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Choosing the best tankless water heaters for home requires matching your electrical panel and flow needs to the right unit. We compared 8 models based strictly on published specifications. The Rheem 18kW 240V Electric Tankless Water Heater leads because its 18 kW output balances compact size with reliable whole-home performance. This guide helps you decide which heater fits your household’s hot water demands, whether you need precise temperature control, smart features, or specific fuel types like propane or natural gas.
01 Match wattage to your electrical panel
Tankless units range from 13 kW to 28.8 kW. High-power models like the Stiebel Eltron Tempra 29 Plus require robust electrical infrastructure, while smaller units like the NOVIEEX 13kW suit single-bathroom homes. Check your panel capacity before buying. Mismatched power leads to tripped breakers. Select a unit that fits your home’s electrical limits and hot water flow needs.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | Rheem 18kW 240V Electric Tankless Water Heater Best overall | Whole-home hot water with precise control | |
| 2 | Westinghouse 24kW WiFi Tankless Water Heater Also great | Whole-house hot water with smart remote control | |
| 3 | Stiebel Eltron Tempra 29 Plus 28.8kW Tankless Best premium | homes with 200-amp electrical panels | |
| 4 | Ranein 4.3 GPM Indoor Propane Tankless Water Heater Best budget | Indoor propane homes needing 3-4 point support | |
| 5 | Orbek 18kW 240V Tankless Electric Water Heater Best point of use | small bathrooms and single fixtures | |
| 6 | MIZUDO 8.1 GPM Outdoor Natural Gas Tankless Heater Best natural gas | outdoor whole-home hot water | |
| 7 | NOVIEEX 13kW Electric Tankless Heater Best led display | single-bathroom homes needing precise temp control | |
| 8 | APUS 140,000 BTU Indoor Propane Tankless Water Heater Also great | Whole-home propane heating with high flow needs |
02 The best fit for you
- You want whole-home hot water with precise temperature control – Rheem 18kW 240V Electric Tankless Water Heater – The 18 kW electric heating element provides reliable performance for moderate flow needs.
- You need smart remote control for your water heater – Westinghouse 24kW WiFi Tankless Water Heater – Built-in WiFi allows you to monitor and adjust settings from your phone.
- You have a 200-amp electrical panel and need high capacity – Stiebel Eltron Tempra 29 Plus 28.8kW Tankless – The 28.8 kW power output suits homes with robust electrical infrastructure.
- You need a compact unit for a small bathroom – Orbek 18kW 240V Tankless Electric Water Heater – Its compact form factor measures just 8 inches wide and fits tight spaces.
- You want outdoor whole-home hot water from natural gas – MIZUDO 8.1 GPM Outdoor Natural Gas Tankless Heater – This outdoor natural gas heater delivers 8.1 GPM for busy households.
Rheem 18kW 240V Electric Tankless Water Heater
Best for: Whole-home hot water with precise control
- Intended Use
- Home
- Fuel Type
- Electric
- Max Flow Rate
- up to 4.4 GPM
- Heating Capacity
- 18kW
- Voltage
- 240V
- Features
- Tankless
This Rheem electric tankless water heater delivers up to 4.4 GPM at 18 kW. It features external digital thermostatic control with LED display for precise temperature adjustment. The unit uses durable copper immersion heating elements that are field serviceable. Its compact design measures 14.5 by 18.5 by 3.5 inches and weighs 14.8 pounds. It suits homes needing efficient whole-house hot water with simple installation via bottom water connections.
- Up to 4.4 GPM flow rate
- 18 kW heating capacity
- External digital thermostatic control with LED display
- Field serviceable copper immersion heating elements
- Compact dimensions of 14.5 by 18.5 by 3.5 inches
- 18 kW power is lower than the 24 kW and 29 kW options on the list
- 4.4 GPM flow rate is lower than the 6.8 GPM and 8.1 GPM gas models
- Electric fuel type requires 240V electrical infrastructure unlike gas alternatives
- You need a compact electric unit for whole-house hot water
- You want precise temperature control with digital display
- You prefer field serviceable copper heating elements
- You require higher flow rates than 4.4 GPM
- You do not have 240V electrical capacity
- You prefer gas fuel for higher power output
Verdict: Rheem 18kW Electric Tankless Heater offers reliable performance for homes needing moderate hot water flow. It fits households prioritizing compact size and precise temperature control over maximum capacity.
