Looking for a tankless water heater? The best models offer continuous hot water, energy savings, and space efficiency. The Rinnai RXP199iN stands out as the best overall for its reliable performance and high flow rate, while the Rheem RTEX-24 offers excellent electric options for smaller budgets. However, choosing the right tankless heater involves tradeoffs between capacity, fuel type, installation complexity, and upfront costs. Continue reading for a detailed breakdown of the top models and what to consider before buying.
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Key Takeaways
- High flow rate models like Rinnai RXP199iN excel for larger households or simultaneous use.
- Electric tankless heaters are generally more affordable and easier to install but may struggle with high demand.
- Gas-powered units support higher flow rates, making them suitable for bigger homes or commercial use.
- Size and installation requirements vary significantly; proper sizing prevents shortages or energy waste.
- Budget models often compromise on flow rate or build quality, so investing in a reputable brand can pay off long-term.
| tankless water heater | Flow Rate | Power | Voltage |
|---|---|---|---|
| Rheem 11kW Multi Fixture Tankl | up to 2.68 GPM | 11kW | 240V |
| Rinnai RX180iN Condensing Smar | 10 GPM | — | — |
| Rheem RTEX-24 24kW 240V Electr | up to 5.9 GPM | 24kW | 240V |
| Rinnai RXP199iN Condensing Sma | 11.1 GPM | — | — |
| Rinnai RX160iN Condensing Smar | 9 GPM | — | — |
| Rheem RTEX-08 8kW Professional | up to 1.95 GPM | 8kW | 240V |
| 14kW Tankless Electric Water H | 3.38 GPM | 14kW | 240V |
| Rheem 240V Tankless Water Heat | up to 3.17 GPM | 13kW | 240V |
| NOVIEEX 18kW Electric Tankless | 4.9 GPM | 18kW | 240V |
| Rinnai RX199iN Condensing Smar | 11.1 GPM | — | — |
| 12kW Electric Tankless Water H | Up to 2.8 GPM | 12kW | 240V |
| Rheem 18kW 240V Tankless Elect | Up to 4.4 GPM | 18kW | 240V |
More Details on Our Top Picks
Rheem 11kW Multi Fixture Tankless Electric Water Heater – 240V
This Rheem model stands out for its space-saving design while still supporting multiple fixtures, making it ideal for apartments or small homes. Compared to larger electric units like the Rheem RTEX-24, it offers a lower flow rate of 2.68 GPM, which limits its capacity for simultaneous use. Its energy efficiency benefits from heating water only when needed, but professional installation is a must due to its specific electrical requirements, adding to the initial setup complexity. The absence of venting simplifies installation but might restrict placement options. Overall, it suits those with modest hot water needs who prioritize saving space but should be prepared for installation constraints.
Pros:- Compact, space-efficient design
- Energy-saving operation by heating water on demand
- Suitable for multiple fixtures despite small size
Cons:- Requires professional electrical installation
- Flow rate limited to 2.68 GPM, restricting simultaneous use
- Not suitable for high-demand households
Best for: Small households or apartments needing reliable, space-efficient hot water for a few fixtures.
Not ideal for: Large families or homes with high simultaneous hot water demands, as the limited flow rate can quickly become a bottleneck.
- Power:11kW
- Voltage:240V
- Flow Rate:up to 2.68 GPM
- Temperature Range:80°F – 140°F
- Warranty:5-Year Leak, 1-Year Parts
Our verdict“This model is perfect for space-constrained setups with modest hot water needs, but not for large households.”
Rinnai RX180iN Condensing Smart Sense Tankless Water Heater, 10 GPM, 180k BTU, Indoor/Outdoor, Supports Natural Gas or Propane
The Rinnai RX180iN excels for households that need a high flow rate of 10 GPM, making it suitable for larger families or homes with multiple bathrooms. Its compact size and support for both natural gas and propane add versatility, especially compared to larger, less flexible models. The high energy efficiency (UEF 0.98) and smart controls for operation and maintenance give it an edge over simpler units like the Rheem RTEX-24, which lacks smart features. However, professional installation is recommended, and outdoor setups require a vent cap, adding some complexity. This heater makes the most sense for those who want a reliable, continuous supply of hot water with smart tech integration.
