow Rate | up to 4.4 GPM | Up to 4.4GMP | 5.55 GPM | 4.8 GPM | – | 4.3 GPM | 11.1 GPM | 3.38 GPM | Up to 8.7 GPM | 4.42 GPM | 2.6 GPM | Up to 4 GPM | Up to 4.4 GPM | 4.3 GPM | – |
| Heating Capacity | 18kW | 18kW | 24 kW | 110,000 BTU | 28.8kW | 100,000 BTU | 199k BTU | 14kW | 36kW | 95,000 BTU | 11kW | 98,500 BTU | 18kW | 18 kW | 14 kW |
| Installation Location | – | Indoor | – | Indoor | – | Indoor | Indoor, Outdoor | – | – | Indoor | – | Indoor | Indoor | – | – |
| Voltage | 240V | 240 Volt | 240 V | – | 240 or 208-volt | – | – | 240V | 240V | 120V | 240V | 120V | 240V | 240 V | 240V |
| Fixture Capacity | – | – | Shower and sink | 3-5 water outlets | – | 3-4 water points | 7 fixtures | 2-3 points of use | – | 2–3 Fixtures | 1 Shower&Sink | 1 shower and 1 faucet | 2–3 Points | 2–3 household water outlets | 1–2 points |
| Temperature Range | – | 80°F to 140°F | – | – | – | 95°F-155°F | – | 86°F to 140°F | – | 95–140°F | 86°F–140°F | 90–140°F | 86–131°F | 86°F to 131°F | 86°F to 131°F |
| Installation Type | – | – | Whole House | – | – | – | – | – | Whole House | – | – | – | – | Whole House | – |
| Features | Tankless | Tankless | Tankless | Tankless, Child Safety Lock, LED Display | Tankless | Tankless | Tankless | Tankless | Tankless | Tankless | Tankless | Tankless | Tankless, LED Display | Tankless | Tankless |
| Application | – | Shower | Bathroom | – | – | – | – | – | – | – | Shower | Bathroom | – | – | Shower |
| Form Factor | – | – | – | – | – | – | – | – | – | – | Compact | – | – | – | – |
| Wattage | 18 kW | 18 kW | – | – | – | – | – | 14 kW | – | – | – | – | 18 kW | 18 kW | 14 kW |
| Intended Use | Home | – | Home | – | Home | Home | – | – | – | – | – | – | – | – | – |
| Dimensions | 18.5 × 14.5 × 3.5 inches | 13.1 × 13.1 × 17.1 inches | 13 × 13 × 17.1 inches | 14.4 × 14.4 × 24.6 inches | 4.63 × 16.6 × 14.5 inches | 14.2 × 14.2 × 22.5 inches | 30.1 × 18.5 × 30.1 inches | 9.5 × 9.5 × 14.2 inches | 13.7 × 13.7 × 21.1 inches | 5.9 × 5.9 × 20.6 inches | 9.7 × 9.7 × 14 inches | 13.8 × 13.8 × 21.7 inches | 11.4 × 11.4 × 13.7 inches | 13.8 × 13.8 × 18.7 inches | 12.2 × 12.2 × 17.3 inches |
| Weight | 14.8 pounds | – | 17 pounds | 25.4 pounds | 19 pounds | – | 55 pounds | – | 36.1 pounds | 19.2 pounds | 8.6 pounds | 21.2 pounds | 15.2 pounds | 17.4 pounds | 15.1 pounds |
| Size | Small | 240V/18kW | L-24 | 4.8GPM, 110,000BTU, NG | 29 (kW) | 4.3GPM Indoor | 11.1 GPM | S-14 | 36kW | – | WN-11 | – | – | – | – |
| Color | Gray | Gray | Gray 24 | Non-Condensing | White | LPG | Silver | Pearl | Gray | Propane Gas,4.42GPM,95,000BTU，Space Gray | Gray | Metallic Silver | Gray | Gray | Gray |
| Model | RTEX-18 | ET180 | WET-24K-G | VH11K-W-NG-U01 | 239223 | RANEIN-43GPM-100KBTU | RX199iN | 14kW 2.0 Model | WN36 | AP-AWH-Q13LPG | YQ-WN11K | CZ360LP | AP-ADSK180-H18 | RE18K | TSB-140 |
If you need specs for off-grid outdoor use, compare the best tankless water heaters for camping.
