When choosing a 40-amp tankless water heater, you’re looking for a unit that can handle moderate hot water demand, such as for sinks, low-flow showers, or small residential applications. These heaters are perfect for point-of-use installations or smaller homes where space is limited, and you want energy-efficient water heating. Here are the best 40-amp tankless water heaters in 2024:
1. EcoSmart ECO 18 – Best Overall 40-Amp Tankless Water Heater
The EcoSmart ECO 18 is one of the most popular and efficient tankless water heaters operating on a 40-amp breaker. It delivers a flow rate of up to 4.4 GPM, which can support 2-3 low-flow fixtures simultaneously. This unit features self-modulating technology, which optimizes energy usage based on the hot water demand, ensuring energy efficiency. It’s perfect for small homes or point-of-use installations like bathroom sinks, kitchen sinks, and showers.
Key Features:
- Flow Rate: 1.8 to 4.4 GPM (depending on inlet water temperature)
- Power: 18 kW at 240V (draws 40 amps)
- Best For: Small homes, bathroom/kitchen sinks, low-flow showers
- Efficiency: 99.8% energy efficiency
- Self-Modulating Technology: Adjusts energy usage based on demand
- Temperature Range: 80°F to 140°F
- Compact Size: Saves space and is easy to install
Pros:
- High energy efficiency with self-modulating technology
- Can handle 2-3 low-flow fixtures at once
- Compact and ideal for smaller homes or point-of-use installations
- Long warranty on parts (lifetime for residential use)
- Easy to install
Cons:
- Performance decreases in colder climates with lower inlet water temperatures
- Not suitable for large households with high hot water demand
2. Stiebel Eltron DHC-E 12 – Best for Advanced Features
The Stiebel Eltron DHC-E 12 is a reliable, German-engineered tankless water heater that runs on a 40-amp breaker and delivers instant hot water for small homes or point-of-use applications. This model features Advanced Flow Control, which ensures a consistent temperature even when the demand fluctuates. It’s perfect for bathroom sinks, low-flow showers, or kitchen sinks in smaller homes.
Key Features:
- Flow Rate: Up to 3 GPM
- Power: 12 kW at 240V (draws 40 amps)
- Best For: Point-of-use applications, small homes, kitchen or bathroom sinks
- Efficiency: 99%
- Advanced Flow Control: Automatically adjusts water flow to maintain constant temperature
- Digital Temperature Control: Precise temperature adjustments from 68°F to 140°F
- Durable Construction: Built to last with minimal maintenance
Pros:
- Consistent temperature with advanced flow control
- Compact and durable, perfect for small homes or point-of-use applications
- High efficiency with low standby heat loss
- Easy to install and maintain
Cons:
- Lower flow rate than other models, so best for single or small fixtures
- Not ideal for homes needing high hot water output
3. Rheem RTEX-18 – Best for Multiple Fixtures
The Rheem RTEX-18 is a powerful 40-amp tankless water heater that can handle multiple fixtures in smaller homes or apartments. It features external digital thermostatic control, which allows precise temperature adjustment, and provides a flow rate of up to 4.4 GPM, making it perfect for two showers or multiple sinks running simultaneously. This model is compact, highly efficient, and great for homes with moderate hot water demand.
Key Features:
- Flow Rate: Up to 4.4 GPM
- Power: 18 kW at 240V (draws 40 amps)
- Best For: Small homes, multiple fixtures (showers and sinks)
- Efficiency: 99.8% energy efficiency
- External Digital Thermostatic Control: Precise temperature adjustment from 80°F to 140°F
- Durable Design: Commercial-grade construction for long-lasting performance
Pros:
- Can handle multiple fixtures, making it versatile for small homes
- Precise temperature control with digital display
- High flow rate for its size
- Compact and easy to install in tight spaces
- Energy-efficient with self-modulating technology
Cons:
- Not suitable for very large homes or high-demand applications
- Requires dedicated electrical circuit and installation by a professional
4. Bosch Tronic 3000 US12 – Best for Point-of-Use Applications
The Bosch Tronic 3000 US12 is a great option for point-of-use water heating, such as sinks or low-flow showers. It runs on 40 amps and provides up to 1.8 GPM, making it perfect for specific installations where you need instant hot water without waiting for the central system. This unit is compact, easy to install, and requires minimal maintenance.
