If you’re searching for a tankless water heater, you’re probably looking for a way to save space, reduce energy costs, or get hot water on demand. The EcoSmart ECO 11 stands out as the best overall choice for small households seeking efficient electric operation. For those needing high flow rates, the Rinnai RXP199iN offers impressive capacity with smart features. Meanwhile, the Rheem RTGH Series provides a robust gas option for larger homes. Keep in mind, the main tradeoffs involve upfront cost, installation complexity, and fuel type. Read on for a full breakdown of these options and what makes each one unique.
Key Takeaways
- Electric tankless heaters are budget-friendly but generally have lower flow rates, suitable for small households or point-of-use needs.
- Gas models like Rinnai and Rheem excel in high flow capacity, ideal for larger homes but come with higher installation and maintenance costs.
- Flow rate and temperature rise are critical; choosing a model that matches your household’s hot water demand prevents underperformance.
- Smart features and digital controls are increasingly common, offering better usability but often at a premium price.
- Installation considerations—venting, space, and fuel access—are vital to ensure proper operation and safety.
| tankless water heater | Flow Rate | Power | Voltage | Installation |
|---|---|---|---|---|
| EcoSmart ECO 11 Electric Tankl | 1.3 to 3.1 GPM | 13KW | 240V | — |
| Tankless Electric Water Heater | 0.3-0.5 GPM | 3000W | 110V | — |
| 18kW Tankless Water Heater Ele | 4.9 GPM | 18kW | 240V | — |
| Rinnai RXP199iN Condensing Sma | 11.1 GPM | — | — | Indoor/Outdoor |
| Rheem 18kW 240V Tankless Elect | up to 4.4 GPM | 18kW | 240V | Bottom 3/4 inch NPT connections |
| Rinnai RX199iN Condensing Smar | 11.1 GPM | — | — | Indoor/Outdoor |
| Rheem RTGH Series 8.4 GPM Natu | 8.4 GPM | — | — | Indoor, direct vent |
| Tankless Electric Water Heater | — | 3000W | 110V | Vertical only |
| Rheem 240V Tankless Water Heat | up to 3.17 GPM | 13kW | 240V | — |
| Rheem RTEX-08 8kW Professional | up to 1.95 GPM | 8kW | 240V | — |
| Rheem 11kW Multi Fixture Tankl | up to 2.68 GPM | 11kW | 240V | Requires professional wiring |
| Rinnai RX180iN Condensing Smar | 10 GPM | — | — | Indoor/Outdoor |
| Rheem RTEX-24 24kW 240V Electr | up to 5.9 GPM | 24kW | 240V | Requires professional wiring |
More Details on Our Top Picks
EcoSmart ECO 11 Electric Tankless Water Heater, 13KW, 240V
The EcoSmart ECO 11 stands out for its space-saving design and high efficiency, making it ideal for small bathrooms or sinks where space is limited. Compared with larger units like the Rinnai RXP199iN, it offers a lower flow rate, which means it’s best suited for low-demand applications and won’t support multiple fixtures simultaneously. Its self-modulating technology helps maintain consistent temperatures while reducing energy costs, but it may require a dedicated circuit and professional installation due to its electrical demands. This model excels in small-scale use but isn’t designed for larger households or high-flow needs.
Pros:- Compact, space-saving design perfect for small spaces
- High thermal efficiency at 99%
- Provides continuous hot water on demand
Cons:- Limited flow rate restricts use to low-demand applications
- Electrical installation can be complex and may require professional wiring
Best for: Single fixture applications like bathroom sinks or small offices where space and energy efficiency are priorities.
Not ideal for: Homes with multiple simultaneous hot water demands, as its flow rate is limited to about 1.3-3.1 GPM.
- Power:13KW
- Voltage:240V
- Amperage:54A
- Dimensions:11.5 x 8 x 3.75 inches
- Flow Rate:1.3 to 3.1 GPM
Our verdict“This pick is ideal for those needing a small, energy-efficient unit for low-flow applications, not for high-demand households.”
Tankless Electric Water Heater 110V, 3000W with Digital Display, Under Sink Instant Hot Water Heater
This 110V electric water heater offers instant hot water with a simple digital display and multiple safety features, making it a top choice for apartment dwellers, RV owners, or those needing a quick hot water boost. Unlike the EcoSmart ECO 11, it operates at a lower power level but compensates with a compact, lightweight design that fits easily under sinks or in tight spaces. It’s straightforward to install if you have appropriate electrical wiring, but flow rate is limited to about 0.3-0.5 GPM, making it unsuitable for larger households or multiple fixtures at once. Its waterproof protections and safety features add reliability for small-scale use.
