The best tankless water heater system delivers on-demand, energy-efficient hot water for modern homes, ensuring comfort for busy families and individuals alike. Choosing the right model involves understanding fluctuating energy needs, varying flow rates, and the nuances of installation space. A poorly selected unit can lead to lukewarm showers, inadequate supply during peak demand, or even unnecessary energy waste, negating its primary benefits.
This roundup explores ten leading options, highlighting their unique features and advantages to help you find the perfect fit for your household’s hot water demands.
For the best tankless water heater system, consider models like the Rheem 18kW 240V Electric Tankless Water Heater, which features durable copper heating elements and advanced self-modulation. Alternatively, the Rinnai RX199iN Condensing Smart Sense Natural Gas/Propane unit offers indoor/outdoor installation flexibility and Smart Sense gas control for optimized performance.
Best Tankless Water Heater Systems at a Glance
| Image | Product | Buy |
|---|---|---|
Best Pick 1  | Rheem 18kW 240V Tankless Electric Water Heater, Gray Best for: Whole-home heating | Check Price |
Best Pick 2  | NEW Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane Best for: High-demand homes | Check Price |
Best Pick 3  | Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY Best for: Apartment living | Check Price |
Best Pick 4  | Westinghouse Tankless Water Heater Electric 14kW 240V, Instant On-Demand Hot Best for: Small spaces | Check Price |
Best Pick 5  | Stiebel Eltron Tankless Water Heater – Tempra 24 Plus – Best for: Family households | Check Price |
How We Picked
We rigorously evaluated top contenders to identify the best tankless water heater system for Our selection prioritized robust build quality and proven real-world performance, examining factors like heating element construction and modulation capabilities. Safety was paramount, leading us to favor models with advanced safety redundancies.
Durability, indicated by materials like copper and robust casings, also played a significant role. Standout features such as precise digital controls, smart self-modulation, and flexible installation options like indoor/outdoor versatility were key differentiators, ensuring we recommended truly superior units.
What Most Buyers Get Wrong
Understanding GPM for Your Household Needs
When choosing a tankless water heater, GPM (gallons per minute) is crucial for ensuring you have enough hot water for simultaneous uses. For a 2-3 bathroom home, a unit delivering around 7.0 GPM like the Rheem RTG-70XLN-3 can comfortably handle multiple hot water demands, such as a shower running while laundry is being done. Underestimating your GPM needs can lead to lukewarm water during peak usage, so assess your household’s typical hot water consumption carefully before making a decision.
Electric vs. Gas: Powering Your Hot Water
The choice between electric and gas tankless water heaters impacts installation and energy source. Electric models, like the Rheem 18kW (Rheem 18kW 240V) and Westinghouse 14kW (Westinghouse Tankless Water Heater Electric 14kW), offer simpler installation with direct electrical hookups but may require significant amperage. Gas models, such as the Rinnai RX199iN and Rheem RTG-70XLN-3, often provide higher flow rates and are powered by natural gas or propane.
Consider your existing utility infrastructure and potential energy costs when deciding which power source best suits your home.
1. Rheem 18kW 240V Tankless Electric Water Heater, Gray
Best for: Best for precise temperature control.
This Rheem unit features an external LED display with +/- 1 degree accuracy, allowing you to set your exact desired hot water temperature and achieve it consistently.
It provides up to 4.4 GPM in flow rate with durable copper heating elements. The 18kW, 240V electric heater uses self-modulation to adjust power based on hot water demand, and its two heating elements are field serviceable for easier maintenance.
Pros
- Precise temperature control via LED display
- Durable copper heating elements
- Self-modulating power adjustment
- Field serviceable heating elements
Cons
- Requires a dedicated 40A double-pole breaker for its 18kW heating capability.
This Rheem model is ideal for homeowners who need precise temperature control for their hot water needs. It’s suitable for those seeking consistent comfort and efficient operation.
2. NEW Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane
Best for: Best for flexible indoor/outdoor and fuel use.