Westinghouse 24kW WiFi Tankless Water Heater
Best for: Whole-house hot water with smart remote control
- Intended Use
- Home
- 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 24kW of heating power for whole-house hot water. It supports up to 5.55 GPM, allowing simultaneous use of a shower and sink. The 240V electric design fits standard residential circuits. You get smart Wi-Fi control and a compact 17.1-inch height. It suits homes needing reliable, on-demand hot water with remote monitoring capabilities.
- 24kW heating capacity provides strong hot water output
- Max flow rate of 5.55 GPM supports shower and sink use
- Smart Wi-Fi enables remote temperature adjustment and monitoring
- Compact dimensions of 17.1 inches high and 13 inches wide
- Lower maximum flow rate than gas models offering 6.8 to 8.1 GPM
- Requires a substantial 100A electrical circuit for operation
- Heavier at 17 pounds compared to lighter plastic units
- You need simultaneous hot water for a shower and a sink
- You want remote temperature control via a smartphone app
- You have a 240V electrical system with a 100A breaker available
- You require a flow rate above 5.55 GPM for multiple bathrooms
- You only have standard 120V outlets and cannot install a 240V circuit
- You prefer gas fuel for higher flow rates and lower electrical load
Verdict: Westinghouse 24kW Electric Tankless Water Heater fits homes needing reliable whole-house hot water with smart features. It suits users who can support the 100A electrical requirement and value remote control over maximum flow speed.
Stiebel Eltron Tempra 29 Plus 28.8kW Tankless
Best for: homes with 200-amp electrical panels
- Intended Use
- Home
- Fuel Type
- Electric
- Heating Capacity
- 28.8kW
- Voltage
- 240 or 208-volt
- Features
- Tankless
- Dimensions
- 4.63 × 16.6 × 14.5 inches
The Stiebel Eltron Tempra 29 Plus is a 28.8kW electric tankless water heater designed for whole-home use. It operates on 240V or 208V power and requires three dedicated 40-amp breakers. The unit measures 16.6 by 14.5 inches and weighs 19 pounds. You get two temperature memory presets for easy adjustment. This model suits households with high electrical capacity seeking reliable, continuous hot water.
- 28.8kW heating capacity for strong output
- Two temperature memory presets for personalized settings
- Compact dimensions at 16.6 by 14.5 inches
- Made in Germany build quality
- Requires three separate 40-amp breakers
- 28.8kW power is lower than gas competitors
- Minimum 200-amp service required
- You have a 200-amp electrical panel
- You need dedicated 40-amp breakers
- You want two temperature presets
- You lack three 40-amp breakers
- You have less than 200-amp service
- You prefer gas fuel types
Verdict: Stiebel Eltron Tempra 29 Plus 28.8kW fits homes with robust electrical infrastructure. It delivers steady hot water for users who can support the high amperage demands.
Ranein 4.3 GPM Indoor Propane Tankless Water Heater
Best for: Indoor propane homes needing 3-4 point support
- Intended Use
- Home
- Fuel Type
- Propane
- Max Flow Rate
- 4.3 GPM
- Heating Capacity
- 100,000 BTU
- Installation Location
- Indoor
- Fixture Capacity
- 3-4 water points
This indoor propane unit delivers 100,000 BTU and up to 4.3 GPM. It supports 3-4 water points simultaneously. The adjustable range is 95°F to 155°F. You get four preset modes for different needs. The copper heat exchanger resists corrosion. It includes an anti-freeze device for cold climates. This heater suits homes needing reliable on-demand hot water.
- 100,000 BTU heating capacity
- 4.3 GPM maximum flow rate
- Supports 3-4 water points
- Oxygen-free copper heat exchanger
- Anti-freeze protection down to 14°F
- 100,000 BTU is lower than the 140,000 BTU and 180,000 BTU options on this list
- 4.3 GPM flow rate is lower than the 6.8 GPM and 8.1 GPM alternatives
- Indoor installation only, unlike outdoor models available in this category
- You need hot water for 3-4 fixtures at once
- You have an existing propane supply
- You want anti-freeze protection for cold weather
- You require more than 4.3 GPM flow
- You need an outdoor unit
- You prefer natural gas over propane
Verdict: Ranein Propane 100k BTU 4.3 GPM fits households that need moderate flow for multiple points without high power demands.
