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Should the top and bottom water heater thermostats be set to the same temperature?

I did a quick google search and saw all kinds of differing opinions. for instance, this guy seems like he knows what he's doing:

http://www.youtube.com/watch?v=RCDvHIcPreo&t=2m09s

and he said the top thermostat should be set to a higher temperature than the low one, but other places I've read said they should be at the same temperature.

my water heater's old, if that makes a difference. I didn't see a date, but the energy sticker had some reference to 1994. sorry I don't have more info; the thing's wedged back in a tight closet and hard to get to.

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up vote 5 down vote accepted

Setting the top element slightly higher helps the elements to be used evenly. If you set them to the same temperature, the bottom element will be the first one on every time, and frequently the only one used to maintain the temperature. If you set the top element too much higher, then it will be used most of the time, and the bottom element acts more as a pre-heater.

Having them used evenly will spread out the minimum time to replacement. But I wouldn't go through too big of an effort to change the settings on an old water heater. Whenever your elements do go, or whenever you decide to change the temperature, that would be the time to make this adjustment.

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I am changing the temperature which is why I'm asking. What should the difference be? 5 degrees (F), 10? Thanks! – bmaupin Jun 29 '11 at 19:41
    
When you change it, you'll be able to tell the temperature difference in the tank by when each element clicks on or off. If you can't get them exactly the same, and you're not using any water at the time, err on the side of having the top element activate slightly more. Cold water coming into the tank when water is running will reverse that balance. – BMitch Jun 29 '11 at 19:47

The top element is always the first one on. In fact the bottom element does not receive power until the top thermostat is satisfied. I’m guessing that setting your top thermostat to a 150 would give you small amount of really hot water rather quickly, while setting the upper and lower thermostats evenly to a moderate temperature (115-125) would be your quickest way to get a full tank of hot water.

http://waterheatertimer.org/How-water-heater-thermostat-works.html

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That last guy is exactly wrong, there are dip tubes the run the incoming and outgoing water from the bottom. As you turn on hot water it exits the heater from the bottom and the cold water enters from the bottom, your bottom element will come on first. If the bottom element does not come on it means the dip tube in the tank is broken ( it happens) and you are pulling from the bottom but feeding to the top.

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Hello, and welcome to Stack Exchange. Hot water leaves the heater tank from the top, as that's where the hottest water is. Take output water from the bottom, and you'll be taking the coldest water in the tank, which doesn't make sense. – Daniel Griscom 19 hours ago

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