Abstract: A tankless, flow-through electric water heater whose housing is designed for modular application, where serially connected modules define the path of the fluid being heated, in this case water, through the heater from inlet to final outlet. Each module contains two separate chambers and each chamber is provided with an electric immersion type heating element. The first and last chambers will also have a temperature sensor which will signal an electronic temperature control system. The temperature sensor in the first and last chambers provides signal inputs to energize each heating element of each chamber for a period of time proportional to the temperature difference between first chamber and the desired set leaving temperature of the water, which is set by an adjustable temperature controller (potentiometer), included in this control system. This control system also has a minimum setting point for a "no flow" condition or for the prevention of water freezing, where extreme weather conditions exist.