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

The Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane Tankless Water Heater is a strong contender for anyone looking to upgrade their home’s hot water system. With a flow rate of up to 11.1 gallons per minute (GPM), it can easily handle multiple fixtures simultaneously, making it suitable for larger households or those with high hot water demands. Its high BTU rating of 199,000 ensures quick heating, which is a significant advantage over traditional tank water heaters.

Energy efficiency is another highlight, boasting a UEF rating of .98, which means it consumes less energy compared to many alternatives. This not only translates to lower utility bills but also aligns well with environmentally conscious choices. The compact design, about the size of a small suitcase, allows for flexible installation in various spaces, whether indoors or outdoors, thanks to the Versa Vent feature.

However, there are some drawbacks to consider. The requirement for professional installation may add to the cost, particularly for those who are looking to save on installation fees by doing it themselves. Additionally, while the Smart Sense gas control system simplifies usage and efficiency, it doesn’t come with the compatible WiFi module by default, which may be a missed feature for tech-savvy users seeking remote management.

The Ranein Natural Gas Tankless Water Heater is designed for indoor use and offers a substantial flow rate of up to 7.4 GPM, making it suitable for medium to large households with 4-6 outlets. With a high heating capacity of 190,000 BTU, this unit ensures instant and continuous hot water without the need for preheating, which is a significant advantage over traditional tank heaters. The fans placed underneath enhance safety by preventing smoke backflow and ensuring full combustion with low noise levels and longer service life.

Its compact design (24.25”L x 15.08”W x 8.07”H) allows for easy installation in smaller spaces, and it uses standard fittings for convenience. Additionally, the product comes with a 2-year warranty, providing some peace of mind, although this is relatively short compared to some competitors who offer longer warranties. However, there are a few drawbacks. The unit is not recommended for use in areas above 2,000 feet altitude, which could limit its applicability.

Moreover, users in colder climates need to manually drain the unit if it's not used for a while to prevent damage, adding a bit of maintenance. Despite these minor issues, the Ranein Natural Gas Tankless Water Heater is a strong contender for households needing an efficient and reliable hot water solution.

The Rinnai RX180iN is a powerful and versatile indoor gas tankless water heater that can run on natural gas or propane. It delivers up to 10 gallons per minute, which means it can supply hot water to about six fixtures at the same time — a solid choice for medium to large homes. With a high BTU rating of 180,000, it quickly heats water to your desired temperature without delay. Its energy factor of 0.98 means it’s very efficient, helping to reduce your utility bills compared to older models.

The unit is fairly compact, about the size of a small suitcase, making it easier to fit in tight spaces. It also has flexible venting options and can be installed indoors or outdoors with the proper vent cap, adding to installation convenience. The interface is user-friendly, and it supports smart features like WiFi control through an optional module, allowing you to monitor and adjust settings remotely. However, this model is designed to be professionally installed, so DIY installation is not recommended. One thing to keep in mind is the 140°F maximum temperature, which is sufficient for most households but might be limiting if you need hotter water.

This Rinnai model represents a reliable, energy-efficient tankless heater with good flow capacity for everyday use, making it an excellent choice for those who appreciate modern features and flexible installation.