A. A high density element is able to transfer more energy flow (higher temperature) per square inch to the water in the water heater but these higher temperatures will wear out the element much quicker than a lower density element. If you have scale build-up a high density element will need to generate this higher temperature for a longer length of time to transfer energy through the added coating on the element which will then cause it to burn out quicker. Lower density elements operate at lower temperatures per square inch so if they encounter a scale build up, the higher amount of energy needed to get through the added coating does not cause the element to get hot enough to burn out the element. A lower density element tends to last longer.