10 Best Electric Tankless Hot Water Heater 2025 in the United States

The Rheem 18kW 240V Tankless Electric Water Heater is designed to offer an on-demand hot water solution for homeowners looking to save space and energy. With a flow rate of up to 4.4 gallons per minute (GPM), it can efficiently supply hot water for multiple outlets at once, making it suitable for medium-sized households or apartments. One standout feature is its external digital thermostatic control with a precise +/- 1 degree accuracy, allowing users to easily set their desired water temperature.

The self-modulation technology adjusts the power based on your hot water needs, optimizing energy use and maintaining efficiency, which is an impressive 99.8%. This means you can enjoy hot water without worrying too much about energy bills.

Installation is relatively straightforward with its wall-mount design and 3/4 inch NPT connections which simplify the setup process. The durable copper heating elements are also field-serviceable, contributing to the unit’s longevity. There are a few drawbacks to consider. The unit requires a 240V power supply and an adequate electrical setup, which might necessitate professional installation if your home isn’t equipped. It may not be powerful enough for larger households or homes with high demand for simultaneous hot water use.

The Stiebel Eltron Tempra 36 Trend is a powerful electric tankless water heater designed to provide endless hot water on demand, making it a strong choice for whole-house use. With a high wattage of 27,000 watts and operating at 240 volts, it can deliver water temperatures between 68°F and 140°F, which means it can handle significant temperature rises efficiently. Its compact size (about 16.6 by 14.5 inches) and wall-mount design help save space, and since it doesn't require venting, installation can be simpler than gas heaters.

One standout feature is its energy-saving auto-modulation, which adjusts power based on demand to reduce wasted energy. The unit operates silently and includes an easy-to-read LED temperature display, adding to user convenience. However, it requires a substantial electrical service—recommended minimum of 300 amps—which might mean electrical upgrades in some homes, making installation more costly and complicated. The heater comes with a solid 7-year warranty against leaks and a 3-year parts warranty, reflecting confidence in its durability.

While it’s highly energy-efficient and well-suited for larger households needing continuous hot water, the heavy electrical requirement and potentially higher upfront installation costs might be drawbacks for some users. If your home’s electrical system can support it, this model offers reliable performance and energy savings in a compact, quiet package.

The Rheem RTEX-24 is a solid choice for anyone looking for an electric tankless water heater, particularly for residential use. One of its key strengths is its impressive flow rate of up to 5.9 gallons per minute, making it suitable for medium to large households where multiple hot water outlets may be used simultaneously. Its self-modulating power control ensures that the heater adjusts energy use based on demand, which can help in energy savings. With an energy efficiency rating of 99.8%, this unit can significantly reduce your utility bills compared to traditional tank heaters.

The adjustable digital temperature display is user-friendly, allowing for easy temperature adjustments to find that just-right warmth. The compact design, with dimensions that allow for wall mounting, can save space in smaller homes.

There are a few considerations to keep in mind. The installation might require a professional, especially if you’re not handy, as it involves electrical connections that must be done correctly for safety. Additionally, while the heater’s specifications are strong, it may struggle if you have high hot water demands at multiple points at once, depending on the temperature rise needed and your incoming water temperature. Lastly, Rheem provides a warranty, but it's always good to check the specifics to ensure you’re covered in case of any manufacturing defects. If you’re seeking a reliable and efficient hot water heater for your home, the Rheem RTEX-24 is certainly worth considering.