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Join Date: Feb 2001
Location: Cumberland County 5A
Actually, the bottom element maintains the water temp. The top element always get priority but is typically satisfied unless starting from cold or during high usage. Top elements are energized far less than the bottom but key to fried lower elements is limescale, as you mentioned.
Unless elec. water heater technology has changed since I retired, it's the opposite. But yes, tops come on frequently to maintain temps. Both in static condition, or when water is being drawn off.
Water heaters "refill" from the bottom up, as hot water is drawn from the top of the tank and the cold water introduced to replace it, comes in at the bottom of the tank vis a tube that goes almost to the bottom.
So it's the bottom element that heats the cold water as it comes into the tank. They can "run" for quite some time to reheat cold water coming in, which is why they typically fail first.
Replacement of top vs bottom elements runs about 90% bottom elements, to top elements. Any bottom element was replaced with a low watt density part. Or a sand hog, if the water was really hard?
Had two water heaters in my house over the 25 year period from building it, to selling it. The first one was slightly used and free, but bigger than I needed. It last about 6 years and rusted out, put a new 52 gallon in. Never replaced either top element during that time span.
Not a guess on my part, as I've probably installed a coupla hundred new ones and repaired far more than that, building houses/town houses and maintaining rental units, over a 40+ year period.
State water heaters were once fairly good units and I installed quite a few in the 70s and 80s. Then they went to hades back in the early 90s. Junk thermos/elements, often didn't make it a year. Some tanks never made it to the worthless 5 year rust out warranty. Because the free replacement was only warranted for the balance of the original unit.
After that, mostly used AO Smith or whatever units Lowe's had, for inexpensive water heaters in rentals. All of the Lowe's water heaters were still in use, some after 20 years, when I retired.
Some folks' learnin' curves just look like circles...3A Camp/also hunt 4B