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Old 01-04-2014, 01:16 PM   #1
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Water heater element, 240V vs. 120V?

Hello...

We are needing to replace the electric heating element in a 6 gallon water heater in our RV. The current element is a 120V 1000 watt element. I was told to get a 240V 4000 watt element which would last longer than another 120V 1000 watt one. Is this true that the 240V element will last longer than a 120V one? The price is about the same either way. Any advice would be greatly appreciated. Thank you!!!!

Chris
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Old 01-04-2014, 01:46 PM   #2
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Quote:
Originally Posted by lwgmc77 View Post
We are needing to replace the electric heating element in a 6 gallon water heater in our RV. The current element is a 120V 1000 watt element. I was told to get a 240V 4000 watt element which would last longer than another 120V 1000 watt one. Is this true that the 240V element will last longer than a 120V one? The price is about the same either way.
Chris
Chris, (aka: lwgmc)
I've never heard that!

However, I do know that a 240V clothes dryer will run operate on 120V, but it will take 3-4 times longer to dry a load....(years ago I mis-wired a 240V dryer plug)!

IMO if a 240V element works on 120V, it may not heat as fast, or get the water hot, as a 120V element seeing 120 volts.

Hopefully someone who actually knows something will jump in here.
Mel
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Old 01-04-2014, 03:23 PM   #3
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Originally Posted by mel stuplich View Post
Chris, (aka: lwgmc)
I've never heard that!

However, I do know that a 240V clothes dryer will run operate on 120V, but it will take 3-4 times longer to dry a load....(years ago I mis-wired a 240V dryer plug)!

IMO if a 240V element works on 120V, it may not heat as fast, or get the water hot, as a 120V element seeing 120 volts.

Hopefully someone who actually knows something will jump in here.
Mel
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Mel,

Thanks for the quick reply! I did read up on this and the general consensus is that a 240V 4000 watt element will operate at 1000 watts at 120V. So, from what I've been told, it will heat the water the same as the 120V 1000 watt element. I guess the question is, if there are any issues using the 240V element and IF it will really last longer than the 120V one. Thanks!!

Chris
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Old 01-04-2014, 03:53 PM   #4
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Recovery/heat up time will be increased, but the 240 v element will last longer. You'll have to decide if the savings is offset by the recovery time. I'd personally go for the 120 v element and quicker, more hot water.
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Old 01-04-2014, 04:39 PM   #5
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A heating element is a resistive load, current is contingent upon the voltage applied to that load, If the element is 4000W and the voltage is 240V then there would be ~16A draw for 4kw. Since P=I(squared)R then R= ~.064ohms.

This resistance will remain constant so if 120V is applied to a load of .064 Ohms, then the current would be ~8A and the power would be ~960W. (amounts rounded)

Your advice, is relativly on track. The power is not markedly different than a 120V 1kw element but since the current is operating ~ 1/2 of that of the 240v 4kw element it should last longer.

Hope my quick math did not go astray, but I think this answers the question from a theoretical perspective.

Had I not rounded the power would likely have factored to 1Kw @ 120V logic tells me.
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Old 01-04-2014, 10:43 PM   #6
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Further to my previous post - given the consumed power, which is radiated as heat, is the same, logic and science says the heating time should be the same for each element operating with 120v.
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Old 01-05-2014, 09:21 AM   #7
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Further to my previous post - given the consumed power, which is radiated as heat, is the same, logic and science says the heating time should be the same for each element operating with 120v.
Libero,

Thank you for the great information. I too would expect the time to heat would be the same, since you said the resistance is the same. We may end up trying the 240V element afterall. They are close to the same price, and if it lasts longer I don't see what we have to lose. I had never heard of this trick, but it surprises me they would manufacture both elements (240V and 120V) since they are so close in price. Thanks so much!

Chris
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Old 01-05-2014, 02:37 PM   #8
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Makes sense to me. Can't see the downside. Especially if the cost is the same. Would be interested in seeing any empirically derrived or other scientific research data that says it does not make sense. If there is a cost delta, of course this is a different factor.

I took a roundabout way to show the restistive component. In fact with the restistance remaining constant, which it will in an element, and you halve the voltage, you will halve the current. This results in the power dropping from 4000w to1000w. A simple Ohms law equation will demonstrate this fact.

Good luck
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Old 01-05-2014, 08:51 PM   #9
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Pretty common industrial approach to get a longer heater element life. I often saw the spec for a heater element to be rated for the rated Watts and only used on 1/2 the voltage. Less tress on the element and a lower heat density.

Be sure you have the room to mount the larger element.

Ken
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Old 01-05-2014, 09:15 PM   #10
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Price about the same= same amount of material
Resistance about the same=same amount of material
Conclusion the two elements are physically about the same.

So how is one going to have a longer life.

Besides, an element will last for a very long time if it does not deteriorate from corrosion, or is not turned on while being covered with water, tank with not water, or large air bubble inside the tank. Both example of poor maintenance.
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Old 01-05-2014, 09:27 PM   #11
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the 4000w element is designed for 240v and the current would be 16.6 A. @ 120V there will only be 8.3A.

Less current in theory would say the element would last longer. It will only heat to 1000W this being 1/4 of the rated power. Again makes sense to me.
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Old 01-05-2014, 09:29 PM   #12
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For element life: I rarely replace elements that have just gone flat bad. Usually it's a side effect of water eating them up after the anode and it's main rod are gone.
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Old 01-05-2014, 09:31 PM   #13
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On any hot water tank I've had in a RV, the tank started to leak before the electric element or the gas burner gave out. Then I threw the whole thing away and put in a new one. But elements and the gas burner and related equipment do burn out.
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Old 01-05-2014, 09:37 PM   #14
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I have replaced burnt out elements in domestic and RV water heaters ove the past 50+ years. They do indeed burn out. Just like a lightbulb. After so many hours expect them to burn out.
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