04 How to choose the right one
Match fuel type to utility
Your available utility dictates the category. Electric units like the Rheem 18kW require dedicated 240V circuits and high amperage. Gas and propane models, such as the Rinnai 11.1 GPM, need venting and gas lines. Electric heaters are often smaller and easier to install indoors. Gas units typically offer higher flow rates for whole-house use. Check your home’s existing infrastructure before deciding. You cannot switch fuel types without major renovation. Select the type that matches your current setup to avoid costly upgrades.
Check flow rate needs
Flow rate determines how many fixtures can run simultaneously. Single-sink units like the Orbek 14kW provide low flow, suitable for one bathroom or kitchen sink. Whole-house models like the Rinnai 11.1 GPM deliver high flow for multiple bathrooms. Look at gallons per minute (GPM) for gas units or kilowatt (kW) ratings for electric ones. Higher kW or GPM means more water capacity. If you have a large family, choose a high-capacity unit. Small households can save space and money with lower flow options.
Verify electrical capacity
Electric tankless heaters demand significant electrical power. The WINTEMP 36kW unit requires robust electrical service to handle its high wattage. Lower power models like the WINTEMP 11kW are better for limited circuits. Ensure your home’s panel can support the required amperage. Overloading circuits causes tripping or damage. Electric units often have compact footprints but high energy demands. Gas units bypass electrical limits but need gas lines. Check your electrical panel’s capacity before buying an electric model to ensure safe operation.
Measure installation space
Physical dimensions determine where the unit fits. The Rheem 18kW is only 3.5 inches high, fitting tight spaces like closets. The Rinnai 11.1 GPM is much larger, requiring more wall space. Measure your installation area before purchasing. Indoor units need ventilation clearance. Outdoor models like the Rinnai must withstand weather. Compact units save space but may have lower flow. Larger units offer more capacity but need more room. Always check width, height, and length specs. Ensure the unit fits your planned location without obstruction.
Consider smart features
Some units offer WiFi control for remote monitoring. The Westinghouse 24kW model includes smart features for convenience. These allow you to adjust settings via an app. Not all units have this capability. Basic models rely on manual controls or LED displays. Smart features add cost and complexity. Decide if remote access is necessary for your lifestyle. For simple hot water needs, basic units suffice. If you want to monitor usage remotely, choose a smart-enabled model. Verify compatibility with your home network before purchasing.
05 Frequently asked questions
What is the difference between electric and gas tankless water heaters?
Electric models like the Rheem 18kW use 240V circuits and wattage to heat water instantly. Gas units like the Rinnai 11.1 GPM use natural gas or propane for higher flow rates. Electric heaters often have smaller footprints, while gas models typically support more simultaneous fixtures.
How many fixtures can a whole-house tankless heater run at once?
Capacity depends on the flow rate. The Rinnai 11.1 GPM supports large households with high flow needs. Smaller whole-house units like the Ranein 4.3 GPM handle three to four fixtures. Check the gallons per minute rating to ensure it matches your household usage.
Do I need a special electrical circuit for an electric tankless heater?
Yes, electric units require dedicated 240V circuits. High-wattage models like the WINTEMP 36kW need robust electrical infrastructure. Lower power options like the Orbek 14kW suit homes with limited capacity. Verify your home’s amperage before installing to avoid tripping breakers.
Which tankless water heater is best for tight spaces?
The Rheem 18kW is ideal for small homes needing compact electric heating. Its 14.5-inch width and 3.5-inch height fit tight spaces. The WINTEMP 11kW is also compact at 9.7 inches wide. These models prioritize space-saving design over maximum flow rate.
Can I use a tankless water heater for a single sink?
Yes, point-of-use units are designed for single fixtures. The Orbek 14kW provides reliable instant heat for one sink or shower. The WINTEMP 11kW offers stable temperature control for small applications. These heaters save space and energy for localized hot water needs.
What fuel types are available for tankless water heaters?
You can choose electric, natural gas, or propane. Electric models include the Rheem 18kW and Westinghouse 24kW. Gas options like the Rinnai 11.1 GPM use natural gas. Propane models like the Ranein 4.3 GPM suit homes with propane access. Select based on your utility availability.
Are smart features available on tankless water heaters?
Some models offer WiFi control for remote monitoring. The Westinghouse 24kW includes smart convenience features. The WINTEMP 36kW also supports WiFi control. These features allow you to manage settings from your phone. Check the product attributes to confirm connectivity options.
