INSTANT HOT WATER FOR SMALL HOMES:This indoor natural gas tankless water heater delivers up to 3.6 GPM flow rate and 85,000 BTU heating capacity, providing endless hot water on demand for 2–3 fixtures simultaneously, ideal for small houses, cabins, and apartments. INTELLIGENT CONSTANT TEMPERATURE PLUS:Equipped with Intelligent Constant Temperature PLUS technology, this natural gas tankless water heater steplessly adjusts the air-fuel ratio to maintain stable water temperature within ±1℉, even when another water outlet is suddenly turned on, reducing temperature fluctuations and scalding risk. 4-STAGE ENERGY-SAVING COMBUSTION TECHNOLOGY:The advanced 4-stage staged combustion system operates with a minimum heat load of just 8,500 BTU, delivering comfortable hot water in summer without mixing cold water and sufficient heating output in winter, while improving overall energy efficiency. HIGH-EFFICIENCY PURE COPPER HEAT EXCHANGER:Built with a 100% pure copper heat exchanger, this natural gas tankless water heater achieves up to 95% thermal efficiency, provides hot water within seconds, minimizes heat loss, and ensures reliable, long-lasting performance.The compact 21.3″×13.7″×6.8″wall-mounted design supports standard 3/4″ NPT water and gas connections, 3″vent, and a UL-approved 120V power supply for easy installation. MULTIPLE SAFETY & ANTI-FREEZE PROTECTIONS, EASY INSTALLATION:Designed for indoor use, this unit includes overheat protection, anti-dry combustion, low water pressure start, anti-scald protection, flame failure protection, dual gas solenoid valves, and automatic anti-freeze protection below 39°F (4°C). This natural gas tankless water heater delivers instant and continuous hot water with a powerful 3.6 GPM flow rate and 85,000 BTU output, ideal for 2–3 fixtures at the same time. Designed for indoor installation, it provides stable water temperature without waiting or running out of hot water. Built with a pure copper water tank for excellent heat transfer and durability, this unit features constant temperature technology to prevent sudden temperature fluctuations. The 3/4" NPT connection ensures easy installation and compatibility with standard plumbing systems. With its compact, energy-saving design, this on-demand water heater is perfect for apartments and homes seeking efficient and reliable hot water using natural gas.