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

The Rheem 18kW 240V Tankless Electric Water Heater offers a solid performance for providing on-demand hot water. One of its standout features is the external digital thermostatic control with an LED display that allows you to precisely adjust the temperature to your liking, with a high accuracy of +/- 1 degree. The unit’s self-modulating technology is highly efficient as it adjusts the power usage to meet the hot water demand, which can help reduce energy consumption.

With a flow rate of up to 4.4 gallons per minute (GPM), this heater is capable of handling the hot water needs of a small household or apartment with ease. The use of durable copper immersion heating elements ensures a longer lifespan and easier maintenance since they are field serviceable. Installation is made simple with the 3/4 inch NPT water connections and threaded design, ensuring a straightforward setup and easy replacement if needed.

Potential buyers should be aware that the maximum power rating of 18,000 watts requires a substantial electrical setup, which might not be suitable for all homes without electrical upgrades. Additionally, while the unit is energy-efficient due to its self-modulation, its effectiveness in extremely cold climates may be limited as the temperature rise it offers might not be sufficient in such conditions. The compact dimensions of 14.5 inches in width and 18.25 inches in height make it easy to fit in tight spaces, adding convenience to its installation. This water heater is an excellent choice for those looking for an efficient and easy-to-install unit for a small to medium-sized household, provided that the electrical requirements can be met.

The Stiebel Eltron Tempra 20 Plus is a well-rounded electric tankless water heater designed to provide continuous hot water on demand. One of its standout features is the Advanced Flow Control technology, which ensures a consistent temperature by automatically adjusting the water flow if demand exceeds capacity. This means you can enjoy uninterrupted hot showers, a major plus for households with high hot water usage.

With a power rating of 19.2kW and the ability to produce water temperatures ranging from 68° to 140°F, it is powerful enough for most residential needs. The unit is also quite energy-efficient, utilizing auto-modulation and electronic water flow control to reduce energy consumption. Its compact design, measuring just 16.63 inches wide and 14.5 inches high, makes it easy to install in tight spaces without the need for venting.

Additionally, it comes with a clear digital temperature display and preset memory buttons for ease of use. Safety is also a priority, with built-in features to prevent overheating and a solid copper heating system for durability. However, the unit requires a minimum recommended electric service of 125 A, which could necessitate an electrical upgrade in some homes. Despite a higher upfront cost compared to traditional water heaters, the long-term energy savings and the convenience of endless hot water can justify the investment for many users. The inclusion of a 7-year leakage warranty and a 3-year parts warranty adds peace of mind. This heater is ideal for eco-conscious homeowners looking for a reliable and efficient hot water solution that saves space and energy.

The Rheem RTEX-24 Electric Tankless Water Heater is a robust option for providing continuous hot water on demand. With a powerful 24kW rating, it boasts an impressive flow rate of up to 5.9 gallons per minute (GPM), making it suitable for medium to large households. The self-modulating power control ensures energy efficiency, adjusting power usage based on hot water demand, which contributes to its high 99.8% energy efficiency rating. This can potentially save on energy costs over time.

The digital temperature display and ON/OFF dial control allow for precise temperature adjustments, enhancing user convenience and safety. The unit's compact size (17.63”W x 18.25”H) and wall-mount installation make it easy to fit in various spaces without requiring a large footprint. However, installation should ideally be handled by a professional to ensure it meets safety standards and operates correctly.

One drawback is that it requires a 240V electrical connection, which might not be readily available in all homes and could necessitate electrical upgrades. Additionally, while its maximum operating pressure is suitable for most residential needs, the heater's performance might diminish in very cold climates where incoming water is much colder. The Rheem RTEX-24 is a highly efficient and powerful tankless water heater, ideal for households looking for a steady supply of hot water, provided the electrical setup supports its requirements.