10 Best Tankless Instant Water Heaters 2025 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 Stiebel Eltron Tempra 29 Trend tankless water heater is a robust and efficient option for those needing continuous hot water. With a 28.8kW power output, it ensures a consistent flow of hot water, making it suitable for whole-house use. The unit boasts strong energy efficiency, thanks to its auto-modulation feature, which adjusts the energy consumption based on demand.

Its compact design saves space and does not require venting, making installation simpler and more versatile. Additionally, the silent operation and easy-to-read digital temperature display add to its user-friendly experience. The solid copper heating system ensures durability and reliability. However, it requires a significant electrical service (200 A), which may necessitate electrical upgrades for some homes.

The warranties provided (7 years for leakage and 3 years for parts) offer added peace of mind. Even though there might be an initial investment and potential need for electrical upgrades, the Tempra 29 Trend is a worthy choice for households seeking efficient, eco-friendly, and reliable hot water on demand.

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.