10 Best Tankless Instant Water Heaters 2026 in the United States

The Rinnai RXP199iN Condensing Smart Sense Tankless Water Heater is a versatile option that can be installed indoors or outdoors. The ability to use either natural gas or propane makes it adaptable for different homes. With a flow rate of up to 11.1 gallons per minute, it can comfortably serve multiple fixtures simultaneously, ensuring you never run out of hot water. Its high energy efficiency factor of UEF .98 is commendable, meaning it uses energy very effectively and could help reduce utility bills over time.

The Smart-Circ Intelligent Recirculation feature is a notable advantage as it learns your usage patterns to optimize hot water availability and efficiency. Additionally, its compact size (19”W x 31”H) helps save space, making it an excellent choice for smaller homes or apartments. Professional installation is strongly recommended, which can add to the upfront cost. While it has a modern design and the potential for WiFi connectivity via the Control-R module, this add-on is not included and must be purchased separately.

The 199,000 BTU heat output ensures a significant temperature rise, capable of handling high-demand scenarios. Warranty and support are accessible through Rinnai’s website.

The Rheem RTEX-24 is a 24kW electric tankless water heater designed to deliver continuous hot water for an entire home. It offers a maximum flow rate of about 5.9 gallons per minute, which is generally enough for multiple outlets but might struggle with simultaneous high-demand uses in larger households. The unit heats water efficiently with a digital temperature control allowing precise adjustments from 80 to 140°F, helping you get comfortable water temperature without waste.

Its energy efficiency is impressive, rated at 99.8%, which means most of the electricity is converted to hot water, saving on energy costs over time. Being electric, it requires a significant electrical setup—three double-pole 40 amp breakers and a 200 amp household service are recommended, so make sure your home’s electrical panel can handle this before purchase. The heater is compact and wall-mounted, measuring about 17.6 by 18.25 inches and only 3.5 inches deep, which is great for saving space and easy installation where venting isn't needed.

Rheem is a reputable brand and the unit comes with a helpful LED display for temperature control, though the electrical requirements may mean additional installation costs if your home’s wiring needs upgrading. Also, keep in mind that the temperature rise and flow rate depend on your local groundwater temperature, so performance can vary by location. This model is ideal for homeowners looking for an energy-efficient, space-saving electric tankless water heater who have adequate electrical capacity and moderate hot water needs.

The Rheem 18kW 240V Tankless Electric Water Heater offers several appealing features for those seeking a reliable tankless water heater. It boasts a flow rate of up to 4.4 gallons per minute (GPM), which is suitable for small to medium households. The external digital thermostatic control with an LED display ensures precise temperature adjustments within 1-degree accuracy, allowing users to set their desired water temperature easily.

The advanced self-modulation feature enables the heater to adjust power based on hot water demand, enhancing energy efficiency and potentially lowering energy bills. The durable copper immersion heating elements are field-serviceable, making maintenance more straightforward. Installation is simplified with its bottom 3/4 inch NPT water connections, and it's threaded for easy replacement.

Its wattage of 18000 watts means it may require an electrical system upgrade for some households. Its compact dimensions (14.5"W x 18.25"H) make it a good fit for tight spaces, but users should ensure they have adequate installation space. The gray color may blend easily with most decor. This model is best suited for those who prioritize precise temperature control, easy installation, and energy efficiency in their tankless water heater.