10 Best high efficiency tankless electric hot water heaters 2025 in the United States

The Stiebel Eltron Tempra 29 Trend is a standout in the category of high-efficiency tankless electric hot water heaters, perfect for homeowners seeking an endless supply of hot water. Its continuous flow feature ensures that hot showers are never interrupted, which is a major plus for families or anyone who frequently uses hot water. With a power output of 28.8 kW, it quickly heats water between temperatures of 68°F and 140°F, catering well to varying needs.

One of its notable strengths is energy efficiency. This model is designed to save energy with its auto modulation feature, which adjusts the power usage according to demand, making it eco-friendly. Additionally, the compact size—16.63 inches wide and 14.5 inches high—allows for easy installation in tight spaces without the need for venting, which is a great space saver for modern homes.

The silent operation is another major advantage, as it operates quietly while in use, making it ideal for homes where noise is a concern. The digital temperature display is user-friendly and easy to read, adding to the convenience. The Tempra 29 Trend requires a substantial electric service of at least 200 A, which may not be feasible for all homes without an electrical upgrade. Although the warranties offered are generous—7 years for leakage and 3 years for parts—some users might find it a bit pricey compared to traditional water heaters, especially if they have lower hot water demands.

The Rheem 18kW 240V Tankless Electric Water Heater is a high-efficiency water heating solution with several notable strengths. Featuring an external digital thermostatic control with an LED display, it allows precise temperature management with a +/- 1 degree accuracy. This level of control is beneficial for maintaining consistent water temperature. The self-modulation feature is another significant advantage, as it adjusts power usage based on hot water demand, enhancing energy efficiency and potentially lowering electricity costs.

With a flow rate of up to 4.4 gallons per minute (GPM), it can support multiple fixtures simultaneously, making it ideal for medium-sized households. The durable copper immersion heating elements are robust and field-serviceable, ensuring longevity and ease of maintenance. Additionally, the unit's design includes bottom 3/4 inch NPT water connections and threaded connections, simplifying installation and replacement processes.

However, the product does have some limitations. The power requirement of 18,000 watts at 240 volts may be high for some homes, necessitating a professional electrical assessment before installation. Additionally, the product dimensions, while relatively compact, might still require adequate space for installation. The Rheem 18kW 240V model stands out as an efficient and reliable option for those seeking a tankless electric water heater with modern features and strong performance.

The Rheem RTEX-24 24kW 240V Electric Tankless Water Heater offers an impressive flow rate of up to 5.9 gallons per minute (GPM), which is quite strong for most household needs. Its self-modulating power control ensures efficient energy use by adjusting power based on hot water demand, contributing to its notable 99.8% energy efficiency.

The adjustable digital temperature display with an ON/OFF dial control makes it user-friendly, allowing for precise temperature adjustments and easy monitoring. Installation should be straightforward with its compact size (17.63”W x 18.25”H x 3.5”D) and wall-mount design, although professional installation is recommended due to the 24kW power requirement and 240V voltage. The unit's weight of 17.8 pounds is manageable for most installation scenarios.

Durability is supported by the stainless steel finish and robust build. The maximum water pressure of 150 PSI should be checked against your home’s water pressure to ensure compatibility. This heater is well-suited for homeowners looking for an efficient, high-performing solution to provide continuous hot water on demand.