Best Electric Tankless Water Heaters for Bathtubs and More
For homeowners seeking on-demand hot water for bathtubs, sinks, and showers, electric tankless water heaters offer compact, energy-efficient options without the bulk of traditional tanks. This guide highlights top models that deliver reliable hot water, fast recovery, and easy installation in American homes. Each selection balances GPM capacity, energy efficiency, and user-friendly features to help you choose the right unit for a bathtub-focused setup.
Summary of chosen products
- Orbek 18kW Electric Tankless Water Heater — Up to 4.17 GPM, 2-3 fixtures, indoor
- Rheem 18kW 240V Tankless Electric Water Heater — Up to 4.4 GPM, digital control
- Orbek 14kW Tankless Water Heater — Up to 3.38 GPM, compact and LED display
- EcoSmart ECO 11 — 13 kW, self-modulating, compact and space-saving
Orbek 18kW Tankless Electric — Instant Hot Water
The Orbek 18kW unit is designed for quick on-demand hot water with a stated maximum flow of 4.17 GPM, making it suitable for 2-3 fixtures simultaneously. It requires 2 x 240V/40A circuits, 3/4″ NPT connections, and dedicated wiring. The system employs water-electricity separation to reduce scale buildup and corrosion, delivering hot water within seconds and potentially lowering electricity costs versus tank-style heaters when used efficiently.
Key features include: dual-pole 240V power, 4.17 GPM capacity, fast on-demand water, ETL certification, and indoor installation suitability. The unit emphasizes comfort across multiple outlets at once and emphasizes energy-conscious operation. Users planning to run a bath and a sink at the same time can benefit from its simultaneous delivery capability while maintaining stable temperatures.
Considerations: ensure available electrical service can support two 40A circuits, verify plumbing matches 3/4″ NPT, and plan for proper ventilation and space. The 3-second temperature stabilization is marketed as a strength, though actual performance can vary with inlet water temperature and distance to fixtures.
Rheem 18kW 240V Tankless Electric — Digital Control
The Rheem 18kW model uses external digital thermostatic control with an LED display, allowing precise temperature management to within about one degree. It features self-modulating technology to adjust power demand to the hot water load, improving efficiency. Durable copper immersion heating elements provide reliable service, and the unit is marketed as field serviceable for convenient maintenance. With a maximum flow of around 4.4 GPM, this unit is positioned for whole-home or multi-point use in mid-sized homes.
Considerations: ensure your electrical panel can accommodate multiple heating elements—often two 40A breakers—and confirm space for installation near main water lines. The self-modulating design helps manage energy use in response to demand, which can reduce standby losses compared to older tank heaters. The user interface with an LED readout aids quick adjustments during first-time setup.
Orbek 14kW Tankless Electric — LED Display
The Orbek 14kW unit provides up to 3.38 GPM of hot water and uses a 240V/60A two-pole breaker. It includes a LED digital display for easy temperature monitoring and supports 2-3 points of use with rapid recovery. The installer notes emphasize minimal energy costs due to water-electricity separation and quick 3-second response to hot water demand. The model is compact, making it versatile for apartments or smaller bathrooms where space is at a premium.
Considerations: check electrical service capacity and confirm you have a 60A circuit and appropriate gauge wiring. While the unit targets 2-3 points of use, performance will depend on inlet water temperature and plumbing length from the heater to fixtures. LED readout can simplify initial setup and ongoing adjustments for stable bathtub temperatures.
EcoSmart ECO 11 Electric Tankless Heater — Compact and Efficient
The EcoSmart ECO 11 is a smaller 13 kW option designed for 240-volt systems with self-modulating technology. It claims to provide endless hot water with continuous flow and monitors water temperature to maintain performance within one degree of the selected setpoint. The unit is notably compact—about the size of a small suitcase—and can be installed on a wall or at the point of use, which is advantageous in bathrooms where space is limited. It emphasizes energy efficiency with high thermal efficiency and selective heating to reduce waste heat.
Considerations: the ECO 11 is best suited for smaller homes or showers and sinks with modest simultaneous demand. It is not ideal for very high flow requirements in large baths when multiple fixtures demand hot water at once. The self-modulating system reduces energy use but requires careful sizing based on inlet water temperature and climate. The 99% thermal efficiency claim targets energy-conscious homeowners seeking space-saving solutions.
Rheem RTEX-24 — 24kW, High-Flow Electric Tankless
The Rheem RTEX-24 model targets higher flow applications with a 24kW, 240V configuration. It requires three 40-amp double-pole breakers and a robust electrical service (200 A recommended). The unit offers continuous hot water with attention to model-specific performance based on geographic conditions. The ON/OFF dial paired with a digital temperature display allows increment adjustments from 80-140 degrees Fahrenheit, facilitating adaptable performance for bathtubs and adjacent fixtures.
