A.O. Smith ATM-199X3 Tankless Water Heater 10.5 GPM, 199,000 BTU

The A. O. Smith ATM-199X3-N Adapt® SC Tankless Water Heater is a high-efficiency natural-gas water heater designed to provide continuous, on-demand hot water for residential applications. With up to 199,000 BTU/h of heating input and a maximum rated flow of 10.5 GPM, it offers substantial hot-water capacity for professionally sized larger homes and demanding residential applications.

Unlike a conventional storage-tank water heater, the ATM-199X3-N heats water only when a hot-water fixture is being used. Its modulating operation adjusts heating output according to demand, helping reduce standby energy loss while supporting efficient natural-gas consumption.

With a 0.95 Uniform Energy Factor and ENERGY STAR® certification, this condensing tankless water heater captures additional heat from combustion exhaust before it leaves the system. This helps improve energy utilization while maintaining dependable everyday hot-water performance.

Integrated X3™ Scale Prevention Technology helps prevent minerals from adhering to the heat exchanger. This technology helps the unit maintain like-new performance for longer and eliminates the need for annual descaling under normal operating conditions, making it especially valuable for homes in hard-water areas.

The ATM-199X3-N combines a commercial-grade copper primary heat exchanger with a stainless-steel secondary heat exchanger. This dual heat-exchanger construction supports efficient heat transfer, corrosion resistance and dependable long-term operation.

The compact wall-mounted cabinet measures approximately 40.4 inches high, 17.1 inches wide and 11.9 inches deep. It can be installed indoors or outdoors with the appropriate A. O. Smith outdoor vent-cap kit, providing flexible placement for replacement projects and new residential installations.

A built-in digital control display allows convenient temperature adjustment from 100°F to 140°F, with a factory default setting of 120°F. The display also provides access to operating status, system settings and error information.

Electronic ignition, an included pressure-relief valve, internal freeze protection and Ultra-Low NOx operation further support safe and dependable performance when the unit is professionally installed according to manufacturer instructions and applicable local codes.

Key Features

Up to 199,000 BTU/h Heating Input
Provides substantial heating capacity for professionally sized larger homes and demanding residential hot-water applications.

Maximum Flow Rate up to 10.5 GPM
Supports high-flow on-demand hot-water delivery. Actual flow depends on incoming-water temperature, required temperature rise, water pressure and simultaneous demand.

Continuous On-Demand Hot Water
Heats water when required and provides a continuous supply when properly sized for the property’s hot-water requirements.

0.95 UEF Efficiency
Uses condensing technology to capture additional exhaust heat and support efficient natural-gas operation.

ENERGY STAR® Certified
Meets ENERGY STAR® requirements for qualifying high-efficiency gas water heaters.

Integrated X3™ Scale Prevention
Helps prevent mineral buildup, maintain heat-exchanger performance and eliminate annual descaling under normal operating conditions.

Dual Heat-Exchanger Construction
Combines a commercial-grade copper primary heat exchanger with a corrosion-resistant stainless-steel secondary heat exchanger.

Built-In Digital Control
Provides convenient temperature adjustment, operating information, system settings and error-code display.

Adjustable Water Temperature
Supports water-temperature settings from 100°F to 140°F, with a factory default setting of 120°F.

Low-Flow Activation
Activates at approximately 0.4 GPM and supports continuous firing at approximately 0.26 GPM.

Ultra-Low NOx Operation
Reduces nitrogen-oxide emissions while maintaining dependable natural-gas performance.

Flexible Condensing Venting
Supports approved PVC, CPVC and polypropylene venting in two-inch or three-inch configurations, subject to manufacturer instructions and applicable codes.

Indoor or Outdoor Installation
Supports indoor installation or outdoor mounting with the appropriate A. O. Smith outdoor vent-cap kit.

Compact Wall-Mounted Design
Measures approximately 40.4 × 17.1 × 11.9 inches and weighs approximately 83 lb, helping preserve valuable floor space.

Cascade Capability
Allows up to 12 compatible units to operate together in applications requiring greater combined hot-water capacity.

Residential Warranty Protection
Includes a 15-year limited heat-exchanger warranty and a five-year limited parts warranty for qualifying residential applications. Manufacturer terms and conditions apply.

Why Buy the A. O. Smith ATM-199X3-N Tankless Water Heater?

The A. O. Smith ATM-199X3-N is a strong choice for homeowners seeking high-capacity, energy-efficient hot water without the floor-space requirements of a conventional storage tank. Its 199,000 BTU/h maximum input, 10.5 GPM maximum rating, 0.95 UEF and dual heat exchangers provide a dependable combination of performance, efficiency and durability.

Integrated X3™ Scale Prevention Technology, ENERGY STAR® certification, digital temperature control and flexible indoor or outdoor installation further improve convenience, durability and installation versatility. Contact Jimmy HVAC for a free quote and professional assessment to confirm whether the ATM-199X3-N is the correct capacity for your home.