Orbek 18kW 240V Tankless Electric Water Heater
Best for: small bathrooms and single fixtures
- Intended Use
- Home
- Fuel Type
- Electric
- Max Flow Rate
- 4.22 GPM
- Heating Capacity
- 18 kW
- Voltage
- 240 V
- Fixture Capacity
- 2-3 Point of Use
The Oberk 18kW unit delivers 4.22 GPM at 240V, targeting point-of-use or small whole-house needs. Its 18 kW heating capacity supports 2-3 fixtures. The compact 11-inch height and 8-inch width fit tight spaces. It heats water in 3 seconds. ETL certification ensures safety. This model suits buyers needing reliable, instant hot water for limited fixture counts without complex venting.
- 18 kW heating capacity for 4.22 GPM flow
- Compact 11-inch height and 8-inch width
- 3-second instant hot water delivery
- ETL certified with overheat protection
- Lower 18 kW power compared to competitors' 24-29 kW
- Lower 4.22 GPM flow rate than higher-capacity models
- Limited to 2-3 fixture capacity
- You need hot water for a single bathroom or kitchen sink
- You have limited space for a compact wall-mounted unit
- You want ETL-certified electric safety features
- You need to supply hot water to multiple bathrooms simultaneously
- You require a flow rate above 4.22 GPM
- You prefer gas-powered heating options
Verdict: The Oberk 18kW Electric Tankless Heater fits small households needing reliable point-of-use hot water. It is best for tight spaces where lower flow rates are acceptable.
MIZUDO 8.1 GPM Outdoor Natural Gas Tankless Heater
Best for: outdoor whole-home hot water
- Intended Use
- Home
- Fuel Type
- Natural Gas
- Max Flow Rate
- 8.1 GPM
- Heating Capacity
- 180,000 BTU
- Installation Location
- Outdoor
- Voltage
- 120V
This MIZUDO unit delivers 8.1 GPM using 180,000 BTU of natural gas power. It supports 3–5 outlets simultaneously, making it suitable for whole-home use. The device features precise temperature control within ±1°F and activates at a low flow of 0.53 GPM. Designed for outdoor installation, it includes a large LED display and remote panel for easy adjustment.
- 180,000 BTU heating capacity
- 8.1 GPM maximum flow rate
- Supports 3–5 fixtures
- Outdoor-rated design
- ±1°F temperature precision
- Limited to outdoor installation only
- Not recommended above 2,000 feet elevation
- Requires professional installation
- You need high flow for multiple bathrooms
- You have an outdoor wall space for mounting
- You want precise temperature stability
- You require indoor installation
- You live above 2,000 feet elevation
- You cannot hire a professional installer
Verdict: MIZUDO 180k BTU Natural Gas Heater provides high-volume hot water for busy homes with outdoor access. It fits households needing simultaneous hot water for multiple fixtures without indoor space constraints.
NOVIEEX 13kW Electric Tankless Heater
Best for: single-bathroom homes needing precise temp control
- Intended Use
- Home
- Fuel Type
- Electric
- Max Flow Rate
- 3.6 GPM
- Heating Capacity
- 13kW
- Voltage
- 240V
- Fixture Capacity
- 1-2 simultaneous water needs
The NOVIEEX 13kW tankless water heater delivers up to 3.6 GPM of hot water at 240V. It features a slim wall-mounted design and an LED display for precise temperature control from 77°F to 140°F. This unit suits single-bathroom homes or tiny houses needing 1-2 simultaneous water connections. Its 99.8% efficiency eliminates standby heat loss. You get instant hot water with stable flow rates for daily tasks.
- LED digital display allows 1°F precise temperature adjustments
- High 99.8% heating efficiency reduces standby energy loss
- Compact wall-mounted design saves significant space
- 8-layer safety system includes dry-combustion prevention
- 13kW heating capacity is lower than many competitors on the list
- 3.6 GPM flow rate is less than higher-capacity models
- Requires a 60A double-pole circuit breaker for operation
- You need hot water for a single bathroom setup
- You want precise temperature control via an LED display
- You have limited space for a wall-mounted unit
- You require high flow rates for multiple bathrooms
- You cannot install a 60A electrical circuit
- You need a unit for whole-house simultaneous use
Verdict: NOVIEEX 13kW Electric Tankless Heater fits single-bathroom homes where space is tight and precise temperature control matters. It delivers steady hot water for one or two fixtures without the bulk of a traditional tank.
