10 Best Indoor Gas Tankless Water Heater 2025 in the United States

The Rinnai RXP199iN Condensing Smart Sense Tankless Water Heater is a solid choice for those looking for an efficient indoor gas water heater. With a flow rate of up to 11.1 gallons per minute (GPM), it can easily supply hot water to several fixtures simultaneously, making it ideal for larger households. Its high BTU rating of 199,000 means it can heat water quickly, ensuring you never run out of hot water when you need it most.

One of the standout features of this model is its impressive energy efficiency, with a UEF rating of .98. This means it can help you save on energy bills over time, which is a significant advantage for environmentally conscious consumers. The Smart-Circ technology is another highlight; it learns your hot water usage patterns to optimize recirculation, ensuring you get hot water faster without wasting energy.

There are some things to keep in mind. The installation process is recommended to be done by a professional, which could add to your overall costs if you're planning to buy this unit. Its compact size is a plus, but you'll still need adequate wall space for installation. Additionally, while it supports WiFi connectivity through the Control-R module, this feature is sold separately, which could be an extra expense for those looking for smart home integration.

The Ranein Natural Gas Tankless Water Heater offers a solid flow rate of up to 5.3 gallons per minute (GPM), making it suitable for a household with 3-5 water outlets. With a BTU rating of 130,000, it provides a strong heating capacity, ensuring you have instant hot water without the need to wait. This is particularly beneficial in colder climates where hot water on demand is essential.

The compact size (23.15"L x 14.17"W x 5.9"H) makes it easy to install in limited spaces, and the standard fittings contribute to a straightforward installation process. Additionally, the fans placed underneath help ensure safety by preventing smoke backflow and adjusting to external conditions for optimal combustion. However, it's important to note that this unit is not recommended for use in areas above 2,000 feet due to efficiency issues.

While the product has a reasonable energy efficiency, the 2-year warranty provides some assurance, but it is shorter compared to some competitors who offer longer warranties. With a positive customer rating of 4.3 out of 5 stars, users generally appreciate its performance and ease of use, although some might find the noise level from the fans slightly bothersome. If you seek an affordable, compact, and reliable indoor gas tankless water heater, the Ranein model RH13K-NG could be a good fit, provided you are within the recommended altitude range.

The Ranein Natural Gas Tankless Water Heater offers a solid performance with a heating capacity of 100,000 BTU and a maximum flow rate of 4.3 gallons per minute (GPM). This makes it suitable for providing continuous hot water to multiple points in a household, such as a bathroom, kitchen, and bar area. One of the standout features is the Four Seasons Function, which automatically adjusts the water temperature based on seasonal changes, and the Kitchen Function, which sets the default temperature to 100°F for kitchen use.

Additionally, the Bathtub Function allows for adjustable water output with reminders, enhancing convenience for various needs. Immediate hot water on demand eliminates the need for preheating, a significant advantage over traditional tank water heaters. The inclusion of the exhaust pipe in the kit saves additional costs and simplifies installation. The energy efficiency is bolstered by the oxygen-free copper water tank, which reduces heat loss and lowers energy consumption.

However, it's essential to adhere to local building and plumbing regulations and opt for professional installation. A notable limitation is that it is not recommended for use at elevations over 2,000 feet, which might restrict its applicability in high-altitude areas. The compact design, with dimensions of 18.89 inches in width and 8.85 inches in height, makes it suitable for homes with limited installation space. This tankless water heater is ideal for households needing efficient and continuous hot water but may not be suitable for high-altitude regions.