Best Electric Tankless Water Heater for Bathtub
When choosing an electric tankless water heater for a bathtub, homeowners want reliable hot water on demand, compact installation, and energy efficiency. The following selections are among the best options for delivering steady baths without a bulky tank. Each product below is evaluated for GPM flow, installation requirements, and overall performance to support a comfortable bathtub experience.
| Product | Brand | Approximate Flow (GPM) | Notes |
|---|---|---|---|
| 18kW Tankless Water Heater Electric, ORBEK Instant On Demand Hot Water | Orbek | Up to 4.17 | Supports 2–3 fixtures simultaneously |
| Rheem 18kW 240V Tankless Electric Water Heater, Gray | Rheem | Up to 4.4 | Self-modulating, LED thermostat |
| 14kW Tankless Water Heater Electric, ORBEK 240V | Orbek | Up to 3.38 | LED digital display |
| EcoSmart ECO 11 Electric Tankless Water Heater | EcoSmart | Up to 1–2 | Self-modulating, compact design |
| Rheem RTEX-24 24kW 240V Electric Tankless Water Heater | Rheem | Varies with power | Multiple 40A circuits required |
The selection below focuses on units that balance flow capacity with efficient performance, ease of installation, and suitability for a bathtub setup. Each product section provides practical details to help you compare installation needs, energy use, and on-demand hot water reliability.
Orbek 18kW Instant On-Demand Water Heater
This 18kW electric tankless unit from Orbek is designed for indoor installation and can supply up to 4.17 GPM, making it suitable for hot water at multiple points of use. It requires two 240V/40A two-pole breakers, two sets of 8 AWG wiring, and 3/4″ NPT water connections. The heater uses water-electrical separation to minimize scale and corrosion, delivering hot water in seconds and potentially reducing energy costs compared with traditional tanks.
For bathtub use, this model can provide reliable on-demand hot water to one or two outlets simultaneously, which is helpful for filling a tub while nearby fixtures receive hot water. The unit’s efficient design and rapid response time support comfortable bath experiences, though higher flow scenarios may approach its limit depending on inlet water temperature.
Rheem 18kW 240V Tankless Electric Water Heater
Rheem’s 18kW tankless model features external digital thermostatic control with an LED display and self-modulation to adjust power according to demand. It uses durable copper immersion heating elements and is field serviceable. With a flow rate potential up to 4.4 GPM, it is well-suited for a bathtub plus another outlet in a typical American home. The self-modulating design helps maintain a stable output while varying water temperature.
For bathtub installations, consider the electrical service capacity and available panel space. This Rheem unit provides reliable on-demand hot water, but ensure your electrical infrastructure can support the unit’s required power draws without impacting other heavy loads in the home.
Orbek 14kW Electric Tankless Water Heater
This 14kW Orbek model provides up to 3.38 GPM for two to three points of use, including a bathtub. It includes a LED digital display for temperature monitoring and requires a 240V/60A two-pole breaker, one set of 6 AWG wires, and 1/2″ NPT water connections. The design emphasizes fast on-demand hot water and energy efficiency through water-electrical separation.
In a tub-centric setup, this unit offers a compact option when electrical capacity is limited, while still delivering consistent hot water for moderate bath flows. If you frequently run hot water at higher flow, pairing with other demand-reducing strategies or choosing a higher-capacity model may be worth considering.
EcoSmart ECO 11 Electric Tankless Water Heater
EcoSmart’s ECO 11 is a compact, self-modulating electric tankless water heater rated at 13 kW. It typically serves 1–2 fixtures with stable performance, using temperature-controlled flow to maintain efficiency. Its small footprint—about 11.5 by 8 by 3.75 inches—makes it ideal for tight spaces or point-of-use installation near a bathtub.
For bathtub applications, this unit can provide reliable hot water at moderate flow levels and is highly space-efficient. The self-modulating technology reduces energy use by heating only when needed, which is advantageous for households prioritizing energy savings. Consider limitations in multi-outlet baths or scenarios requiring higher flow.
Rheem RTEX-24 24kW Tankless Water Heater
The Rheem RTEX-24 is a higher-capacity unit designed for larger homes or greater simultaneous hot water needs. It requires three 40A double-pole breakers and is intended for use with a 200-amp service. It features an adjustable dial and digital temperature display for precise water temperature control, with performance influenced by incoming water temperature and elevation.
In bathtub scenarios, the RTEX-24 can deliver robust hot water for larger baths or when other fixtures demand hot water at the same time. Installation demands a substantial electrical footprint and adequate space in the breaker panel. This model is best suited for homes with ample electrical service and a need for strong flow at modest temperatures rises.
Under-Sink 110V Tankless Water Heater
This 110V under-sink unit provides 3000W of instant hot water with an integrated digital display. It is a compact, plug-in option intended for point-of-use applications where a full-house system isn’t required. It can raise water by roughly 82°F at 0.3 GPM or to 131°F at 0.5 GPM, depending on flow and incoming water temperature.
For bathtub use, this model is best suited for small, localized hot water needs rather than full-bathflow. It is not ideal for showers or high-flow baths, but it can be a convenient adjunct for supplementary hot water near the tub, especially when space or electrical load is a concern.
ECOTINYMACH 110V Tankless Water Heater
ECOTINYMACH’s 110V unit offers 3000W of instant hot water with a compact under-sink footprint. It emphasizes easy installability and flexible temperature scale options, allowing users to monitor temperature in Fahrenheit or Celsius. The unit’s efficiency and straightforward setup appeal to spaces where a dedicated 240V line is unavailable.
While suitable for point-of-use needs near the bathtub, its maximum flow is lower than larger 240V models. Users seeking consistent, higher-volume hot water for a full tub bath may prefer a higher-capacity heater, but this model provides a practical, space-conscious option for modest bath usage.
2025 GEN II Ranein Tankless Water Heater
Ranein’s 18kW, 240V model delivers up to 4.3 GPM and includes a temperature display with a control knob for precise adjustment. It requires two dedicated 240V circuits (two 40A breakers) and two 8 AWG cables, plus a 3/4″ NPT water connection. The unit emphasizes high thermal efficiency and a compact size that can fit in tight spaces while delivering consistent on-demand hot water.
For bathtub use, the Ranein GEN II is a strong option for households needing reliable hot water at moderate to high flow. Its efficiency and rapid delivery make it suitable for baths that demand quick water warming, subject to adequate electrical capacity and proper installation.
Buying Guide: Key Purchase Considerations for Bathtub Use
- Flow rate needs: For baths, aim for units in the 2–4 GPM range when filling a tub while operating other fixtures.
- Electrical service: Many 18 kW units require two dedicated 240V circuits and robust service capacity; verify panel space and wiring.
- Incoming water temperature: Warmer inlet water reduces required heating power and improves efficiency; high-lift scenarios may demand higher-capacity models.
- Space and installation: Tankless heaters are compact, but mounting location and clearances matter for safe operation and ease of maintenance.
- Durability and serviceability: Look for units with copper heating elements, field serviceability, and clear temperature control.
- Self-modulating technology: This feature helps regulate power usage and maintain stable output as hot water demand changes.
- Point-of-use vs whole-house: Point-of-use units near the tub minimize heat loss, while whole-house units can support multiple fixtures but require larger electrical capacity.