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Old 12-16-2022, 12:42 PM   #101
DickR
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(2) My new plan: I opened up the panels on the heater and found that it only has one thermostat, at the top. I'm thinking of disconnecting the lower element. I think the top element would provide enough hot water for a good shower. Two questions: (1) Do you see any problem with this plan? (2) Can I disconnect the lower element myself? How would I do that? What would I need to be careful about? (Response: Turn off the breaker. )...
Something doesn't make sense in the thermostat configuration you describe. As an element heats water around it, that water, considerably hotter than the bulk water away from the element, rises and displaces cooler (well, less hot) water until the heated water meets water at the same density/temperature. While there certainly is some mixing and heat transfer in this convective flow, in general the level of sufficiently hot water moves downward toward the element doing the heating until the thermostat controlling power to the element is satisfied.

As I explained back on Sept 30 (post #92), I would expect there to be a thermostat associated with the lower element. When the upper one is satisfied, it would turn off power to the upper element and switch to powering the bottom thermostat/element. When the level of sufficiently hot water got all the way down to the lower thermostat, then the thermostat would shut off power to its element, and it would be that element that would come back on first if hot water use brought the hot/cold interface back up over that point. If continued hot water draw brought the interface level up to the upper thermostat, then that one would cut power to the lower thermostat and turn its own element back on.

This leads to questions. If there is only one thermostat, at the top, and it controls power for both elements, then it would turn off when the hot water level comes down to that thermostat, at which point heating would stop altogether, and the water in the tank between the two elements never would reach the set point. How would the lower element remain on long enough to finish heating all the water in the tank? If the upper thermostat controls only the upper element, when would there be any power to the lower element, and what would control power to it? Safety requires control of power to that element.

Actually, never getting enough hot water for more than one short shower, followed by recovery of hot water availability after a short time, usually means failure of the lower thermostat or element. Not getting any hot water at all usually means failure of the upper assembly.

Given that you have two heating elements, each would have its own thermostat, for control purposes. The look and function of the upper element/thermostat assembly will be different from that of the lower one; they are not interchangeable. If one fails, the correct type must be used for replacement.

As to disconnecting the lower element, to save power by not having the entire tank contents kept hot, yes, that could be done. Be sure to turn off the breaker before fiddling in there, and put twist caps on the wire ends, for safety. It might also be a good idea to attach a clear note to the tank, explaining what's been done and why.

I have to wonder about how much power use would be saved by disconnecting the lower element. Some savings would come from reduced heat loss from the lower half of the tank to its surroundings, since the water there would be cooler than at the top and the rate of heat loss is proportional to temperature difference between hot water and cold surroundings. Still, the hot water at the top of the tank will be cooled at some considerable rate by direct conduction of heat from hot water to the cold water below and in direct contact with it. The thermostat will come on regularly to keep the top water up to setpoint. With both elements wired, it would be the lower element that would cycle on and off to replace heat loss, but the loss rate would be somewhat higher.

I do think that the same overall power savings can be achieved without disconnecting the lower element simply by adding a lot of insulation around the tank and piping. Heat transfer in this situation is governed by Fourier's law: Q = U*A*dT, where Q is rate (BTU/hr), U is a heat transfer coefficient (BTU/sq.ft/hr/degree F), A is area of heat transfer, and dT is temperature difference (F). Insulation value R is defined as 1/U, so that the heat loss equation could be written as Q=A*dT/R. The important thing to note is that cutting U in half, by doubling insulation R, cuts the rate of heat loss in half. At some point there is little additional saving to be had by increasing total insulation R (more thickness). But we are talking about just a water heater, so the total area involved is small, and adding even more insulation is cheap.
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Old 12-16-2022, 02:49 PM   #102
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Dick, I will remove the upper and lower panels and take photos of what's in there when I get a chance.
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Old 12-16-2022, 02:58 PM   #103
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I think it would be easier to move to Florida.....
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Old 12-16-2022, 03:31 PM   #104
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Is Florida providing free hot water?
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Old 12-16-2022, 05:41 PM   #105
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I think it would be easier to move to Florida.....
Me too! I am amazed there is so much to say about heating with wood and water heaters.
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Old 12-16-2022, 06:34 PM   #106
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Me too! I am amazed there is so much to say about heating with wood and water heaters.
Why wouldn't there be? Entire books have been written on these topics and people make their living with wood heat and water heaters. For your entertainment:

https://microbiomejournal.biomedcent...168-015-0134-1
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Old 12-16-2022, 10:06 PM   #107
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Is Florida providing free hot water?
In one one sense--yes!

Florida's city water comes out of the ground much warmer!

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Sailin, is this a hobby for you?
It is a hobby for me!

With three houses, three woodstoves, three water heaters--two using lake water--I try to share my efforts to keep inflating costs to a minimum.

One house has county-supplied water, which kills bacteria. A water heater which heats only 15 minutes a day--using the breaker--doesn't have time to grow deadly bacteria.

Downstairs, I source my clothes washer through both hot and cold water faucets, although only cold water reaches the washing machine. Put another way--except for the 15 minutes for showering, the water heater stores only cold water in it.

******************* link deleted***************

If you have a need for regular use of a dishwasher machine, then saving utility costs in this manner will always appear cumbersome.

I like beating the system!

Last edited by ApS; 12-17-2022 at 05:03 AM. Reason: Link deled per request
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