Instantaneous water heater circuit breaker sizing

[faresos]

Hello All:

Reading the brochure of several instantaneous water heaters it appears they size the beaker based on 100% of the load not 125%. Does this mean they consider this to be non-continuous load? I have been sizing it at 125% but should I follow the manufacturer recommendation which is 100% of the rating?

Thanks,

 

[infinity]

Unless the heater is running at full load for 3 or more hours it is not considered a continuous load according to the NEC. Storage type water heater require the 125% factor because is an NEC requirement. I would follow the manufacturers instructions.

 

[Dennis Alwon]

Instantaneous heaters are not considered continuous. it would be a very unusual circumstance when the heater would run for 3 hours. In a residential setting, I doubt that would ever happen.

 

[JFletcher]

Tankless/on-demand water heaters are not continuous loads and thus can be sized at 100%, unless the mfg requires 125%, then 110.3(B) would come into play.