A.O. Smith ATO-340H-P Technical Documents | Page 5
• This manual provides information necessary for the installation, operation, and maintenance
of the water heater.
• The model description is listed on the rating plate which is attached to the side panel of the
• Please read all installation instructions completely before installing this product.
• If you have any problems or questions regarding this equipment, consult the manufacturer or
its local representative.
• This equipment is an on-demand, tankless water heater designed to efficiently supply endless
hot water for your needs.
• These high efficiency models have a built-in secondary heat exchanger that absorbs latent
heat from the exhaust gas.
• The 240 Indoor (T-H3J-DV), 340 Indoor (T-H3S-DV) and 540 Indoor (T-H3-DV) models are
only to be installed indoors. The 240 Outdoor (T-H3J-OS), 340 Outdoor (T-H3S-OS) and 540
Outdoor (T-H3-OS) models are only to be installed outdoors.
• The principle behind tankless water heaters is simple:
*This diagram illustrates tankless water heater design concepts only and does not accurately
represent the water heater’s physical description.
1. A hot water tap is turned on.
2. Water enters the heater.
3. The water flow sensor detects the water flow.
4. The computer initiates the fan motor and sends a signal to the igniter to create an ignition spark.
5. The gas ignites and flames appear within the burner chamber.
6. Water circulates through the heat exchanger and then gets hot.
7. Using thermistors to measure temperatures throughout the water heater, the computer modulates
the gas and water valves to ensure proper output water temperature.
8. When the tap is turned off, the unit shuts down.
Cold water inlet
Hot water outlet
Water control valve
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