Scaled up electric water heater element

Ken_40

However, energy consumed is designed to heat the element, hence the water. Heating the element is fine, however, heating the scale is wasted energy, because the scale displaces water, that should be heated - instead of scale.

True, that is a very tiny amount of wasted energy and you are correct, the scale will always liberate its energy into the water - eventually. The real issue becomes apparent when we see the 'U' element actually embedded and jumpered by scale, thus, reducing effective surface area of water to element contact! The scale in this case becomes an insulator. True again, it is not a great insulator, but considering the cost of electriuc energy, even a small amount of insulation will be costly IMO, perhaps on the order of 5-15%? 24/7/365?

Then too, despite the cheap cost of replacing elements, the labor can be a killer.

Eric Johnson

Scaled up electric water heater element

Here’s a simple question that there seems to be some disagreement on:

Is a scaled-up water heater element less efficient than a clean one?

Alliant Energy, Wisconsin’s electric utility, recently ran a television segment on water softeners, in which they claimed that scale increases electricity usage. I don’t think that’s true. While a scaled-up element will certainly overheat and fail before a clean one, it seems to me that all of the electricity going to the element results in heat, which eventually finds its way into the water. It may take longer to heat the tank, but it won’t draw more juice in the process.

The story is completely different with a gas or oil-fired water heater, of course, since heat that is not absorbed by the water in a scaled-up tank goes up the stack. But with electricity, efficiency is lost in the form of heat, which in the case of a water heater, is all good.

Have I got that right?

kevin coppinger_4

if you have...

240 going to the tank for a longer period of time won't that cost more? kpc

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Eric Johnson

voltage vs kwh

I don't think the voltage has anything to do with it. Your electric bill is based on kw/h consumed.

The way it was explained to me (and I don't know, which is why I'm asking) is that the heat output of electricity is limited to about 3,400 btu per kw hour. So, while it may take longer to generate the same amount of heat, it will draw the same amount of electricity over that time period.

Put another way, the draw depends on the load. Less load (i.e., a restricted ability to transfer heat) means less draw.

hr

I would guess at some point

enough scale build up could all but eliminate any heat transfer. I know when the tanks fill with sediment in the bottom the tanks produce alot less output, and they run for hours trying to recover.

There is also a limit to how many watts per surface area an element can output in a tank. To get additional output you need flowing water across the element to "scrub away" the heat output or the element will self destruct. Same as they do when they get covered in sediment in the bottom.

Contact a Chromolox rep for additional info.

hot rod

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Noel

If you draw the same current at the same voltage,

But you have less heat transfer, then the element is retaining that heat, no?

It can't do that for very long.

As long as it is drawing that amount of electricity, it is putting out that amount of heat, or it is at the moment of it's destruction, the way I see it.

You haven't changed the resistance. I don't buy that it can store unused heat in the element, and I don't buy that it will run longer. It will fail if the element cannot release the heat that it has made.

That's my opinion.

Noel

ALF

The scale should in no way effect the resistance of the element. That means that the same amount of heat will be produced regardless of the scale, until it burns in two because there is not enough water in contact with the element to dissapate the heat. In the short term, I think that the heat will be lost to the outside of the tank through the element plate.

Mitch_4

lime and calcium scale

build up will not change the resistance of the elements. It WILL affect the heat transfered to the water it is heating because it is an insulator.

This has 2 results.

1- Increased heat being retained by the element shortening it useful life expectancy, and will practically guarrantee a failure.

2- By limiting the heat transfer, the element works for a longer duration to transfer the energy required. This results in longer run times (more $$$ to operate) and compounds problem number one.

Other associated costs are service, water treatment, parts, less showeer time because the recovery rate is reduced etc.

Mitch

Unknown

So energy in doesn't always equal energy out?

That's bunk, bunky.

If it runs longer at the same volts and amps, it makes MORE hot water, not the same amount of hot water.

In your example of running longer at more dollars of electricity, where does the extra energy go? If it didn't go "into the water as fast" but it used a higher number of watthours, explain where the extra energy went, please.

Noel

Glenn Sossin_2

It runs longer??

It would seem logical that the scale build up would reduce the efficiency of the energy transfer. Even though the heat energy would eventually find its way to the water in theory, isn't it going to run longer to do this and cost more energy in the process ??

LarryC

Extra energy went where?

I believe that the element will run at a higher temperature trying to push the heat thru the scale. As the element temperature goes up, the resistance of the element will go up, and the current draw will go down. Also as the element runs hotter, the losses to the tank shell will go up because the RATIO of the thermal resistance of the tank shell heatsink to the water will APPEAR to go down. Therefore more losses. Which means the heaters will be energized longer to produce the same amount of hot water.

amhplumb_2

Scaled Water Heater Elements

In theory, the heat has to go somewhere, so yes, even though the scale is an insulator, it should eventually heat up and transfer heat to the water. Granted it would take longer. However, I agree with some of the other posts that the heat being insulated by the scale would remain in the element, causing it to operate at a higher temperature. I would surmise the higher temperature would cause the element to break down eventually, because the heat is not being transferred to the water as quickly as it would without the scale. Run an electric water heater without water in it sometime (DON'T DO IT BUT JUST THINK ABOUT DOING IT FOR A MOMENT!) In theory, the heat should transfer to the air albeit longer than it would take to transfer to water, however, the element will break down very quickly before it does, because the element can't transfer to it fast enough to the air! Over the years, most of the water heaters that I've installed and serviced are natural gas, however, on the handful of electric ones, including a large three-phase one recently, that I have serviced, I don't remember ever replacing a defective element that wasn't covered with scale! Also, the scale probably accelerated corrosion of the element! Another topic! Scale just can't be good. And back to the original post's thought on wasting energy, probably very little waste of energy! However, the scaled elements will still cost you in the long hall! Just my thoughts!

Mitch_4

I am speaking

about the effect of heat transfer to the water, the heat that is not trasfered is damaging the elements.

Its like lime scale buildup inside a cast iron heat exchanger, it impedes the transfer does it not? or does your gas fired unit (or oil...whatever) have to run longer to effect the same heat transfer to the water?

If not, then boiler maintenance on the water side would be a non issue.

"If it runs longer at the same volts and amps, it makes MORE hot water, not the same amount of hot water"

No..it makes the element produce more heat..not the same as heating water. When you limit the transfer of heat from the element to the water, you are not doing so as effectively. Watts consumed will rise as the heat does not get absorbed by the water, longer run time and damage to the element.

Mitch

Noel

Great theory

Those elements weigh less than a pound.

The point I'm trying to make is that if the element cannot DELIVER the heat that it makes, it is seconds from burning out, therefore, your theory only applies to that time frame.

As long as the element is drawing energy, it is making heat.

How much of that heat can you store in a one pound element?

On a boiler that has fuel burning in it, there are TWO paths for heat, the water or the vent pipe. On an electric boiler that has "slow" heat transfer, where is the rest of the heat going?

If it uses the electricity, it converts it to heat, and within moments, that heat is out of the element and into the water, or the element blows. Been there, seen that.

Noel

jp_2

larry has it right

i think larry has it right, scale increases the electrode temp, increasing its resistance, lowering its power consumption taking longer to heat the tank.

scale should give the appearance of a smaller heater element.