Key Features:
- Flow Rate: Up to 1.8 GPM
- Power: 12 kW at 240V (draws 40 amps)
- Best For: Bathroom sinks, kitchen sinks, small applications
- Efficiency: High energy efficiency
- Compact Design: Ideal for tight spaces and point-of-use installations
- Easy Installation: Simple to install and maintain
Pros:
- Perfect for point-of-use water heating
- Compact and fits easily under sinks or in small spaces
- Instant hot water with minimal wait time
- Simple installation with 40-amp circuit
- Highly efficient with minimal energy loss
Cons:
- Low flow rate, only suitable for one fixture at a time
- Not ideal for whole-house use or high-flow fixtures
5. Eemax EEM24018 – Best for Energy Savings
The Eemax EEM24018 is another excellent option for 40-amp applications, offering a flow rate of up to 4.4 GPM. It features self-modulating technology, which ensures energy is only used when necessary, reducing electricity bills over time. This unit is great for small homes, apartments, or point-of-use setups where consistent hot water is needed for multiple fixtures at once.
Key Features:
- Flow Rate: Up to 4.4 GPM
- Power: 18 kW at 240V (draws 40 amps)
- Best For: Small homes, multiple fixtures
- Efficiency: 99% energy-efficient with self-modulating technology
- Temperature Control: Adjustable up to 140°F
- Compact Size: Fits easily into tight spaces
Pros:
- Energy-efficient with self-modulating technology
- Can support multiple fixtures at once
- Compact and space-saving design
- High flow rate for its size
- Easy to install and maintain
Cons:
- Not suitable for large homes with high water demand
- Requires electrical upgrades for some installations
Comparison Table: Best 40-Amp Tankless Water Heaters
| Model | Best For | Flow Rate (GPM) | Power (kW) | Key Features | Price Range |
|---|---|---|---|---|---|
| EcoSmart ECO 18 | Small homes, low-flow showers | 1.8-4.4 GPM | 18 kW | Self-modulating tech, energy-efficient, compact | $$ |
| Stiebel Eltron DHC-E 12 | Point-of-use, advanced features | 3.0 GPM | 12 kW | Advanced Flow Control, durable, consistent temperature | $$ |
| Rheem RTEX-18 | Multiple fixtures, small homes | 4.4 GPM | 18 kW | Digital temperature control, high flow rate | $$$ |
| Bosch Tronic 3000 US12 | Point-of-use, small fixtures | 1.8 GPM | 12 kW | Compact, efficient, easy to install | $$ |
| Eemax EEM24018 | Energy savings, small homes | 4.4 GPM | 18 kW | Self-modulating, compact, supports multiple fixtures | $$ |
What to Look for in a 40-Amp Tankless Water Heater
- Flow Rate (GPM):
- For 40-amp tankless water heaters, you can expect flow rates ranging from 1.8 to 4.4 GPM. This is ideal for small homes, apartments, or point-of-use applications like kitchen sinks or low-flow showers.
- Power Output (kW):
- 40-amp units typically range between 12 and 18 kW, which is sufficient for smaller setups or moderate hot water needs. If you need to run multiple fixtures, opt for the higher end of this range.
- Energy Efficiency:
- Look for units with self-modulating technology (like the EcoSmart ECO 18 and Eemax EEM24018) to ensure maximum energy savings. This feature adjusts energy usage based on the demand for hot water.
- Installation Requirements:
- 40-amp tankless water heaters require 240V circuits and often dedicated electrical circuits. Be sure your home’s electrical system can handle this before purchasing.
- Application:
- Consider whether you need the unit for a single point-of-use (like a sink or shower) or for multiple fixtures. Models like the Rheem RTEX-18 and EcoSmart ECO 18 can handle multiple low-flow fixtures, while smaller models like the Bosch Tronic 3000 are better suited for single-use applications.
Final Recommendations
- For the best overall performance, the EcoSmart ECO 18 offers excellent energy efficiency and can handle multiple low-flow fixtures simultaneously.
- If you’re looking for advanced features and long-term durability, the Stiebel Eltron DHC-E 12 is a solid option with consistent temperature control.
- For homes needing to run multiple fixtures, the Rheem RTEX-18 delivers a high flow rate with precise temperature control, making it perfect for small homes or apartments.
- For point-of-use water heating with simple installation, the Bosch Tronic 3000 US12 provides reliable hot water for small fixtures like sinks.
- If energy savings is your top priority, the Eemax EEM24018 with self-modulating technology offers a compact design and the ability to support multiple fixtures in a small home or apartment.
Choosing the right 40-amp tankless water heater will ensure instant hot water where you need it, while also maximizing energy efficiency and space savings.