The Rinnai RX199iN operates on either natural gas or propane, offering unparalleled flexibility for installation indoors or outdoors with its Versa Vent system.
This compact unit provides a significant flow rate of up to 11.1 GPM, capable of supplying up to 7 fixtures simultaneously. Its Smart Sense gas control system optimizes performance, and it’s compatible with smart home systems for modern convenience.
Pros
- Dual fuel capability (NG/Propane)
- Indoor/outdoor installation flexibility
- High flow rate of 11.1 GPM
- Smart Sense gas control system
Cons
- An RX-OVC vent cap is required for outdoor installations, adding an extra purchase.
This Rinnai is perfect for homeowners needing versatile installation options and the ability to use either natural gas or propane. It’s a powerful solution for large households with simultaneous hot water demands.
3. Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY
Best for: Best for space-saving with moderate demand.
With a 13kW heating capacity and providing up to 4.8 GPM, this Rheem RTEX-13 unit is a compact solution for delivering on-demand hot water without a large tank.
It features a digital LED display for precise temperature adjustment in 1-degree increments and 99.8% energy efficiency. This electric heater includes 1/2 inch NPT adapters for simple installation and is designed with copper immersion heating elements.
Pros
- Compact and space-saving design
- Precise 1°F temperature control
- High energy efficiency (99.8%)
- Included NPT adapters for easy setup
Cons
- Requires two 40A breakers due to its 13kW power draw.
This Rheem model is an excellent choice for apartments, smaller homes, or point-of-use applications where space is a premium. It offers efficient on-demand hot water for moderate usage needs.
4. Westinghouse Tankless Water Heater Electric 14kW 240V, Instant On-Demand Hot
Best for: Best for smart home integration and Wi-Fi control.
This Westinghouse tankless electric water heater boasts smart home compatibility with Alexa and Wi-Fi, allowing for voice control and remote adjustments.
It delivers up to 3.38 GPM with an instantaneous flow and requires a 60-amp double-pole circuit breaker. The 14kW unit also comes with a 12-month warranty and ETL certification for added peace of mind.
Pros
- Smart Home and Wi-Fi enabled
- Instant on-demand hot water
- ETL Certified with warranty
- Works with Google Assistant and Alexa
Cons
- Has a lower maximum flow rate of 3.38 GPM, limiting simultaneous use on multiple fixtures.
This Westinghouse unit is perfect for tech-savvy homeowners who want convenient smart home integration. It’s well-suited for smaller households or point-of-use applications where 3.38 GPM is sufficient.
5. Stiebel Eltron Tankless Water Heater – Tempra 24 Plus –
Best for: Best for continuous flow and whole-house hot water.
The Stiebel Eltron Tempra 24 Plus uses patented Advanced Flow Control to automatically maintain your set water temperature, ensuring continuous hot showers even if demand spikes.
This 24kW electric heater provides endless hot water for an entire house without requiring venting, saving significant space. Its sleek design and auto-modulation contribute to its energy efficiency.
Pros
- Patented Advanced Flow Control
- Continuous hot water supply
- Space-saving design, no venting needed
- Automatic energy-saving modulation
Cons
- Requires a substantial electrical setup with multiple 40A breakers for its 24kW heating capacity.
This Stiebel Eltron model is ideal for larger homes with high hot water demands and multiple concurrent users. It’s designed for those who prioritize uninterrupted, comfortable hot water flow throughout the house.
6. BOSCH Electric Mini-Tank Water Heater Tronic 3000 T 2.5-Gallon (ES2.5)
Best for: Best for under-sink point-of-use applications.
The BOSCH Tronic 3000 T is a 2.5-gallon mini-tank designed for convenient point-of-use installations directly under your sink, providing immediate hot water.
With a 1440-watt heating element and 120V power, it easily plugs into a standard outlet for independent installation or can be used in-line with a larger system. Its glass-lined interior ensures long-lasting quality and easy maintenance.
