The best tankless water heater system provides an endless supply of hot water and significant energy savings for homeowners seeking efficiency and convenience. Choosing the right unit involves considering factors like flow rate, fuel type (electric vs. gas), and installation requirements to meet your household’s specific needs.
A misstep can lead to inadequate hot water during peak demand or an inefficient system that drives up utility bills. Understanding these nuances ensures you invest in reliability and performance that lasts.
Our curated list of top picks will help you navigate the market and find the perfect tankless water heater system for your home.
For those seeking the best tankless water heater system, prioritizing durable copper heating elements and advanced self-modulation for precise temperature control is key, as seen in models like the Rheem 18kW 240V Tankless Electric Water Heater. Alternatively, for continuous, consistent comfort, consider a unit with patented flow control technology, such as the Stiebel Eltron Tempra 24 Plus, which adjusts flow to maintain hot water demand.
Best Tankless Water Heater Systems: At a Glance
| Image | Product | Buy |
|---|---|---|
Best Pick 1  | Rheem 18kW 240V Tankless Electric Water Heater, Gray Best for: High-power homes | Check Price |
Best Pick 2  | NEW Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane Best for: Smart home integration | Check Price |
Best Pick 3  | Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY Best for: Smaller residences | Check Price |
Best Pick 4  | Westinghouse Tankless Water Heater Electric 14kW 240V, Instant On-Demand Hot Best for: DIY installations | Check Price |
Best Pick 5  | Stiebel Eltron Tankless Water Heater – Tempra 24 Plus – Best for: Apartment living | Check Price |
How We Picked
To identify the best tankless water heater system, we prioritized build quality, real-world performance, safety, durability, and standout features. We evaluated models like the Rheem 18kW and Rinnai RX199iN, scrutinizing their self-modulation capabilities, copper heating elements, and versatile installation options. Units with advanced temperature control, like the Stiebel Eltron Tempra 24 Plus, were favored for consistent comfort.
We considered flow rates and power requirements, like those from Westinghouse and EcoSmart, ensuring they meet practical demand. Ultimately, our selection process focused on delivering exceptional value and long-term reliability.
What Most Buyers Get Wrong
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Gauging Your Home’s Hot Water Demand
Tankless water heaters are sized by flow rate (GPM) and temperature rise. For example, a product like the Rheem RTG-70XLN-3 boasts up to 7.0 GPM, ideal for multiple simultaneous uses. Consider how many fixtures you might run at once—showers, dishwashers, washing machines.
A lower demand, like a single bathroom or point-of-use sink, might suffice with a smaller unit such as the Bosch Tronic 3000 T. Over-sizing is inefficient, while under-sizing leads to lukewarm disappointment.
Electric vs. Gas: Powering Your On-Demand Heat
The biggest decision is choosing between electric and gas. Electric models like the Rheem 18kW or EcoSmart ECO 11 offer simpler installation but require significant amperage, often needing dedicated, high-capacity circuits. Gas units, such as the Rinnai RX199iN or Rheem RTG-70XLN-3, typically offer higher flow rates and may be more cost-effective to operate depending on local utility prices.
Ensure your home has the necessary gas line or electrical capacity before choosing.
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1. Rheem 18kW 240V Tankless Electric Water Heater, Gray
Best for: Fastest flow for single-shower houses.
With copper immersion heating elements, this Rheem provides up to 4.4 GPM for immediate hot water delivery. Its two heating elements are field serviceable, allowing for straightforward replacements when needed.
The unit features an external digital thermostatic control with +/- 1-degree accuracy and self-modulation to match hot water demand. It operates at 18kW and 240V, with a maximum pressure of 150 PSI.
Pros
- Durable copper immersion heating elements
- Field serviceable elements for easy replacement
- Precise temperature control via digital display
- High flow rate for rapid hot water
Cons
- Requires two 240V/40A double-pole breakers and 8 AWG wires for installation.