Pros:- Supports both natural gas and propane
- High flow rate of 10 GPM for multiple fixtures
- Smart controls and learning algorithms improve efficiency
Cons:- Requires professional installation
- WiFi control sold separately
- Outdoor installation needs a vent cap
Best for: Medium to large households seeking a reliable, efficient, and smart-controlled water heater for indoor or outdoor use.
Not ideal for: Homeowners with limited space or those unwilling to handle professional installation, or who prefer simple, manual systems without smart features.
- Flow Rate:10 GPM
- BTU:180,000
- Gas Type:Natural Gas or Propane
- Installation:Indoor/Outdoor
- Efficiency:UEF 0.98
- Warranty:15-year heat exchanger, 5-year parts and labor
Our verdict“Ideal for larger households demanding high flow rates and smart features, with installation complexity a minor consideration.”
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater
The Rheem RTEX-24 offers a significant step up in power and capacity compared to smaller electric units. Its digital temperature display and self-modulating technology enable precise control and energy efficiency, making it suitable for households with moderate hot water needs. Unlike the Rheem 11kW unit, it can support a flow rate up to 5.9 GPM, better handling multiple fixtures at once. However, its reliance on a 240V power supply and the need for professional installation can be deterrents for some buyers. While it provides continuous hot water, its capacity may still fall short in very large or high-demand homes, requiring careful sizing before purchase.
Pros:- Digital temperature control for accuracy
- Self-modulating power reduces energy waste
- Provides continuous hot water up to 5.9 GPM
Cons:- Requires 240V electrical setup, professional installation needed
- Flow rate may not meet very high demand in large households
Best for: Families or small households needing reliable, adjustable hot water with higher flow capacity than basic electric models.
Not ideal for: Very large households with multiple bathrooms or high simultaneous hot water use, where flow rate might be insufficient.
- Model:RTEX-24
- Power:24kW
- Voltage:240V
- Flow Rate:up to 5.9 GPM
- Water Connections:Bottom 3/4″ NPT
Our verdict“Best suited for medium-sized homes seeking precise, adjustable electric hot water, but not for high-demand large families.”
Rinnai RXP199iN Condensing Smart Sense Tankless Water Heater, 11.1 GPM, Indoor/Outdoor, NG or Propane
The Rinnai RXP199iN is engineered for busy households that need a high flow rate of 11.1 GPM, supporting multiple fixtures simultaneously. Its smart recirculation technology learns usage patterns, which enhances efficiency over time—an advantage over simpler models like the Rinnai RX180iN. Its compact size and support for both natural gas and propane make it flexible for various installation settings. The higher BTU rating and longer warranties further support its role as a premium, high-capacity unit. The need for professional installation and extra venting for outdoor setups are minor tradeoffs for its performance and smart features, making it ideal for those prioritizing continuous, high-volume hot water with smart tech.
Pros:- High flow rate of 11.1 GPM
- Smart recirculation that learns usage patterns
- Supports natural gas or propane
Cons:- Requires professional installation
- WiFi control module sold separately
- Vent cap needed for outdoor installation
Best for: Large households or commercial settings requiring high flow rates and smart recirculation for efficiency.
Not ideal for: Small homes or users preferring simple, manual systems without smart features or advanced tech.
- Flow Rate:11.1 GPM
- BTU:199,000
- Fuel Type:NG or Propane
- Installation Options:Indoor/Outdoor
- Recirculation Technology:Smart-Circ
- Warranty:15-year heat exchanger, 5-year parts, 5-year labor
Our verdict“Designed for demanding households needing continuous hot water with smart efficiency, with installation complexity offset by performance.”
