Commercial Electric Tankless Water Heater

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Electricalhelp

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The plumbing design calls out for 44kW/208V/3P Electric Tankless Water Heater.

Does a Electric Tankless Water Heater considered a continuous load for calculating my Panel Schedules Load. (Demand at 100%)

Since I see section 422.11(F)(3), but doesn't say anything about continuous load.

But I notice section 422.13, but that's for a storage type water heater.
 
You'll want it calculated as a continuous load even in a panelboard you've got 120 amps per phase thats not negligible and there is a chance it'll have more than 3hours use continuous if there a demand for that size of water heater.
 
I've not seen an application where a tankless water heater has been a continuous load.
(Not relevant but note that 422.13 is for sizing branch circuits and not feeders or services-)
 
You'll want it calculated as a continuous load even in a panelboard you've got 120 amps per phase thats not negligible and there is a chance it'll have more than 3hours use continuous if there a demand for that size of water heater.

I’d contend that usually the opposite would be true - the larger the unit, the lower the duty cycle.
Only a specialized industrial process could require that much hot water continuously.
 
I’d contend that usually the opposite would be true - the larger the unit, the lower the duty cycle.
Only a specialized industrial process could require that much hot water continuously.
Even if water is drawn continuously, if the number of degree-gallons per minute (proportional to KW) is less than the maximum capacity the actual electrical power draw will be proportionally less, removing the need to calculate it as a continuous load.
 
I agree not required to be considered a continuous load. I would not bother to size the branch circuit with the extra 25% required for certain storage type water heaters.
 
Even if water is drawn continuously, if the number of degree-gallons per minute (proportional to KW) is less than the maximum capacity the actual electrical power draw will be proportionally less, removing the need to calculate it as a continuous load.

Agree. The only way it could possibly be continuous full load is if it was badly undersized.
 
Agree. The only way it could possibly be continuous full load is if it was badly undersized.
So in the few residential installs I've seen and done they cut things as tight as they can for winter temperature rise. There are minimum flow requirements to get the elements to turn on. For example I'm doing a shop with one that takes 80 amps 1phase but it has a minimum flow of 0.5 gpm which works here because it's a shop sink but the shower that's on the system is almost the max size for the unit. Obviously it won't be a continuous load in this instance but if there is a system that is large it depends on what's going to be flowing through at the minimum for it to kick on.
 
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