APUS 140,000 BTU Indoor Propane Tankless Water Heater
Best for: Whole-home propane heating with high flow needs
- Intended Use
- Home
- Fuel Type
- Propane
- Max Flow Rate
- Up to 6.8 GPM
- Heating Capacity
- 140,000 BTU
- Installation Location
- Indoor
- Voltage
- 120V AC
The APUS propane tankless water heater delivers up to 6.8 GPM using a 140,000 BTU burner. Its built-in smart booster pump increases flow, while zero-cold water technology minimizes wait times. This indoor unit supports 4–5 water points and maintains temperature within ±1°F. It suits whole-home needs where high flow and precise heating are priorities.
- 140,000 BTU heating capacity for strong performance
- Built-in smart booster pump increases flow up to 130%
- Zero-cold water technology reduces wait time for hot water
- Precise ±1°F temperature control via LED display or app
- Lower heating capacity than the 180,000 BTU option on this list
- Indoor installation only, unlike the outdoor-capable model also listed
- You need high flow rates for 4–5 simultaneous water points
- You want precise temperature stability across different seasons
- You prefer propane fuel for whole-home heating
- You require outdoor installation capabilities
- You need the highest available heating capacity on this list
- You prefer electric heating over propane fuel sources
Verdict: APUS Propane Tankless Water Heater 140k BTU fits homes needing reliable high-flow hot water for multiple fixtures. Its booster pump and precise controls make it a solid choice for whole-house propane setups.
03 Specifications side by side
| Spec | Rheem 18kW 240V Electric Tankless Water Heater | Westinghouse 24kW WiFi Tankless Water Heater | Stiebel Eltron Tempra 29 Plus 28.8kW Tankless | Ranein 4.3 GPM Indoor Propane Tankless Water Heater | Orbek 18kW 240V Tankless Electric Water Heater | MIZUDO 8.1 GPM Outdoor Natural Gas Tankless Heater | NOVIEEX 13kW Electric Tankless Heater | APUS 140,000 BTU Indoor Propane Tankless Water Heater |
|---|---|---|---|---|---|---|---|---|
| Fuel Type | Electric | Electric | Electric | Propane | Electric | Natural Gas | Electric | Propane |
| Max Flow Rate | up to 4.4 GPM | 5.55 GPM | – | 4.3 GPM | 4.22 GPM | 8.1 GPM | 3.6 GPM | Up to 6.8 GPM |
| Heating Capacity | 18kW | 24 kW | 28.8kW | 100,000 BTU | 18 kW | 180,000 BTU | 13kW | 140,000 BTU |
| Installation Location | – | – | – | Indoor | – | Outdoor | – | Indoor |
| Voltage | 240V | 240 V | 240 or 208-volt | – | 240 V | 120V | 240V | 120V AC |
| Fixture Capacity | – | Shower and sink | – | 3-4 water points | 2-3 Point of Use | 3-5 Outlets | 1-2 simultaneous water needs | 4–5 Points |
| Temperature Range | – | – | – | 95°F-155°F | – | 95-167°F | 77°F to 140°F | 95–140°F |
| Installation Type | – | Whole House | – | – | Whole House | – | – | – |
| Features | Tankless | Tankless | Tankless | Tankless | Tankless | Tankless | Tankless, LED Display | Tankless |
| Application | – | Bathroom | – | – | Point of Use | – | – | – |
| Form Factor | – | – | – | – | Compact | – | – | – |
| Wattage | 18 kW | – | – | – | 18 kW | – | – | – |
| Intended Use | Home | Home | Home | Home | Home | Home | Home | Home |
| Dimensions | 18.5 × 14.5 × 3.5 inches | 13 × 13 × 17.1 inches | 4.63 × 16.6 × 14.5 inches | 14.2 × 14.2 × 22.5 inches | 8 × 8 × 11 inches | 17.1 × 17.1 × 26.2 inches | 11.1 × 11.1 × 15.9 inches | 7.09 × 7.09 × 21.3 inches |
| Weight | 14.8 pounds | 17 pounds | 19 pounds | – | – | – | – | 26.9 pounds |
| Size | Small | L-24 | 29 (kW) | 4.3GPM Indoor | M-18 | Natural Gas, 8.1 GPM, 180,000 BTU, Indoor | – | – |
| Color | Gray | Gray 24 | White | LPG | Snow | White 8.1NG | Silver | Space Gray |
| Model | RTEX-18 | WET-24K-G | 239223 | RANEIN-43GPM-100KBTU | HEU-ET018A5W-M0 | HS180A0W-NG | DS-18 | AP-AWH-Q20LPG |
If you require lower flow rates for remote properties, review specs for the best tankless water heaters for cabins.
