Storage type water heaters >120 gallons

[Cold Fusion]

What are the issues for a storage type water heater more than 120 gallons? I'm being asked about a 150 gallon WH. Interestingly, most of the commercial grade water heaters only go up to 119 gallons.

Here is all I have found:
422.13: For WH less than 120 gallons, shall be considered continuous load for sizing branch circuit. So if the the tank is 121 gallons, it is not considered a continuous load? That doesn't seem like a good idea.

422.11.F.1: Limited to 48A circuits unless covered by F.3

422.11.F.3: If the unit is an asme rated and stamped tank, then can have heating element circuits up to 120A.

Is this a Mechanical Code issue? Above 120 gallons the vessel must be ASME rated? That would make sense. An ASME rating would really jack up the cost.

Anybody got any clues?

cf

 

[bphgravity]

422.13: For WH less than 120 gallons, shall be considered continuous load for sizing branch circuit. So if the the tank is 121 gallons, it is not considered a continuous load? That doesn't seem like a good idea.

Not exactly. A 120+ gallon water heater can still be considered a continuous load if it can be determined the 3hr threshold will be met. 422.13 makes that determination for you on the smaller appliances. For these appliances the branch circuits typically utilize smaller insulated conductors which are at a greater risk of overload, thus, the 125% factor is mandated.

422.11.F.1: Limited to 48A circuits unless covered by F.3

422.11.F.3: If the unit is an asme rated and stamped tank, then can have heating element circuits up to 120A.

Is this a Mechanical Code issue? Above 120 gallons the vessel must be ASME rated? That would make sense. An ASME rating would really jack up the cost.

There is no specific requirement for ASME rating in either the mechanical or plumbing codes. It is however, a component of the UL 1453 listing criteria for certain vessel and tank types.

 

[Cold Fusion]

BP -
Thanks for the reply. I haven't found any thing else. I'm going to enlist one of out mechanicals.

I did get the UL listing - but it wasn't too interesting.

cf