An electric water heater element is made of metal and heats up due to electrical resistance in order to warm the water in an electric water heater. Electric water heaters have both an upper and a lower water heater element as opposed to gas water heaters, which use gas burners.
The lower water heater element does the majority of the work in heating the water for an electric water heater as the cold water supply enters the water heater near the bottom of the tank. The upper water heater element is used to heat the water in the top portion of the tank and is mainly used when hot water is in high demand. Replacement water heater elements should be the same voltage/wattage rating and style as the old ones.