This Rheem model is ideal for homes needing consistent, high-volume hot water for a single high-demand fixture. It’s suitable for those who prioritize easy maintenance and precise temperature control.
2. NEW Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane
Best for: Versatile indoor/outdoor gas for multiple simultaneous uses.
This Rinnai RX199iN unit is designed for installation virtually anywhere, indoors or out, and can run on natural gas or propane via its Smart Sense gas control system. It provides up to 11.1 GPM, enough for seven fixtures at once.
Measuring the size of a small suitcase, this condensing tankless water heater boasts an impressive 199,000 BTU heat output. It operates on 120V and is Smart Home Compatible.
Pros
- Dual fuel compatibility (NG/Propane)
- Indoor/outdoor installation flexibility
- High flow rate for whole-house demand
- Compact size for minimal space impact
Cons
- Requires a specific RX-OVC vent cap for outdoor installations.
This Rinnai is an excellent choice for homeowners or businesses requiring a flexible, high-capacity hot water solution. Its ability to run on two gas types makes it adaptable to various installation sites.
3. Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY
Best for: Precision temperature for sensitive users.
The Rheem RTEX-13 offers precise temperature adjustments in 1°F increments with its external digital thermostatic control and LED display. This model ensures hot water is delivered at your exact desired temperature, with +/- 1 degree accuracy.
With a 13kW wattage and 240V power, this unit provides a flow rate of 4.8 GPM. It’s 99.8% energy efficient and includes 1/2 NPT adapters for simple installation, connecting via 1/2 inch compression water connections.
Pros
- Precise 1-degree temperature adjustment
- High energy efficiency (99.8%)
- Simple installation with included adapters
- Compact design saves space
Cons
- The included water-saver shower head has a 1.5 GPM flow rate, which may be lower than desired for some.
This Rheem unit is perfect for precise temperature needs, such as households with young children or elderly individuals requiring consistent comfort. It’s also well-suited for smaller homes or apartments where space is a concern.
4. Westinghouse Tankless Water Heater Electric 14kW 240V, Instant On-Demand Hot
Best for: Smart home integration for on-demand heating.
The Westinghouse 14kW electric tankless water heater delivers on-demand hot water at up to 3.38 GPM, with a starting flow rate of just 0.5 GPM. Its Smart Home compatibility allows for voice control and Wi-Fi integration.
Operating at 240V, this unit requires one 60-amp (double-pole) circuit breaker and 6 AWG wire. It features a bottom 1/2-inch NPT water connection and comes with a 12-month warranty.
Pros
- Smart Home and Wi-Fi compatible
- Instant hot water delivery
- Low activation flow rate
- ETL Certified for safety
Cons
- Requires a dedicated 60-amp double-pole circuit breaker.
This Westinghouse heater is a smart choice for tech-savvy homeowners seeking convenient, on-demand hot water. Its integration capabilities make it ideal for automated homes.
5. Stiebel Eltron Tankless Water Heater – Tempra 24 Plus –
Best for: Continuous flow with advanced temperature stability.
Stiebel Eltron’s Tempra 24 Plus uses patented Advanced Flow Control technology to automatically maintain your set water temperature, even if demand exceeds capacity, by slightly reducing flow. This ensures hot showers are never interrupted.
This compact, sleek white unit provides endless hot water for an entire house without venting. It’s energy-efficient with auto-modulation and operates at 24kW and 240V, supporting a maximum pressure of 150 PSI.
Pros
- Advanced Flow Control for stable temperatures
- Continuous and endless hot water supply
- Space-saving, vent-free design
- Energy-efficient auto-modulation
Cons
- Requires hard wiring for installation.
This Stiebel Eltron model is best for larger homes or families who experience simultaneous hot water demands. The Advanced Flow Control is valuable for maintaining consistent shower temperatures under varied usage.
6. BOSCH Electric Mini-Tank Water Heater Tronic 3000 T 2.5-Gallon (ES2.5)
Best for: Point-of-use hot water for sinks.
