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What is the difference between a single element and dual element electric water heater?
Friday, July 20, 2018
Most tank electric water heaters of 30 gallons or more are dual element, meaning that they have a top and bottom heating element at the side of the tank. Some older mobile homes have a single heating element for a 20 or 30 gallon water heaters, but nowadays the only single-element water heaters we see are 19 gallons or less, and they are used for a single application such as a bar sink. Also, the single-element water heaters are usually 120-volt, (single breaker in the electric panel) whereas the larger water heaters are all 240-volt (double breaker). Dual element water heaters are recognizable by the two raised access panels, one over the other as in the photo above, at the side of the water heater for each element, whereas the single element water heaters only have one.
Although dual element water heaters have two heating elements, only one element operates at a time. The top element comes on first and, when the water at the top of the tank has reached the temperature setting for the top thermostat, then the bottom element kicks in until its thermostat is satisfied. Dual element water heaters are rated as more energy efficient and have a faster recovery time that single element ones.
There is a peculiarity of dual element water heaters than can cause a trouble-shooting problem if the water heater is no longer working: because the top thermostat has priority and must be satisfied before the bottom element can turn on, if the top element is dead, the water heater will not work at all even though the bottom element is still good—because the top thermostat will never be satisfied and transfer power to the bottom.
Conversely, if the bottom element is fried, then it will work but the water may turn cold before the end of your shower even though the water heater is functional, because the bottom half of a tall water heater tank never get fully heated in the recovery cycle. So, a water heater that is completely dead may just have a bad top element, and a water heater that seems to be doing a poor job of heating the water probably needs a new bottom element.
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