Pros:- Compact, lightweight design ideal for tight spaces
- Instant hot water with quick temperature rise
- Multiple safety protections ensure reliable operation
Cons:- Flow rate may be too low for larger households
- Proper electrical wiring and circuit breaker setup are necessary
Best for: RVers, apartment renters, or anyone needing instant hot water in a small, accessible space.
Not ideal for: Multiple fixture use or homes with high hot water demands, due to its limited flow rate and capacity.
- Voltage:110V
- Power:3000W
- Flow Rate:0.3-0.5 GPM
- Temperature Rise:82°F to 131°F
- Protection:IPX4 waterproof, leak, dry-burning, over-temperature
Our verdict“This model makes the most sense for small-scale, quick hot water needs where space and safety are priorities, not high-volume household use.”
18kW Tankless Water Heater Electric, NOVIEEX 240V 3s Instant Hot Water Heater, Flow Rate Max 4.9 GPM, Supply for 2-3 Points, Indoor Installation
The NOVIEEX 18kW unit offers a high flow rate up to 4.9 GPM, making it suitable for small to medium homes where multiple fixtures might need hot water simultaneously. Compared with the EcoSmart ECO 11, it provides a significantly higher capacity, supporting 2-3 fixtures at once, thanks to its 18 kW power rating. Its digital temperature control and safety features make operation precise and reliable, though installation requires professional electrical wiring and specific breaker setups, which could increase initial costs. This model balances power and compact design well, but isn’t ideal for larger households or those without suitable electrical infrastructure.
Pros:- High flow rate suitable for multiple fixtures
- Precise digital temperature control
- Space-efficient wall-mount design
Cons:- Requires professional electrical installation
- Limited to small-to-medium-sized homes
Best for: Small to medium households seeking reliable hot water for multiple fixtures with space-saving design.
Not ideal for: Homes with high hot water demands or lacking dedicated electrical capacity, as installation can be complex.
- Power:18kW
- Voltage:240V
- Flow Rate:4.9 GPM
- Suitable for:2-3 points
- Safety Certifications:8-in-1 safety features
Our verdict“This pick suits families needing dependable hot water for several fixtures without sacrificing space, assuming proper electrical wiring is available.”
Rinnai RXP199iN Condensing Smart Sense Tankless Water Heater – 11.1 GPM, 199k BTU, Indoor/Outdoor, NG or Propane
The Rinnai RXP199iN excels in high-flow applications, supporting up to 11.1 GPM for large households or commercial use, unlike the smaller electric options. Its condensing technology offers excellent energy efficiency with a UEF of 0.98, making it more economical over time. The ability to install outdoors or indoors adds flexibility, and smart recirculation features enhance efficiency and convenience. However, its higher initial cost and the need for professional installation, including venting for outdoor use, may be a barrier for some. This unit is best suited to larger homes with multiple bathrooms and high hot water demand, not small apartments or low-flow needs.
Pros:- High flow rate up to 11.1 GPM supports multiple fixtures
- Flexible installation indoors or outdoors
- Smart recirculation technology for efficiency
Cons:- Higher initial investment and installation complexity
- WiFi control module sold separately
Best for: Large households or small commercial setups needing high hot water capacity and smart energy management.
Not ideal for: Small apartments or single fixture use, as its high capacity exceeds minimal needs and involves higher upfront costs.
- Flow Rate:11.1 GPM
- BTU:199,000
- Installation:Indoor/Outdoor
- Fuel Type:NG or Propane
- Warranty:15-year heat exchanger, 5-year parts
Our verdict“This model is ideal for large households seeking high capacity and smart features, with higher upfront costs being a tradeoff.”
Rheem 18kW 240V Tankless Electric Water Heater, Gray
The Rheem 18kW electric heater offers precise temperature control with its digital LED thermostat, making it suitable for those who want customizable hot water output. Its self-modulating technology helps optimize energy use, unlike simpler models that lack this feature. The durable copper heating elements are field replaceable, adding to its longevity. Compared to the EcoSmart ECO 11, it provides a higher flow rate of up to 4.4 GPM, making it more suitable for small households with multiple fixtures. However, it still requires professional installation and may not support high-demand scenarios, which limits its utility for larger families.
Pros:- Digital thermostat with LED display for accuracy
- Self-modulating technology improves efficiency
- Field-serviceable copper heating elements
Cons:- Requires professional electrical installation
- Flow rate may limit capacity for larger households
Best for: Small households or individuals wanting precise temperature control and durable components in their electric heater.
