Abstract: A water heater including a cabinet having an inlet, an outlet, and a flow path disposed between the inlet and the outlet and having a plurality of upper and lower junctions to redirect the flow path. Each lower junction includes a drain port. A flow rate sensor measures the flow rate of the fluid through the flow path, an inlet temperature sensor measures an inlet temperature, an and outlet temperature sensor measures the outlet temperature. Heating elements are disposed along the flow path between the inlet and outlet temperature sensors, and intermediate temperature sensors are disposed adjacent respective heating elements to measure an intermediate temperature within the flow path. A controller operates the heating elements to heat a fluid within the flow path to a predetermined set point temperature based on the measurements of the flow rate sensor and temperature sensors.