An electric heater system includes an inlet, an outlet, a plurality of heat exchanger assemblies, and one or more connectors. The plurality of heat exchanger assemblies are connected in series. Each heat exchanger assembly includes a vessel, heating elements disposed within the vessel, and a fluid guide member. The connectors secure the vessels of the plurality of heat exchanger assemblies to each other. The connectors are also in fluid communication with the vessels. Fluid entering the inlet flows through the heat exchanger assemblies and through one or more connectors where it exits the outlet. The fluid guide members of the heat exchanger assemblies are of different or the same combinations to generate a predetermined pressure drop between the inlet and the outlet.