Pros
- Compact 2.5-gallon capacity
- Point-of-use convenience
- Plugs into standard 120V outlet
- Durable glass-lined interior
Cons
- Limited capacity means it’s not suitable for supplying multiple fixtures or high-demand showers as a sole source.
This BOSCH mini-tank is perfect for kitchens or bathrooms where you need instant hot water at a single faucet. It’s an excellent solution to eliminate the wait for hot water at the tap.
7. Rinnai CX199iN Condensing Smart Sense Commercial Natural Gas or Propane
Best for: Best for commercial or high-demand gas use.
The Rinnai CX199iN offers super high efficiency with a 97% thermal rating on natural gas, designed for commercial or significant household hot water demands.
This unit provides an impressive flow rate of 11.1 GPM, capable of handling multiple simultaneous uses. It features a Smart Sense gas control system and can be installed indoors or outdoors, with a vent cap required for external use.
Pros
- High thermal efficiency (97%)
- Powerful 11.1 GPM flow rate
- Smart Sense gas control system
- Indoor/outdoor installation flexibility
Cons
- Outdoor installation requires the purchase of an additional RX-OVC vent cap.
This Rinnai model is engineered for demanding commercial applications or larger homes with very high hot water usage. It’s ideal for businesses or households that require consistent, high-volume hot water delivery.
8. Rheem RTG-70XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water
Best for: Best for outdoor installation with natural gas.
This Rheem RTG-70XLN-3 is specifically designed for outdoor installation, running on natural gas and delivering up to 7.0 GPM for multi-bathroom homes.
Powered by 160,000 BTUs, it ensures fast, reliable hot water even during peak demand, featuring a hot-start program to minimize cold water bursts. The unit includes self-diagnostic programming and freeze protection.
Pros
- Outdoor installation design
- 7.0 GPM flow rate
- 160,000 BTU natural gas power
- Hot-start programming included
Cons
- Requires professional installation by a qualified technician due to its natural gas and outdoor setup.
This Rheem unit is an excellent choice for homeowners who need a robust natural gas water heater installed outdoors. It’s suited for homes with 2-3 bathrooms requiring reliable hot water for showers and laundry.
9. EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240
Best for: Best for energy efficiency and apartment living.
The EcoSmart ECO 11 uses 13kW at 240V to deliver endless on-demand hot water while being 90% smaller than traditional tanks, making it ideal for saving space and energy.
It provides consistent performance within 1 degree of the selected temperature, with a flow rate of 3.1 GPM. The unit’s compact dimensions (11.5 x 8 x 3.75 inches) allow for easy wall or point-of-use installation.
Pros
- Energy efficient operation
- Space-saving compact design
- Precise temperature control (+/- 1°F)
- Consistent performance with controlled flow rates
Cons
- The 3.1 GPM flow rate may be insufficient for simultaneous use on multiple high-demand fixtures.
This EcoSmart ECO 11 is perfect for apartments, condos, or smaller homes where space is limited and energy efficiency is a priority. It’s designed for individuals or couples needing a reliable hot water source.
10. Electrolux 18kW Tankless Water Heater Electric 240v – Smart Wifi
Best for: Best for whole-house hot water with Wi-Fi control.
Electrolux’s 18kW tankless electric water heater provides instant hot water for the whole house and features Smart Wifi for convenient control and monitoring.
This unit operates at 240V and requires specific electrical configurations, including two 40A breakers and 8 AWG wires. It comes with a scale inhibitor and ETL certification for enhanced performance and durability.
Pros
- Whole-house instant hot water
- Smart Wifi and voice control enabled
- Comes with a scale inhibitor
- ETL Certified for safety and reliability
Cons
- Requires careful consideration of household electrical capacity, needing a panel of at least 150 amps for optimal operation.
This Electrolux model is suited for modern homes seeking a connected experience and reliable whole-house hot water. It’s designed for users who appreciate smart technology alongside efficient water heating.