Not ideal for: Large households or high-flow applications, due to flow rate limitations and electrical requirements.
- Power:18kW
- Voltage:240V
- Flow Rate:up to 4.4 GPM
- Installation:Bottom 3/4 inch NPT connections
- Heating Elements:Copper immersion, field serviceable
Our verdict“This unit is perfect for small households prioritizing control and durability, but not for high-demand or large-family needs.”
Rinnai RX199iN Condensing Smart Sense Tankless Water Heater, 11.1 GPM, 199k BTU, Indoor/Outdoor, Supports Natural Gas or Propane
This model stands out for its impressive flow rate of 11.1 GPM, making it ideal for large households or homes with multiple bathrooms. Its support for both natural gas and propane adds flexibility, unlike the Rheem RTEX-13, which is limited by its lower flow capacity. The compact size and indoor/outdoor installation options give it a versatile edge, but professional installation and the need for a separate WiFi module can be hurdles for some users. The high energy efficiency (UEF 0.98) helps reduce utility bills, and the 15-year heat exchanger warranty offers peace of mind. Compared with other models, its capacity and support for different gas types make it a well-rounded choice for demanding applications.
Pros:- High flow rate of 11.1 GPM for simultaneous use
- Supports both natural gas and propane
- Energy-efficient with UEF 0.98
- Indoor and outdoor installation options
Cons:- Requires professional installation, adding upfront cost
- WiFi control module sold separately, complicating smart features
- Needs vent cap for outdoor use, adding installation steps
Best for: Homeowners with large families or high hot water demand needing installation flexibility
Not ideal for: Small apartments or single-user households where lower flow rates suffice, as the size and cost may be unnecessary
- Flow Rate:11.1 GPM
- BTU:199,000
- Gas Type:Natural Gas or Propane
- Installation:Indoor/Outdoor
- Energy Efficiency:UEF 0.98
- Warranty:15-year on heat exchanger, 5-year on parts and labor
Our verdict“This pick suits large households or demanding setups that value capacity and versatility over simplicity.”
Rheem RTGH Series 8.4 GPM Natural Gas Tankless Water Heater Indoor, 157,000 BTUs, High Efficiency, Condensing, Ultra-Low NOx
Compared with the Rinnai RX199iN, the Rheem RTGH offers a slightly lower flow rate of 8.4 GPM, but excels in high energy efficiency and ultra-low NOx emissions, making it suitable for eco-minded families. Its condensing technology ensures high efficiency, yet requires proper venting and indoor space, which may limit installation options. The digital temperature control with ±1°F precision makes it easy to set and maintain hot water, ideal for households with high demand. However, its flow rate may fall short for very large households or simultaneous multiple fixtures, which makes it less appropriate for those needs. Still, for eco-conscious consumers looking for reliable, efficient performance, this model delivers a compelling balance of features.
Pros:- High energy efficiency with condensing tech
- Ultra-low NOx emissions for eco-friendliness
- Precise digital temperature control
- Reliable for continuous hot water
Cons:- Lower flow rate limits simultaneous use
- Indoor installation and venting required
- Vents and space considerations may add complexity
Best for: Families seeking energy efficiency and environmentally friendly operation with consistent hot water
Not ideal for: Homes with very high simultaneous hot water needs or larger households requiring more GPM
- Flow Rate:8.4 GPM
- BTUs:157,000
- Efficiency:0.93 UEF
- Installation:Indoor, direct vent
- Emissions:Ultra-Low NOx
- Warranty:15-year heat exchanger, 5-year parts
Our verdict“This unit works best for eco-conscious households prioritizing efficiency over maximum flow capacity.”
Tankless Electric Water Heater 110V, 3000W with Digital Display
This electric tankless heater excels at providing instant hot water in small, confined areas like under sinks or in RVs, thanks to its compact design and 3000W power. It heats water on demand without preheating, unlike larger electric models that require bulky tanks. Its safety features, including leakage and overheating protection, add peace of mind for DIY installation. However, its flow rate of just 0.3 to 0.5 GPM limits it to small fixtures—this isn’t suitable for showers or multiple outlets. The vertical-only installation can restrict placement options, and water temperature varies with flow rate, which may require fine-tuning for comfort. Still, for quick, localized hot water, this unit performs well.
