For even heat distribution, it is best to place the heater in the center of the tank so an even flow of liquid passes through each hairpin element and effectively removes the heat from the sheath. The bundle should also be at the bottom of the tank as heat rises and it will heat upwards in a linear fashion. Another good practice is to place a thermostat or thermocouple probe at the other end of the tank so that the operating temperature will account for the location farthest from the heater. This could ensure an even heat distribution so long as the tank is well insulated. In the image to the left, you can see the elements need some maintenance (there is a collection of sedimentation on the sheaths) but the location of the heater is well placed.