Gas vs. Electric Throughput Limits Usage
When selecting a best tankless water heater system, the fundamental choice between gas and electric fuels dictates not just operating cost but, crucially, the system’s ability to meet simultaneous hot water demands. This is not a matter of preference; it is an absolute constraint on practical application. Gas units, exemplified by the Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane and the Rheem RTG-70XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water, leverage significantly higher energy input — measured in BTUs, like the 160,000 BTUs of the Rheem RTG-70XLN-3 — to achieve considerably higher flow rates, often exceeding 7.0 GPM.
This throughput is essential for households needing to run multiple fixtures, such as a shower and dishwasher, concurrently without a drop in temperature. Electric models, even powerful ones like the Rheem 18kW 240V Tankless Electric Water Heater or the Electrolux 18kW Tankless Water Heater Electric 240v, are fundamentally limited by electrical service capacity.
An 18kW unit, while robust for electric, often requires two dedicated 40A or 50A breakers, pushing the limits of standard residential electrical panels and still typically topping out around 3.5-4.0 GPM for a comfortable temperature rise. Smaller electric units, such as the Westinghouse Tankless Water Heater Electric 14kW 240V, will deliver even less, making them suitable for single-point-of-use applications or very conservatively used single bathrooms. The Stiebel Eltron Tankless Water Heater – Tempra 24 Plus, despite its advanced flow control, is still bound by its electrical wattage and subsequent GPM output.
Attempting to operate multiple high-demand fixtures on an electric unit that exceeds its capacity will result in lukewarm water, not the continuous hot supply promised.
This distinction becomes critical when evaluating the actual needs of a household versus the marketing specifications. A common pitfall is selecting an electric unit based solely on its kilowatt rating, assuming it will perform like a comparable BTU-rated gas unit. The Westinghouse 14kW, for instance, with its 3.38 GPM maximum flow rate, is a clear indicator that it cannot support simultaneous use in the way that a Rinnai CX199iN Condensing Smart Sense Commercial Natural Gas or Propane, designed for higher demand applications, can.
Similarly, the Rheem RTEX-13 Residential Tankless Water Heater, while offering precise temperature control, is limited by its 13kW electric rating, placing it firmly in the single-bathroom or point-of-use category. The EcoSmart ECO 11 Electric Tankless Water Heater, rated at 13KW, also falls within this GPM restriction for typical temperature rises.
Trying to push these electric units beyond their design flow rate for simultaneous use defeats the purpose and leads to customer dissatisfaction, a problem compounded by the fact that they can often be installed with simpler electrical configurations than required for gas venting.
The point-of-use exception, however, is where electric shines and gas is often overkill. The BOSCH Electric Mini-Tank Water Heater Tronic 3000 T 2.5-Gallon is ideal for under-sink applications where only a small, immediate supply of hot water is needed for a faucet or dispenser, eliminating the wait time from a central heater. It’s a dedicated solution for a specific problem, a marked contrast to the whole-house performance expected from the larger gas units or the higher-kW electric tankless models.
Therefore, understanding your simultaneous hot water demand is paramount. If you have a multi-person household with multiple bathrooms or consistently run high-demand appliances concurrently, a gas model like the Rheem RTG-70XLN-3 is likely the only viable option.
For single-bathroom homes or specific point-of-use needs, electric tankless units like the Rheem 18kW 240V or the EcoSmart ECO 11 can be perfectly adequate, provided their flow rate limitations are respected.
What to Look For in a Tankless Water Heater System
Fuel type: gas vs electric
For reliable and high-volume hot water, natural gas tankless water heaters are superior, demanding an input of at least 75,000 BTU for most homes. Electric models, while simpler to install, struggle with simultaneous demand and require significant amperage (often 40-60 amps per unit) and specific voltage (240V), making them best suited for single-point-of-use applications or smaller residences with moderate demand. Choose natural gas for whole-home heating needs and explore propane only if natural gas is unavailable, ensuring sufficient BTU input for your climate.
Flow rate gpm
Match the unit’s flow rate to your household’s peak demand. A typical single-family home needs at least 5 GPM, while larger households with multiple bathrooms and simultaneous water usage (e.g., shower and dishwasher running together) require 7 GPM or higher. Look for models explicitly stating their capacity at a 40°F temperature rise, as this is a standard measure.
