10 Best On Demand Water Heaters 2026 in the United States

The Rinnai RXP199iN Condensing Smart Sense Tankless Water Heater stands out with its impressive flow rate of up to 11.1 gallons per minute (GPM), which can support multiple fixtures simultaneously. This makes it a great choice for larger households or those with high hot water demand. The energy efficiency is excellent, boasting a Uniform Energy Factor (UEF) of 0.98, meaning it effectively converts fuel into usable heat, leading to potential savings on energy bills.

The device operates on both natural gas and propane, offering flexibility depending on your fuel availability or preference. Its compact size, similar to a small suitcase, allows for versatile installation either indoors or outdoors, thanks to the Versa Vent system. Additionally, the Smart-Circ Intelligent Recirculation feature learns your hot water usage patterns to optimize performance and efficiency, though it may take some time to adjust correctly to your routine.

The unit is fairly lightweight at 58 pounds, but professional installation is strongly recommended to ensure proper setup and operation. A potential downside is the additional cost for the Control-R module if you want WiFi connectivity for remote control and monitoring. Also, while the temperature rise and maximum output of 199,000 BTU are suitable for most homes, it's important to ensure it's compatible with your specific requirements. This water heater is highly efficient and powerful, suitable for households needing a reliable and flexible hot water solution.

The Rinnai RXP160iN Condensing Smart Sense Tankless Water Heater stands out in the on-demand water heater category for several reasons. It offers a high flow rate of up to 9 gallons per minute (GPM), which means it can handle up to six fixtures simultaneously – making it suitable for larger households or homes with high hot water demands.

The energy efficiency rating is impressive with a Uniform Energy Factor (UEF) of 0.97, reflecting excellent energy savings and reduced operating costs over time. Additionally, it supports both natural gas and propane fuel types, providing flexibility based on the available fuel source in your home.

Its compact size, comparable to a small suitcase, and the ability to install it both indoors and outdoors, thanks to the versatile venting options, add to its adaptability and space-saving benefits. The Smart-Circ Intelligent Recirculation feature is a notable advantage, as it learns your hot water usage patterns to optimize efficiency and convenience. The Rinnai RXP160iN also comes with a Quick Flush feature for easy maintenance, although the WiFi control module is not included.

Despite these strengths, professional installation is recommended, which could add to the initial costs. Furthermore, while the maximum temperature of 140 degrees Fahrenheit is standard, some users might prefer higher temperature settings, though this is generally sufficient for most home applications. This water heater is a reliable choice for those needing consistent and efficient hot water supply.

The Rheem 18kW Tankless Electric Water Heater is a solid choice for homeowners looking for an efficient, on-demand hot water solution. It uses electricity, which means no gas hookups or emissions, and offers a high energy efficiency of 99.8%, helping to reduce utility bills. The flow rate maxes out at 4.4 gallons per minute, suitable for small to medium households but might struggle if you need multiple showers or appliances running at once.

Installation is fairly simple with bottom water connections and wall mounting, but keep in mind it requires a 240V power supply and a 75-amp electrical circuit, which may need professional setup if your home isn’t already wired for this. The temperature control is precise thanks to the external digital thermostat with LED display, letting you adjust water temperature within 1-degree accuracy up to 140°F. Durable copper heating elements are field serviceable, adding to longevity and ease of maintenance. The unit is compact, saving space compared to traditional tanks.

Rheem typically offers reliable support for their products. If you want a dependable, energy-efficient electric tankless heater for a household with moderate hot water needs, this model is a practical pick. However, larger homes or those with heavy simultaneous hot water use might need a model with higher flow capacity or multiple units.