Rinnai RX160iN Condensing Smart Sense Tankless Water Heater, 9 GPM, 160k BTU, Indoor/Outdoor, Supports Natural Gas or Propane
The Rinnai RX160iN balances high efficiency with a moderate flow rate of 9 GPM, making it a fitting choice for smaller households or homes with fewer fixtures. Its support for both natural gas and propane adds flexibility, and its compact form factor allows for installation in tight spaces, including outdoor locations with venting considerations. Compared to the larger RX199iN, it offers slightly less capacity but remains highly efficient with a UEF of 0.97. Its smart controls help optimize operation, yet installation still requires a professional and outdoor setups need vent caps. This unit delivers dependable hot water for moderate needs without the bulk of larger models.
Pros:- Compact size fits in small spaces
- Supports both natural gas and propane
- High energy efficiency with UEF .97
Cons:- Professional installation recommended
- Requires vent cap for outdoor use
- Flow rate may be insufficient for large households
Best for: Small to medium homes seeking efficient, smart-controlled hot water without high capacity requirements.
Not ideal for: Large households or homes with high simultaneous hot water demand, where the 9 GPM flow may fall short.
- Flow Rate:9 GPM
- BTU:160,000
- Gas Type:Natural Gas or Propane
- Installation:Indoor/Outdoor
- Warranty:15-year heat exchanger, 5-year parts and labor
Our verdict“A smart, efficient choice for smaller households needing reliable hot water in a compact form.”
Rheem RTEX-08 8kW Professional Classic 240V Tankless Electric Water Heater
The Rheem RTEX-08 stands out for its compact size and adjustable digital temperature control, making it ideal for small apartments or secondary bathrooms where space is tight. Compared to larger units like the NOVIEEX 18kW, it offers lower flow capacity—up to 1.95 GPM—making it less suitable for high-demand households. Its self-modulating technology improves energy efficiency, but the limited flow rate means it can’t support multiple fixtures simultaneously. Additionally, its requirement for a 240V outlet may restrict installation options in some homes. This heater provides precise control in a small footprint but sacrifices capacity for convenience.
Pros:- Compact design fits in tight spaces
- Adjustable digital temperature display for accuracy
- Self-modulating power for energy savings
- Easy to install in limited areas
Cons:- Limited flow rate restricts use in larger households
- Requires 240V outlet, which may not be available everywhere
Best for: Single fixture or small space applications where compact size and precise control are priorities.
Not ideal for: Large households needing simultaneous multiple hot water outlets or homes lacking 240V wiring.
- Model:RTEX-08
- Power:8kW
- Voltage:240V
- Flow Rate:up to 1.95 GPM
- Water Connections:1/2″ NPT
Our verdict“This model works best for small-scale, space-constrained applications where precise temperature control is more important than high flow capacity.”
14kW Tankless Electric Water Heater, On Demand, 240V, 3.38 GPM, LED Display, ETL Certified
The 14kW unit offers a significant upgrade over smaller models like the Rheem RTEX-08, providing a flow rate of 3.38 GPM suitable for small to medium households. Its precise temperature control—adjustable within 1°F—and energy efficiency can lead to up to 60% savings compared to traditional heaters, making it an appealing choice for eco-conscious users. However, its requirement for a 60A circuit breaker and potentially complex installation make it less suitable for DIYers or homes with limited electrical capacity. Compared with the NOVIEEX 18kW, it supports fewer fixtures but offers easier installation in standard homes. Its compact size makes it ideal for those needing reliable hot water at multiple points without the bulk of larger units.
Pros:- Supports multiple fixtures simultaneously
- Precise temperature control with LED display
- Energy-efficient, saving up to 60%
- Compact and space-saving design
Cons:- Requires a 60A circuit breaker, complicating installation
- Installation may be challenging without professional help
Best for: Families or small households wanting reliable, simultaneous hot water at multiple fixtures with manageable electrical needs.
Not ideal for: Large households with high hot water demand or homes with restricted electrical capacity.
- Power:14kW
- Voltage:240V
- Flow Rate:3.38 GPM
- Temperature Range:86°F – 140°F
- Dimensions:14.2″H x 9.5″L x 3.1″W
Our verdict“Ideal for small to medium households seeking efficient hot water without the complexity of very high power units.”
