ECN Forum Forums General Topics of the Trade General Discussion Area Load Calcs and tankless water heater

Do you figure the water heater at 100% of it's full load KW rating? I have a customer with a 200 amp service. Present load calcs come to 123 amps without water heating. They want to add a Tempra 24KW tankless water heater. I know code doesn't care about occupancy but as a side note there is only one occupant.