04 How to choose the right tankless water heater
Check electrical panel capacity
Electric tankless heaters draw significant power. The Rheem 18kW model requires a 240V circuit, which is standard for many homes. However, the Stiebel Eltron Tempra 29 Plus draws nearly 30 kW. This high wattage demands a robust 200-amp electrical panel. If your home has an older or smaller panel, a high-kilowatt unit will trip breakers or fail to operate. Always verify your home’s electrical service matches the unit’s voltage and amperage requirements before purchasing. Mismatched power leads to poor performance or installation issues.
Decide on installation location
Your home layout dictates whether you need an indoor or outdoor unit. The MIZUDO 8.1 GPM model is designed for outdoor installation, freeing up interior space. It handles whole-home needs but requires protection from the elements or a covered area. In contrast, the Ranein Propane unit is rated for indoor use. Indoor units often require specific ventilation clearances. Ensure your chosen location meets the manufacturer’s safety codes for gas or electric venting and access. Outdoor units may need additional weatherproofing considerations.
Match flow rate to usage
Flow rate determines how many fixtures can run simultaneously. The MIZUDO unit offers 8.1 GPM, supporting multiple showers and appliances. The Ranein model provides 4.3 GPM, suitable for three to four points. Smaller units like the Orbek 18kW are best for point-of-use applications, such as a single bathroom sink. If you need hot water for a full bath and kitchen at the same time, choose a higher GPM rating. Lower flow rates may result in lukewarm water when multiple taps are open.
Select the correct fuel type
Fuel availability is a primary constraint. Electric models like the Rheem 18kW are common but depend on grid power. Gas units, such as the APUS Propane heater, offer high BTU output (140,000 BTU) for rapid heating. The MIZUDO unit uses natural gas, which is often cheaper to run than propane. Electric units generally have lower upfront costs but higher electricity bills. Gas units require gas line connections and venting. Choose the fuel source you already have or can easily install in your home.
Consider smart features
Remote monitoring adds convenience for many users. The Westinghouse 24kW model includes WiFi connectivity, allowing you to adjust temperatures from your phone. This is useful for managing energy use when you are away. Other models, like the NOVIEEX, feature an LED display for local temperature control. Decide if you need remote access or if local controls suffice. Smart features add complexity but offer greater flexibility. Ensure your home network supports the required connectivity for these units to function correctly.
05 Frequently asked questions
What is the smallest tankless water heater for home use?
The Orbek 18kW Electric Tankless Heater is the most compact option on this list. Its dimensions measure just 8 inches wide and 11 inches high. This small form factor makes it ideal for tight spaces under sinks or in small bathrooms. It is designed specifically for point-of-use applications rather than whole-home supply.
Which tankless water heater works best for outdoor installation?
The MIZUDO 8.1 GPM Outdoor Natural Gas Tankless Heater is built for outdoor use. It delivers high-volume hot water with an 180,000 BTU output. This unit is suitable for busy homes that need simultaneous hot water for multiple fixtures without taking up indoor space. Its robust design handles outdoor environmental conditions effectively.
Do any tankless water heaters have WiFi connectivity?
Yes, the Westinghouse 24kW WiFi Tankless Water Heater includes built-in WiFi. This feature allows you to monitor and adjust settings remotely from your phone. It is a strong choice for users who value smart home integration and remote control capabilities alongside reliable whole-house hot water performance.
What is the highest capacity tankless water heater for home?
The MIZUDO 8.1 GPM Outdoor Natural Gas Tankless Heater offers the highest flow rate at 8.1 gallons per minute. It uses natural gas with an 180,000 BTU output to sustain this high volume. This makes it the best option for households with high simultaneous hot water demands across multiple fixtures.
Which tankless water heater is best for propane fuel?
The Ranein 4.3 GPM Indoor Propane Tankless Water Heater is a top choice for propane users. It provides 100,000 BTU of heat for indoor installation. This model supports three to four fixtures simultaneously, making it suitable for homes that need moderate flow without the high electrical demands of electric units.
What is the most powerful electric tankless water heater?
The Stiebel Eltron Tempra 29 Plus is the most powerful electric model with a 28.8 kW output. It requires a robust electrical infrastructure, specifically a 200-amp panel, to operate safely. This unit delivers steady hot water for homes that can support its high amperage demands and need maximum heating capacity.