Rheem 240V Tankless Water Heater RTEX-13
The Rheem RTEX-13 provides a flow rate of up to 3.17 GPM, making it comparable to the 14kW model but with a focus on durability and digital controls. Its LED display allows for easy temperature adjustments, and copper heating elements enhance longevity. Compared to the smaller RTEX-08, it offers more capacity but still may struggle with larger households or simultaneous multiple fixtures. Its energy efficiency at 99.8% and included adapters simplify installation, though it still requires a 240V outlet. This heater balances capacity and ease of use, making it suitable for users wanting reliable performance without going to the higher power levels of larger units like the NOVIEEX 18kW.
Pros:- Digital temperature control with LED display
- Highly energy-efficient at 99.8%
- Durable copper heating elements
- Easy to install with included adapters
Cons:- Flow rate might be insufficient for high-demand scenarios
- Requires 240V power supply, limiting placement options
Best for: Homeowners needing a durable, reliable heater with digital controls for moderate hot water demands.
Not ideal for: Large families or homes with high simultaneous hot water needs, where higher flow rates are necessary.
- Voltage:240V
- Model:RTEX-13
- Flow Rate:up to 3.17 GPM
- Power:13kW
- Energy Efficiency:99.8%
Our verdict“A solid choice for moderate hot water needs with a focus on durability and digital convenience.”
NOVIEEX 18kW Electric Tankless Water Heater, 240V, Instant Hot Water, 4.9 GPM
The NOVIEEX 18kW unit excels in delivering high flow rates—up to 4.9 GPM—making it suitable for larger households or those with multiple simultaneous hot water outlets. Its space-saving wall-mount design maximizes interior space, while its smart controls and high thermal efficiency (99.8%) ensure reliable performance. Compared with smaller models like the Rheem RTEX-08, it handles greater demand but comes with the complexity of high electrical requirements—needing two 40A double-pole breakers—and professional installation. For homes where simultaneous use of multiple fixtures is common, this heater offers a robust solution, though its size and power needs may limit where it can be installed easily.
Pros:- High flow rate supports multiple fixtures
- Space-efficient wall-mount design
- Smart, precise temperature control
- High thermal efficiency at 99.8%
Cons:- Requires professional installation due to electrical demands
- High power consumption and wiring complexity
Best for: Large households or homes with multiple bathrooms needing high hot water flow simultaneously.
Not ideal for: Small apartments or homes with limited electrical infrastructure, due to high power and installation complexity.
- Power:18kW
- Voltage:240V
- Flow Rate:4.9 GPM
- Dimensions:11.14″ x 15.86″ x 3.18″
- Max Current:75A
Our verdict“Best suited for large homes where high hot water demand and simultaneous use are common, despite installation challenges.”
Rinnai RX199iN Condensing Smart Sense Tankless Water Heater, 11.1 GPM, 199k BTU, Indoor/Outdoor, Supports Natural Gas or Propane
The Rinnai RX199iN supports a remarkable 11.1 GPM, making it ideal for large households or small commercial applications. Its condensing technology ensures high energy efficiency with a UEF of 0.98, outperforming many electric models like the Rheem RTEX-13 in terms of fuel savings over time. Its support for both natural gas and propane adds flexibility, and the indoor/outdoor installation options expand placement choices. While professional installation and venting are required, this model offers long-term reliability and capacity that electric units can’t match. Compared with smaller electric heaters, the RX199iN provides the capacity needed for demanding households but involves higher initial costs and maintenance complexity.
Pros:- Supports both natural gas and propane
- High flow rate of 11.1 GPM
- Excellent energy efficiency with UEF 0.98
- Indoor and outdoor installation flexibility
Cons:- Requires professional installation and venting
- Higher upfront cost and maintenance complexity
Best for: Large households or residential buildings seeking high flow rates and fuel flexibility with long-term efficiency.
Not ideal for: Small homes or users with limited ventilation options, due to venting requirements and higher setup costs.