Any unit falling below 5 GPM is for minimal use cases only. Select a 7 GPM unit or greater for assured comfort in most multi-bathroom homes.
Temperature control and rise
The ideal tankless heater achieves your desired temperature rise without faltering. For most regions, a 40°F rise is standard, but colder climates may necessitate a 60°F rise or higher. Prioritize models with precise digital thermostats, offering granular control down to the degree.
Avoid units without digital readouts, as their temperature accuracy is less reliable. A unit capable of a 60°F rise with digital precision guarantees adequate hot water even in the harshest winter conditions.
Ventilation requirements
Proper ventilation is paramount for safety and efficiency. Direct-vent units, drawing outside air and venting exhaust directly through a wall, are the safest and most common choice for efficient operation. Power-venting is an alternative when direct venting isn’t feasible, pushing exhaust gases through ductwork.
Always opt for stainless steel venting materials; they resist corrosion and ensure longevity. Any system lacking direct or power venting, particularly those using less durable materials, poses a significant safety risk and should be avoided for whole-home installations.
Which Should You Choose?
- If you need hot water for a single, low-demand fixture like a remote sink, choose a small, point-of-use mini-tank.
- If you have specific flow rate needs and limited electrical capacity, choose an electric unit with a specified GPM and amperage.
- If you want flexible indoor/outdoor installation and the option to switch fuel types, choose a condensing gas model with smart fuel sensing technology.
- If you’re looking for a whole-house solution with multiple hot water demands, choose a high-efficiency gas unit that can deliver a high GPM.
Quick Best Tankless Water Heater System Buying Checklist
- Fuel Type: Decide between natural gas, propane, or electric models based on your home’s infrastructure.
- Flow Rate (GPM): Calculate the gallons per minute needed to support your household’s simultaneous hot water demands.
- Temperature Rise: Ensure the unit can achieve the desired temperature increase even in colder climates.
- Energy Efficiency (UEF): Look for higher Uniform Energy Factor ratings to minimize long-term operating costs.
- Venting System: Confirm the type of venting required (direct or power) and its compatibility with your installation location.
- Warranty: Check the manufacturer’s warranty period for both the unit and its components.
Frequently Asked Questions
What Is The Primary Benefit Of A Tankless Water Heater System?
The primary benefit of a tankless water heater system is its continuous supply of hot water without running out, unlike traditional tank heaters. This on-demand heating also leads to significant energy savings by only heating water as needed, reducing standby energy losses.
How Does A Tankless Water Heater System Save Energy?
Tankless systems save energy by heating water only when a hot water tap is turned on, eliminating the constant energy expenditure of maintaining a large tank of hot water. This ‘on-demand’ heating process significantly reduces standby losses compared to conventional tank water heaters.
What Is Flow Rate In Relation To A Tankless Water Heater System?
Flow rate, measured in gallons per minute (GPM), indicates how much hot water the tankless system can deliver simultaneously. It’s crucial for ensuring enough hot water for multiple fixtures like showers and sinks operating at once without a drop in temperature.
Can A Tankless Water Heater System Handle Multiple Hot Water Demands?
Yes, a properly sized tankless water heater system can handle multiple hot water demands by delivering continuous hot water. The key is selecting a unit with a sufficient GPM flow rate to meet the peak demand of your household’s simultaneous usage.
What Is Temperature Rise For A Tankless Water Heater System?
Temperature rise is the difference between the incoming cold water temperature and the desired hot water output temperature. Tankless systems need to achieve an adequate temperature rise to provide sufficiently hot water, especially in colder regions or for high-demand applications.
Final Words
Upgrading to the best tankless water heater system offers unparalleled efficiency and endless hot water, transforming your daily routines. Enjoy consistent comfort while benefiting from substantial energy savings and a reduced environmental footprint. Make the switch today to experience the ultimate in water heating convenience and performance.