Considerations: ensure your electrical panel and service entry can support the higher load and that there is ample space for wiring and ventilation. Temperature stability depends on incoming water temperature and heater sizing; for a bathtub, you may need to balance flow rate with desired temperature. Professional installation is often advised due to wiring complexity and breaker requirements.
Under-Sink 110V Tankless Water Heater — 3000W
This compact 110V, 3000W under-sink heater is designed for point-of-use applications. It features an LED display and a range of protections, including water-electricity isolation and dry-heat protection. It can raise water by specific temperatures at low GPM, often suitable for sinks or occasional bath components rather than full-bath flow. It’s energy-conscious due to rapid response and efficient heat transfer, supporting instant hot water where a full bathroom circuit is impractical.
Considerations: this unit is not ideal for showering or high-flow bathtub use due to its lower GPM rating. It works best as a supplementary heater for sinks, basins, or as part of a multi-point system where one heater handles a dedicated fixture while another handles the tub area. Safety features help protect against overheating and leakage, which is critical in compact installations.
ECOTINYMACH 110V Tankless — Convertible Temperature Scale
The ECOTINYMACH 110V model emphasizes a compact footprint and a convenient Fahrenheit/Celsius switch. While primarily designed for under-sink use, its easy conversion between scales aids installation in homes with varied temperature labeling preferences. The unit targets quick setup and straightforward operation, making it a popular option for single-point use where space constraints exist.
Considerations: verify electrical supply compatibility, as 110V installations typically offer limited GPM. The device is best used for small-volume demands rather than a full bathtub or multiple fixtures. Durability and protection features are essential for under-sink placements, especially in humid bathroom environments.
2025 GEN II Ranein 18kW Tankless — High Capacity
The 2025 GEN II Ranein model provides 18kW at 240V with up to 4.3 GPM, designed to support 2-3 fixtures with no preheating delay. It requires two dedicated 240V circuits, 2×40A breakers, and 2×8 AWG cables. The unit emphasizes a high level of thermal efficiency at 99%, a compact footprint (13.8″×3.1″×18.7″), and a 3/4″ NPT water connection. The integrated temperature display and control knob facilitate straightforward adjustments for consistent bathtub temperatures.
Considerations: ensure your electrical service can handle two 40A double-pole breakers and that you have adequate space for installation. Inlet water temperature and piping length influence actual gallons per minute and temperature rise. The unit’s compact size can free up wall space, which is beneficial for bathroom remodels or tight utility closets. Proper sizing is essential to meet bath-time demand without excessive cycling.
Buying Guide: Key Purchase Considerations for Bath-Ready Electric Tankless Heaters
- Flow rate needs: For bathtub use, aim for at least 3-4 GPM when running hot water simultaneously with a sink or shower. Higher GPM models provide more headroom for busy households.
- Electrical requirements: Most 18kW units require two parallel 240V circuits (two 40A breakers) and 8 AWG wiring; smaller units may need 60A or similar. Verify service capacity and panel space before buying.
- Inlet water temperature: Cool inlet temperatures decrease effective GPM. In colder climates, you may need a higher-w wattage model or staged installations to maintain comfort at the tub.
- Technology and efficiency: Self-modulating or demand-based control helps minimize energy use. Look for models with copper immersion elements and ETL or equivalent certifications for safety.
- Size and installation: Compact, wall-mounted units save space in bathrooms and utility rooms. Consider the distance to fixtures and available venting or clearance around the unit.
- Maintenance and serviceability: Field-serviceable elements and easy access can reduce downtime. Ensure you can access the unit for periodic checks or replacements elegantly.
- Safety features: Leakage protection, dry-heat protection, and thermal cutoffs contribute to safer operation in humid bathrooms and under-sink areas.
- Warranty and support: Check manufacturer warranties and local service availability if you need professional installation or parts replacement.
- Multi-point compatibility: If you plan to run multiple fixtures, choose a model with proven performance at higher GPM and confirm compatibility with your existing plumbing layout.
In sum, selecting the best electric tankless heater for a bathtub involves balancing GPM capacity, electrical readiness, and installation space. The models highlighted above offer a range of capacities and form factors to suit diverse homes. For most bath-centered setups, targeting 3-4 GPM with two 40A circuits provides a reliable baseline, while compact designs help with tight bathrooms and closets. Always consult a licensed electrician to verify circuit requirements and safe installation.