Tempra Plus tankless electric water heaters features Stiebel Elton’s exclusive Advanced Flow Control to automatically adjust the flow rate, if needed, in order to keep the output temperature constant and supply continuous hot water to the open draw-off points. In other words, if the water flow rate is greater than what the heater can provide given the outlet temperature setting, the Advanced Flow Control automatically adjusts the flow rate just enough to maintain that set point temperature. There’s no need to worry about a cold water surprise in the shower.
Hot water needs vary between geographic locations and home to home. In general, all Tempra models 12 -15 can run on a 100 amp incoming electric service, models 20-29 on a 200 amp service, with the 36 requiring a 300 amp service. Have your electrician confirm the respective system load capacities and panel space requirements. Besides the electrical, the optimum size depends mostly on the incoming water temperature and number/size of fixtures in the house.