A.O. Smith ATO-340H-P Technical Documents | Page 7

A.O. Smith Water Heater Technical Documents - ATO-340H-P.
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1.  Follow all local codes, or in the absence of local codes, follow the most recent edition of the National 

Fuel Gas Code: ANSI Z223.1/NFPA 54 in the USA or CAN/CSA B149.1 Natural Gas, Propane Installation 

Code in Canada.

2.  All gas water heaters require careful and correct installation to ensure safe and efficient operation.  

Thismanualmustbefollowedexactly. Readthe“SafetyGuidelines”Section.

3.  The manifold gas pressure is preset at the factory.  It is computer controlled and should not need 


4.  Maintain proper space for servicing. Install the unit so that it can be connected or removed easily. 


5.  The water heater must be installed in a location where the proper amount of combustible air will be 

available to it at all times without obstructions.

6.  The electrical connection requires a means of disconnection, to terminate power to the water heater 

for servicing and safety purposes.

7.  Do not install the unit where the exhaust vent is pointing into any opening in a building or where the 

noise may disturb your neighbors.  Make sure the vent termination meets the required distance by 


8.  Particles from flour, aerosols, and other contaminants may clog the air vent, build up and reduce 

the functions of the rotating fan, cause improper burning of the gas, or cause damage to the water 

heater. Regularlyensurethattheareaaroundtheunitisdust-ordebris-free. Regularmaintenanceis

recommended for these types of environment.

9. The240Indoor(T-H3J-DV),340Indoor(T-H3S-DV),and540Indoor(T-H3-DV)aretobeinstalled

       indoors only.  These units are equipped with a thermistor and hi-limit switch for the exhaust gas,

       detecting excess temperatures within the flue and enabling the unit to safely stop operations if 

       needed.  These components are always monitoring exhaust gas conditions in order to prevent heat


       is used.  If the exhaust gas temperature exceeds 140 °F, these components will enable the unit to

       safely stop operations.  (For the Outdoor model, these components are not available since there’s 

       no exhaust venting required.)

•TheIndoormodelrequiresa3"or4”make-upintakeairsupplypipe. Theintakepipemustbe

sealed airtight.



•SidewallventingisrecommendedfortheIndoormodel. Verticalventing(rooftermination)is


•The manufacturer recommends running the exhaust vent and the intake pipe as parallel as possible.

10.  The 240 Outdoor (T-H3J-OS), 340 Outdoor (T-H3S-OS), and 540 Outdoor (T-H3-OS) models only to be

       installed outdoors and only in the area with mild, temperate climates.

       The Outdoor model shall be wall-mounted or mounted on a stand.  Locate the Outdoor model in an

       open, unroofed area and maintain the following minimum clearances:




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