Electric Resistance Water Heaters
Electric resistance water heaters operate by resistance elements within the water containment tank. These units can be equipped with either one or two elements. Most models have two elements, one located in the upper portion, and one in the lower portion of the tank. Each element has an individual thermostat control found behind the access plates. This is important to remember because when adjusting the tank's temperature, both thermostats must be adjusted, not just one.
As previously described, hot water is drawn from the top of the tank and replaced by cold water entering at the bottom through a tube.
When the demand for hot water is low, the lower heating element operates to maintain the water temperature. As hot water demand increases, the upper heating element comes on to maintain the water temperature. Hot water is drawn from the top of the tank, cold water is brought into the tank at the bottom and the lower heating element begins heating the entering water.