The BOSCH Tronic 3000 T 2.5-gallon mini-tank water heater fits discreetly under your sink, providing convenient hot water exactly where and when you need it. Its 98% thermal efficiency contributes to energy savings.
This electric water heater operates at 1440 watts and 120 volts, plugging into a standard outlet for independent installation. It features premium glass-lined material for long service life and has dimensions of 13.75 W x 13.75 H x 10.75 D inches.
Pros
- Compact point-of-use design
- Easy 120V outlet installation
- Glass-lined interior for durability
- High thermal efficiency (98%)
Cons
- Limited 2.5-gallon capacity is not suitable for whole-house hot water.
This Bosch mini-tank is ideal for single-sink applications, such as a kitchen prep area or a home office bathroom, where immediate hot water is needed. It’s perfect for reducing wait times for hot water at that specific point.
7. Rinnai CX199iN Condensing Smart Sense Commercial Natural Gas or Propane
Best for: High-efficiency commercial-grade gas heating.
The Rinnai CX199iN commercial tankless water heater provides 11.1 GPM, with an impressive 96% thermal efficiency to significantly reduce operational costs. It’s designed for indoor/outdoor use with propane or natural gas.
This unit can be installed virtually anywhere thanks to its Versa Vent system and Smart Sense gas control. It has a maximum temperature of 185°F and a heat output of 199,000 BTUs, operating on 120V.
Pros
- Very high flow rate for commercial needs
- Excellent energy efficiency (96%)
- Flexible indoor/outdoor installation
- Dual fuel capability (NG/Propane)
Cons
- Requires a specific RX-OVC vent cap for outdoor installations.
This Rinnai unit is designed for businesses or multi-family dwellings with significant hot water demands. Its high efficiency and flexible installation make it a cost-effective commercial solution.
8. Rheem RTG-70XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water
Best for: Outdoor setup for 2-3 bathroom homes.
The Rheem RTG-70XLN-3 delivers up to 7.0 GPM, making it ideal for 2-3 bathroom homes with concurrent hot water needs like showers and laundry. Powered by natural gas with 160,000 BTUs, it ensures fast, reliable hot water even during peak demand.
This durable, non-condensing tankless unit is built for outdoor installation with a metal cabinet and easy wall mounting support. Features include a self-diagnostic program, hot-start programming, and freeze protection.
Pros
- High flow rate for multiple fixtures
- Fast, reliable hot water delivery
- Outdoor installation design
- Durable metal cabinet construction
Cons
- Requires outdoor installation and is powered by natural gas only.
This Rheem unit is specifically for homeowners with moderate to high hot water usage who prefer an outdoor installation. It efficiently serves households with two to three bathrooms simultaneously.
9. EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240
Best for: Compact, energy-efficient electric water heater.
The EcoSmart ECO 11 uses 13,000 watts to deliver endless, on-demand hot water, with water temperature continually monitored and controlled to within 1 degree of the selected setting. Its 90% smaller size than traditional tanks saves valuable wall space.
Operating at 220V, this electric tankless water heater offers a flow rate of 3.1 GPM. It can be installed on a wall or at a point of use, with dimensions of 11.5 x 8 x 3.75 inches.
Pros
- Space-saving compact design
- On-demand continuous hot water
- Precise temperature control
- Energy efficient operation
Cons
- Amperage draw is 54A, requiring significant electrical capacity.
This EcoSmart model is a great fit for apartments, small homes, or as a point-of-use heater where space is limited. It’s suitable for individuals or couples seeking on-demand hot water without a large footprint.
10. Electrolux 18kW Tankless Water Heater Electric 240v – Smart Wifi
Best for: Smart Wi-Fi control for whole-house heating.
Electrolux’s 18kW tankless water heater provides instant hot water for the whole house with Smart Wifi and voice control capabilities. It offers stable temperature control, ensuring a consistent hot water experience.
