10 Best Tankless Hot Water Heaters 2026 in the United States

The Rheem 18kW 240V Tankless Electric Water Heater in Gray offers several appealing features for those in need of a compact and efficient water heating solution. The primary advantages of this model include its advanced self-modulation technology, which helps adjust power based on the hot water demand, ensuring energy efficiency and cost savings. Additionally, it boasts a flow rate of up to 4.4 GPM, which is suitable for small to medium households, providing enough hot water for multiple uses simultaneously.

The external digital thermostatic control with an LED display allows for precise temperature adjustments, enhancing user convenience and comfort. The heater is also equipped with durable copper immersion heating elements, which are field serviceable, making it easier to maintain and extend its lifespan. Installation is straightforward due to the bottom 3/4 inch NPT water connections and threaded design, allowing for easy replacement if necessary.

However, there are some drawbacks to consider. As an electric heater, it may not be as efficient or cost-effective in areas with high electricity rates compared to gas-powered models. Additionally, the temperature rise might be limited in very cold climates, potentially affecting the heater's performance. The size and installation process, while simple, may still require professional assistance for those unfamiliar with electrical systems. Lastly, it's essential to review the warranty and support options from Rheem to ensure long-term reliability. The Rheem 18kW 240V Tankless Electric Water Heater is a strong choice for individuals seeking an energy-efficient, easy-to-use, and maintain water heating solution within the limitations of an electric-powered system.

The Rheem RTEX-24 Electric Tankless Water Heater is a solid choice for those seeking an efficient and high-capacity water heating solution. One of its major strengths is its impressive flow rate of up to 5.9 gallons per minute (GPM), which is suitable for serving multiple fixtures simultaneously. Additionally, its 99.8% energy efficiency rating makes it an economical option, as it minimizes energy waste and reduces utility bills.

The electric fuel type ensures ease of installation without the need for gas lines, making it a convenient option for many users. Its compact size (17.63"W x 18.25"H x 3.5"D) and wall-mount capability further enhance its suitability for smaller spaces or areas where floor space is at a premium. The product also boasts a user-friendly digital temperature display and self-modulating power control, which contribute to maintaining consistent and continuous hot water supply on demand.

However, there are some drawbacks to consider. The maximum flow rate may not be sufficient for larger households with high hot water demands during peak usage times. In summary, the Rheem RTEX-24 is an excellent option for small to medium-sized households or professional use, offering high efficiency, ease of installation, and reliable performance within its capacity limits.

The Rinnai RE180eP is a propane-powered outdoor tankless water heater designed to deliver hot water on demand without storing it. It offers a strong maximum flow rate of up to 8.5 gallons per minute, which is suitable for running multiple fixtures like showers and faucets at the same time in medium to larger households. Being non-condensing, it’s simpler in design but slightly less energy-efficient compared to condensing models, though it still includes features like an LED display to help with maintenance and efficiency reminders.

This model’s compact size, roughly like a small suitcase, makes it easier to install in limited outdoor spaces, but professional installation is recommended to ensure safety and proper setup. It provides a solid temperature rise capacity to meet typical household needs, though exact temperature increase depends on your incoming water temperature and region. The heater comes with a layered warranty—15 years on the heat exchanger, 5 years on labor, and 1 year on parts—to support long-term reliability.

A convenient option is the ability to add WiFi control via an additional module, allowing remote monitoring. This Rinnai unit is a strong choice for those wanting a reliable, high-flow propane outdoor tankless heater with smart features and solid support, while noting it may not be the highest in energy efficiency compared to condensing models.