Pros:- Instant hot water with no preheat delay
- Compact, space-efficient design
- Safety features for peace of mind
- Easy to install
Cons:- Flow rate limited to small fixtures
- Vertical installation only, restricting placement
- Water temperature varies with flow rate
Best for: Apartment dwellers or RV owners needing instant hot water at a single fixture
Not ideal for: Large households or high-demand applications requiring higher GPM
- Power:3000W
- Voltage:110V
- Water Flow Rate:0.3 GPM (82°F), 0.5 GPM (131°F)
- Material:ABS
- Protection Features:Water and electricity isolation, IPX4 waterproof
- Installation:Vertical only
Our verdict“This pick is perfect for localized, point-of-use hot water in small spaces or for RVs where space is limited.”
Rheem 240V Tankless Water Heater RTEX-13, Gray
Compared with larger electric models like the NOVIEEX 18kW, the Rheem RTEX-13 offers a modest flow rate of up to 3.17 GPM, making it suitable for small households or single fixtures. Its digital temperature control and durable copper heating elements provide reliable performance, but the limited flow rate restricts its use for multiple outlets simultaneously. The simplified installation and 99.8% efficiency make it an attractive choice for those on a tighter budget or with limited space. Nevertheless, electrical requirements mean a dedicated 240V circuit is necessary, which could add to the installation complexity. For small-scale applications, this model balances affordability and functionality well.
Pros:- Digital temperature control with LED display
- High efficiency at 99.8%
- Durable copper heating elements
- Easy to install with included adapters
Cons:- Limited flow rate of 3.17 GPM
- Requires 240V electrical setup
- Not suitable for multiple simultaneous fixtures
Best for: Singles or couples needing reliable hot water for one or two fixtures without high flow demands
Not ideal for: Large families or homes with multiple bathrooms requiring higher GPM
- Voltage:240V
- Flow Rate:up to 3.17 GPM
- Power:13kW
- Efficiency:99.8%
- Model:RTEX-13
- Warranty:Not specified
Our verdict“This model is an excellent choice for small households or single fixtures where budget and space are priorities.”
Rheem RTEX-08 8kW Professional Classic 240V Tankless Electric Water Heater
With a modest 8kW power capacity, the Rheem RTEX-08 is tailored for very low-demand applications, such as under-sink or single fixture use. Its digital temperature display and self-modulating control simplify operation, but the flow rate of only 1.95 GPM limits its capacity to handle multiple outlets or showers. The 240V requirement means electrical setup must be considered during installation. Compared to higher-powered electric models, this unit excels in affordability and simplicity but falls short when larger flow rates are needed. It’s best suited for specific, small-scale points of use rather than whole-house solutions, making it a practical choice for budget-minded consumers with limited hot water needs.
Pros:- Adjustable digital temperature control
- Self-modulating power for efficiency
- On-demand hot water without preheating
- Easy to install with standard connections
Cons:- Limited flow rate of 1.95 GPM
- Requires 240V electrical supply
- Not suitable for multiple fixtures at once
Best for: Single fixture or point-of-use applications where low flow rate is acceptable
Not ideal for: Whole-house hot water supply or households with multiple simultaneous fixtures
- Power:8kW
- Voltage:240V
- Flow Rate:up to 1.95 GPM
- Water Connections:1/2″ NPT
- Digital Control:Yes
- Self-Modulating:Yes
Our verdict“This heater works well for small, single-point applications but isn’t designed for larger household demands.”
Rheem 11kW Multi Fixture Tankless Electric Water Heater – 240V
This Rheem model stands out for its compact size and energy-efficient operation, making it ideal for households with limited space that need to run multiple fixtures simultaneously. Compared with larger units like the Rinnai RX180iN, it offers a lower flow rate of up to 2.68 GPM, which means it’s better suited for small to medium households or point-of-use applications rather than whole-home solutions. Its main tradeoff is the need for a dedicated 240V electrical circuit, which might require professional wiring, and its limited flow rate could be a bottleneck during peak usage. However, its space-saving design and quick-on-demand heating make it a practical choice for apartments or small houses where only a few fixtures are used at once. If your hot water needs are modest and space is tight, this model is a strong fit.
Pros:- Compact, space-saving design ideal for small areas
- Energy-efficient, heats water only when needed
- Suitable for multiple fixtures with moderate flow demands
Cons:- Requires professional installation and specific electrical wiring
- Limited flow rate may not meet high demand during peak times
Best for: Small households or apartments needing space-efficient, multi-point hot water solutions
Not ideal for: Large families or homes with substantial hot water demands where higher flow rates are necessary
- Power:11kW
- Voltage:240V
- Flow Rate:up to 2.68 GPM
- Temperature Range:80°F – 140°F
- Warranty:5-Year Leak, 1-Year Parts
- Installation:Requires professional wiring
Our verdict“This model is best for small households or apartments seeking a compact, efficient solution for multiple fixtures with modest flow needs.”
