10 Best Tankless Hot Water Heaters 2025 in the United States

The Rinnai RX199iN is a powerful tankless water heater that stands out for its impressive flow rate of up to 11.1 gallons per minute, making it suitable for homes with multiple fixtures needing hot water simultaneously. It's designed to operate on either natural gas or propane, giving you flexibility depending on your fuel source. The energy efficiency is top-notch, boasting a UEF rating of .98, which means it uses energy very effectively, potentially saving you on utility bills.

One of the great features is its compact size, comparable to that of a small suitcase, making it easier to fit into various spaces. The Smart Sense gas control system adds convenience, allowing for easier operation. However, the installation of this unit is recommended to be done by a professional. While this ensures safety and proper functionality, it could increase your expenses if you don’t have a technician readily available.

While its high efficiency is a significant advantage, it may not be the best choice for all water temperature needs depending on your region’s groundwater temperature. Additional considerations include the need for the RX-OVC vent cap for outdoor installation, which adds to the installation complexity and cost. Also, the Controlr module for WiFi control is sold separately, which might be a drawback for those looking for smart home integration right out of the box. If you are looking for a tankless heater that offers high performance and efficiency, the Rinnai RX199iN is a strong contender. Just ensure you’re prepared to handle the installation requirements and additional features you may want to consider.

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 RTG-84XLN-3 is a high-efficiency, non-condensing outdoor tankless natural gas water heater designed to provide continuous hot water. With a maximum flow rate of 8.4 gallons per minute, this unit can supply enough hot water for multiple applications simultaneously, such as showers and dishwashers, making it ideal for larger households. It is also designed to save on energy costs by only running when needed, and its water-saving setting can save up to 1,100 gallons of water per year. Additionally, its hot-start programming helps avoid cold-water bursts by keeping the heater in a ready state.

The Rheem RTG-84XLN-3 is 19% smaller and 22% lighter than previous models, which simplifies installation and saves space. It has a maximum temperature of 140 degrees Fahrenheit and is certified for high efficiency by GAMA. The unit is designed for outdoor installation and mounts on a wall, making it convenient for homeowners who want to save indoor space. The product dimensions are 13.5 inches by 20.75 inches, and it weighs 39.2 pounds.

Some potential drawbacks include its reliance on natural gas, which may not be suitable for all homes, and the need for professional installation. Additionally, while the unit is efficient, it may not perform as well in extremely cold climates where higher temperature rises are needed. However, for most households looking for a reliable and space-saving tankless water heater, the Rheem RTG-84XLN-3 appears to be a strong contender.