Operating at 240V, this unit requires two 40A double-pole breakers and 8 AWG wires. It comes with a scale inhibitor for longevity and ETL certification for safety. It provides instant hot water with 24/7 customer service available.
Pros
- Smart Wifi and voice control
- Instant, endless hot water for whole house
- Comes with scale inhibitor
- ETL Certified
Cons
- Requires significant electrical infrastructure (2 x 240V/40A breakers, 8 AWG wires).
This Electrolux heater is ideal for tech-forward homeowners who want smart control over their hot water system. It’s designed for the demands of a whole house and those who appreciate advanced features.
Gas vs. Electric Powering the Best Tankless Water Heater System
When selecting the best tankless water heater system, the fundamental power source—natural gas/propane versus electric—dictates its practical application and long-term cost. Gas units, exemplified by the Rinnai RX199iN Condensing and the Rheem RTG-70XLN-3 High Efficiency Non-Condensing, offer higher flow rates and can handle simultaneous demands from multiple fixtures more readily. The Rinnai units, in particular, boast versatility with their Smart Sense gas control systems and ability to be installed indoors or outdoors, a significant advantage for homes with limited exterior space or where venting is complex.
However, this power comes with the requirement for gas lines and proper ventilation, which can introduce installation complexities and upfront costs.
Electric models, such as the Rheem 18kW 240V Tankless Electric Water Heater and the Westinghouse Tankless Water Heater Electric 14kW 240V, present a simpler installation path, often requiring only electrical upgrades and plumbing connections. Their self-modulating power control, seen in both Rheem models, allows them to adjust energy consumption to match hot water demand, contributing to efficiency. The Rheem RTEX-13 Residential Tankless Water Heater also features a self-modulating control and detailed digital thermostatic adjustment for precise temperature management.
These units are ideal for point-of-use applications or smaller homes where simultaneous demand is less of a concern. The EcoSmart ECO 11 Electric Tankless Water Heater, with its 13KW rating, is another strong contender in this category, emphasizing continuous on-demand hot water.
The inherent limitation of electric tankless heaters, including the Westinghouse and EcoSmart models, often lies in their electrical demands. A 14kW unit like the Westinghouse requires a significant 59A current and a dedicated 60-amp double-pole circuit, while higher-draw models may necessitate multiple circuits, potentially straining existing household electrical infrastructure. This contrasts with gas units that leverage higher BTU input to achieve greater GPM output, making them better suited for larger homes with high hot water usage, such as the Rheem RTG-70XLN-3, which delivers up to 7.0 GPM.
While electric options like the Rheem 18kW and Electrolux 18kW offer substantial power, they are still bound by the electrical service limitations of the home.
The Stiebel Eltron Tankless Water Heater – Tempra 24 Plus stands out with its patented Advanced Flow Control technology, which aims to maintain consistent water temperature by slightly reducing flow if demand exceeds capacity, attempting to bridge the gap between electric limitations and user expectations for continuous hot water. For those prioritizing ease of installation and a smaller footprint, the BOSCH Electric Mini-Tank Water Heater Tronic 3000 T 2.5-Gallon serves a different purpose entirely as a point-of-use solution, fitting neatly under a sink rather than serving an entire home. Ultimately, the choice hinges on your home’s existing infrastructure and your specific hot water needs.
For households requiring consistent, high-volume hot water for multiple fixtures simultaneously, a natural gas unit like the Rinnai CX199iN Condensing Smart Sense Commercial is the more robust and often more cost-effective long-term solution.
How to Choose the Best Tankless Water Heater System
Fuel type and energy efficiency
When choosing between natural gas and electric tankless water heaters, prioritize your existing infrastructure and long-term savings. Natural gas units offer higher flow rates and lower operating costs, but require a gas line and specific venting, often vertical. Look for an Energy Factor (EF) rating above 0.95 for excellent efficiency, regardless of fuel type.
Electric models are simpler to install with no venting needed, making them ideal for smaller spaces or apartments, but they consume more electricity, so ensure your home’s electrical panel can handle the load. For most homes seeking robust performance and lower ongoing expenses, a high-efficiency natural gas model is the definitive choice.
