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

The Stiebel Eltron Tempra 36 Plus is a high-powered tankless electric water heater designed to deliver continuous hot water on demand. It operates at 27,000 watts with a maximum flow rate of 1.5 gallons per minute, which is suitable for smaller households or point-of-use setups but might be limiting if you need simultaneous hot water at multiple fixtures. Its advanced flow control and self-modulation technology help save energy by adjusting power use based on demand, making it a strong choice if you're looking to reduce utility bills.

The digital LED display allows for precise temperature control, which adds convenience and helps maintain consistent water temperature. Installation is straightforward with a floor mounting method, and the unit is relatively compact at about 17 by 14.5 inches, so it won’t take up much space. However, it requires a 208-volt power supply, which might need electrical upgrades in some homes. The product is well-reviewed for reliability and efficiency.

If you want an energy-efficient electric tankless heater for a smaller capacity setting and don’t mind the electrical requirements, the Tempra 36 Plus represents a solid, dependable option.

The Stiebel Eltron Tempra 29 Plus is a powerful, high-efficiency tankless electric water heater designed to provide continuous hot water on demand. It delivers up to 3 gallons per minute, which is suitable for a household with moderate hot water needs, like running one or two showers plus a sink at the same time. Its compact size (about 17 by 15 inches) helps save space and the sleek design means no venting is required, making installation flexible for many homes.

The unit has a strong 28.8 kW power output, meaning it can heat water quickly with a notable temperature rise, which is great if you live in colder climates and need a consistent hot water supply. An LED display and two temperature memory presets make it easy to set and save your preferred water temperatures. On the energy side, it’s very efficient, so it won’t waste electricity heating water when you don’t need it. However, this heater requires a substantial electrical setup: a dedicated 240-volt or 208-volt hard-wired connection, 3 separate 40-amp breakers, and at least a 200-amp main service panel. This means you might need professional electrical upgrades, which can add to installation cost and complexity.

The unit is relatively lightweight at 24 pounds and mounts on the wall, freeing up floor space. If you have a large household or very high hot water demands, you might find the 3 GPM flow limiting, but for many, it balances power, efficiency, and convenience effectively.

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.