Rinnai RX180iN Condensing Smart Sense Tankless Water Heater, 10 GPM, 180k BTU, Supports Natural Gas or Propane, Indoor/Outdoor
This Rinnai model makes a compelling case for larger households or those seeking versatile installation options, supporting up to 10 GPM—significantly higher than the Rheem 11kW electric unit—making it suitable for whole-home use. Its high efficiency of UEF 0.98, support for both natural gas and propane, and indoor/outdoor installation options give it a clear edge over less flexible models like the Rheem RTEX-24, especially for homes with diverse fuel sources or outdoor needs. The tradeoff is that professional installation and venting are necessary, which can add to upfront costs, and the WiFi control module is sold separately, which might be a drawback for tech enthusiasts. Nevertheless, for those wanting a high-capacity, durable unit that can be installed almost anywhere, this Rinnai model offers unmatched versatility and long-term value.
Pros:- Supports high flow rates up to 10 GPM for whole-house use
- Flexible installation options—indoor and outdoor
- Supports both natural gas and propane, offering fuel flexibility
- High energy efficiency with UEF 0.98
Cons:- Requires professional installation and venting
- WiFi control sold separately, adding extra cost
- Higher initial investment compared to smaller units
Best for: Larger households or homes requiring high hot water flow with flexible installation options
Not ideal for: Small apartments or single fixtures where high capacity isn’t needed, due to its size and cost
- 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/labor
Our verdict“This unit is ideal for large homes needing reliable, high-capacity hot water with flexible placement options.”
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater
The Rheem RTEX-24 offers a balanced approach with a flow rate up to 5.9 GPM, making it a solid choice for mid-sized households. Its standout feature is the digital temperature display and self-modulating power control, which helps maintain a precise output and improve energy efficiency over fixed-output models like the Rheem 11kW. Compared with the Rinnai RX180iN, it provides a lower flow rate but is easier to install and more suitable for homes where hot water demand is moderate. The tradeoff is that it still requires a dedicated 240V electrical supply, and during peak demand, the flow may fall short for larger households. This model works well for those who want control and reliability without the complexity or cost of gas models.
Pros:- Digital temperature display for precise control
- Self-modulating power for energy efficiency
- Provides continuous hot water without fluctuations
Cons:- Flow rate may be insufficient for large households
- Requires dedicated 240V electrical circuit
- Installation might need professional help
Best for: Households seeking precise temperature control and reliable hot water for moderate demand
Not ideal for: Large families or homes with simultaneous high hot water needs, as flow rate may be limiting
- Power:24kW
- Voltage:240V
- Flow Rate:up to 5.9 GPM
- Connections:Bottom 3/4″ NPT
- Temperature Control:Digital
- Installation:Requires professional wiring
Our verdict“This heater suits homes that value precise temperature control and moderate flow for everyday hot water needs.”
How We Picked
The products in this roundup were selected based on their performance, build quality, usability, and value. I prioritized models that serve a variety of household sizes and needs, from point-of-use electric units to whole-house gas systems. Each choice reflects a balance between capacity, efficiency, and cost, with an eye toward durability and ease of installation. The ranking considers customer reviews, expert ratings, and the features that influence real-world usability, such as flow rate, temperature control, and energy efficiency.| tankless water heater | Installation |
|---|---|
| EcoSmart ECO 11 Electric Tankl | — |
| Tankless Electric Water Heater | — |
| 18kW Tankless Water Heater Ele | — |
| Rinnai RXP199iN Condensing Sma | Indoor/Outdoor |
| Rheem 18kW 240V Tankless Elect | Bottom 3/4 inch NPT connections |
| Rinnai RX199iN Condensing Smar | Indoor/Outdoor |
| Rheem RTGH Series 8.4 GPM Natu | Indoor, direct vent |
| Tankless Electric Water Heater | Vertical only |
| Rheem 240V Tankless Water Heat | — |
| Rheem RTEX-08 8kW Professional | — |
| Rheem 11kW Multi Fixture Tankl | Requires professional wiring |
| Rinnai RX180iN Condensing Smar | Indoor/Outdoor |
| Rheem RTEX-24 24kW 240V Electr | Requires professional wiring |