- Flow Rate:11.1 GPM
- BTU:199,000
- Gas Type:Natural Gas or Propane
- Installation:Indoor/Outdoor
- Efficiency:UEF 0.98
- Warranty:15-year heat exchanger, 5-year parts/labor
Our verdict“This unit makes the most sense for large homes demanding high capacity and fuel flexibility despite higher installation requirements.”
12kW Electric Tankless Water Heater 240V WiFi On-Demand, Up to 2.8 GPM, Self-Modulating, ETL Certified
This 12kW electric tankless water heater stands out for its combination of space-saving design and smart features. Unlike larger models like the Rheem 18kW, it is ideal for point-of-use applications such as sinks or small bathrooms, especially where space is tight. Its WiFi connectivity allows for remote temperature adjustments, a feature that adds convenience over traditional models. However, the 2.8 GPM flow rate limits its capacity to support multiple fixtures simultaneously, making it less suitable for busy households. Its self-modulating technology enhances energy efficiency, but the requirement for a dedicated 240V electrical connection can complicate installation in some homes. Overall, this pick is perfect for users needing controlled hot water at a single point, with a premium on space and remote management.
Pros:- Remote WiFi control for easy temperature adjustments
- Compact, space-saving wall-mounted design
- Self-modulating technology for energy savings
- Multiple safety protections including leak and overheat prevention
Cons:- Requires dedicated 240V wiring, which may need electrical upgrades
- Limited flow rate restricts use to single fixtures or low-demand scenarios
- Not suitable for high-flow or multi-bathroom setups
Best for: Small households or individual sinks in homes with limited space that want remote control features
Not ideal for: Large households or simultaneous multi-fixture use, due to its limited flow rate
- Power:12kW
- Voltage:240V
- Flow Rate:Up to 2.8 GPM
- Temperature Range:86°F – 140°F
- Dimensions:12.2″ H x 8.1″ W x 3.6″ D
- Water Connections:1/2″ NPT
- Safety Certifications:ETL
Our verdict“This model makes the most sense for small-scale applications where remote control and space are priorities, but it won’t support multiple fixtures at once.”
Rheem 18kW 240V Tankless Electric Water Heater, Gray
The Rheem 18kW model offers a significant increase in flow capacity compared to the smaller WiFi-enabled unit, supporting up to 4.4 GPM, which makes it suitable for multiple fixtures or larger households. Its digital thermostat with LED display ensures precise temperature control, a feature that surpasses simpler analog controls. Compared to the 12kW WiFi heater, it provides more hot water output but requires a robust 240V power supply, potentially needing electrical upgrades in some homes. The copper heating elements contribute to durability, but the higher power draw means installation can be more complex and costly. This model is ideal for users who need reliable hot water for multiple outlets but are prepared for a more involved setup process.
Pros:- Digital thermostat with LED display for easy, precise control
- High flow rate of up to 4.4 GPM supports multiple fixtures
- Durable copper heating elements for longevity
- Simple threaded water connections for straightforward installation
Cons:- Requires a 240V electrical system, possibly needing upgrades
- Higher power consumption can increase energy costs
- Flow rate may still be insufficient for very large households or high-demand scenarios
Best for: Larger households or small homes with multiple simultaneous hot water demands
Not ideal for: Small apartments or single-use applications, as the higher power and flow rate are unnecessary
- Power:18kW
- Voltage:240V
- Flow Rate:Up to 4.4 GPM
- Heating Elements:Copper immersion, field serviceable
- Color:Gray
- Water Connection:bottom 3/4 inch NPT
Our verdict“This Rheem model is best suited for households with multiple simultaneous hot water needs and existing electrical capacity, but it involves a more complex installation process.”