Hot water capacity and demand
Determine your household’s hot water demands by considering the number of bathrooms and appliances that run simultaneously. A typical shower uses 2.5 gallons per minute (GPM), while a dishwasher might use 1.5 GPM. For a home with two or more active bathrooms, aim for a unit with a minimum flow rate of 7-10 GPM.
Consider the temperature rise needed; if your incoming water is very cold, you’ll require a heater with a higher GPM capacity at that temperature. For comprehensive coverage, a whole-home tankless system is superior to multiple point-of-use units, ensuring consistent hot water everywhere.
Select a whole-home unit rated for your peak GPM demand.
Installation considerations
The space and installation requirements for tankless water heaters vary significantly by model. Gas units, especially those with condensing technology, typically require more ventilation and a dedicated gas line, often necessitating vertical venting through a roof or side wall. Electric models are more compact and have no venting needs, making them easily adaptable to closets or smaller utility rooms.
Ensure your home has the necessary electrical capacity for electric models or the appropriate gas line size for gas units. While DIY installation is possible for some electric units, gas models and complex setups demand professional plumbing and venting expertise for safety and optimal performance; always engage a qualified professional for gas heater installation.
Which Should You Choose?
- If you need hot water for multiple appliances and bathrooms simultaneously, look for models with a high Gallons Per Minute (GPM) rating, typically above 7 GPM.
- If you have limited space or want hot water at a specific sink, consider a compact point-of-use mini-tank heater.
- If you’re looking for flexibility in installation location and fuel type, opt for a model that is rated for both indoor and outdoor use and can run on natural gas or propane.
- If you have a high demand for hot water and want precise temperature control, choose a model with advanced self-modulation and digital thermostatic control.
Quick Best Tankless Water Heater System Buying Checklist
- Assess Your Hot Water Needs Determine how many fixtures will run simultaneously.
- Consider Fuel Source Weigh the pros and cons of natural gas versus electric.
- Check Energy Factor (EF) Ratings Higher EF means greater efficiency and cost savings.
- Evaluate Flow Rate (GPM) Ensure the unit can meet your peak demand.
- Understand Installation Requirements Account for space, venting, and utility hookups.
- Read Reviews and Compare Models Look for reliability and user satisfaction.
Frequently Asked Questions
What Is The Primary Benefit Of A Tankless Water Heater System?
The primary benefit is on-demand hot water, meaning you get hot water precisely when you need it. This eliminates the standby energy losses associated with traditional tank heaters, leading to significant energy savings over time.
How Does A Tankless Water Heater System Differ From A Traditional Tank Heater?
Unlike traditional tank heaters that store and continuously heat water, a tankless system heats water as it flows through the unit. This results in continuous hot water supply and is generally more energy-efficient because water isn’t stored at temperature.
What Is The Typical Lifespan Of A Tankless Water Heater System?
A well-maintained tankless water heater system typically lasts between 15 to 20 years, which is considerably longer than traditional tank water heaters. Proper maintenance, including descaling, is crucial for maximizing its operational life.
Are Tankless Water Heater Systems More Energy-Efficient?
Yes, tankless water heater systems are generally more energy-efficient because they only heat water when needed, avoiding the energy waste from keeping a large tank of water hot 24/7. This ‘on-demand’ heating can significantly reduce utility bills.
What Factors Determine The Size Of Tankless Water Heater System Needed?
The required size depends on your household’s peak hot water demand, measured in gallons per minute (GPM). Consider how many fixtures (showers, faucets, appliances) will be used simultaneously and the desired temperature rise to select an appropriately sized unit.
Final Words
Investing in the best tankless water heater system offers continuous hot water, enhanced energy efficiency, and space savings. These modern units provide a reliable and convenient solution for household needs, ultimately leading to lower utility bills. Upgrade your home’s water heating and enjoy these benefits for years to come.