How We Picked
To determine the best tankless water heaters, I evaluated each model based on performance, reliability, ease of installation, energy efficiency, and user reviews. Capacity and flow rate were prioritized for suitability across different household sizes, while fuel type and compatibility ensured options for various homes. Cost-to-value ratio also played a critical role, balancing initial investment against long-term savings. The ranking reflects a mix of these factors, highlighting models that deliver dependable performance for their intended use cases.Factors to Consider When Choosing Tankless Water Heaters
Choosing the right tankless water heater requires understanding several key factors. Beyond just capacity and fuel type, buyers should consider installation complexity, energy efficiency, and ongoing maintenance. Making an informed choice can prevent costly mistakes like undersized units or incompatible fuel sources. This guide breaks down the most important considerations to help match your household needs with the right model.Capacity and Flow Rate
Capacity determines how much hot water the heater can supply at once. Larger households or homes with multiple bathrooms need models with higher flow rates, often measured in GPM (gallons per minute). Choosing an undersized unit leads to cold showers, while an oversized one wastes energy. Assess your household’s peak water demand to pick a model that balances capacity with efficiency.
Fuel Type and Compatibility
Electric and gas are the main options, each with pros and cons. Electric models are easier to install, with lower upfront costs, but typically support lower flow rates. Gas units support higher flow rates and are better suited for larger homes, but require proper venting and more complex installation. Confirm your home’s existing fuel infrastructure before choosing.
Installation and Space Requirements
Some models are compact enough for tight spaces, while others need dedicated room or external venting. Proper installation can prevent future problems and ensure safety. Consider whether you need indoor or outdoor units, and if your home’s wiring or gas lines can support the chosen model. Professional installation may add to initial costs but ensures safety and compliance.
Energy Efficiency and Operating Costs
Look for models with high energy factor ratings and features like self-modulation, which adjusts power consumption based on demand. While premium units may cost more initially, they often save money over time through lower utility bills. Balance upfront costs with long-term savings when selecting a model.
Budget and Long-term Value
Lower-cost models can be tempting but often sacrifice durability or performance. Investing in a well-reviewed, reputable brand tends to provide better reliability and fewer maintenance issues. Consider the total cost of ownership, including energy savings and potential repair costs, before making your decision.
Frequently Asked Questions
Can a tankless water heater supply enough hot water for my entire household?
It depends on the flow rate and capacity of the specific model you choose. Larger households with multiple bathrooms often require units with higher GPM ratings, such as 8-11 GPM. Proper sizing based on your peak water demand ensures everyone has hot water when needed. Consulting a professional for sizing helps prevent shortages and ensures optimal performance.
Is electric or gas better for a tankless water heater?
Electric models are generally easier and cheaper to install, making them suitable for smaller homes or supplemental heating. Gas units support higher flow rates, making them better for larger households or homes with higher hot water demand. The choice also depends on your home’s existing fuel infrastructure and local energy costs.
How much does installation typically cost?
Installation costs vary significantly depending on fuel type, unit size, and existing infrastructure. Electric units usually cost less to install, often between $500 and $1,500, while gas models may range from $1,500 to over $3,000 due to venting and safety requirements. Professional installation ensures safety, compliance, and optimal performance, which can save money long-term.
Are electric tankless water heaters energy-efficient?
Yes, electric models tend to be highly efficient because they convert almost all of the electrical energy into heat. However, their capacity is often limited, which can affect suitability for larger households. Energy efficiency also depends on proper sizing and installation, so selecting a unit with self-modulating technology can further reduce power consumption.
What maintenance do tankless water heaters require?
Most models require minimal maintenance, typically including flushing the system annually to prevent mineral buildup, especially in hard water areas. Regular inspections of venting and filters can extend the lifespan of gas units. Following manufacturer guidelines helps maintain efficiency and avoid costly repairs, ensuring your system runs smoothly for years.
Conclusion
For households seeking the best overall performance, the Rinnai RXP199iN makes an excellent choice due to its high flow rate and reliability. Budget-conscious buyers will find the Rheem RTEX-24 offers impressive value, especially for smaller homes or apartments. Those looking for a premium, highly efficient model should consider the Rinnai RX180iN, which combines advanced features with durable construction. Beginners or homeowners with limited space might prefer compact electric options like the Rheem RTEX-08 or 12kW Electric Heater. Ultimately, matching your household size, fuel availability, and budget will guide you to the best fit.
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