Water heater element, 240V vs. 120V?

[myredracer]

The output of resistive devices like a heating element, varies in proportion to the square of the voltage. So the 4KW element would produce (120/240 x 120/240) x 4,000 = 1/2 x 1/2 x 4,000 = 1/4 x 4,000 = 1,000 watts. It's as simple as this.

The 1,000 watt (rating at 120V) element at 120 volts draws 1,000/120 = 8.3 amps. The 4,000 watt element at 240 volts draws 16.7 amps (4000/240). Since the 4KW rated element draws 16.7 amps at it's rated voltage of 240V versus 8.3 amps, it has to be made of heavier gauge wire. If it's about the same price, can't hurt to try it.

*Maybe* if an element is rated to operate at a higher temperature, as in operation at 4,000 watts, the exterior sheath is heavier to withstand higher temperature. In that case, I could see some merit to the idea that it would last longer at 120 volts.

But it's not normally the internal wire that burns out first (assuming normal voltage & no surges), the exterior metal sheath fails first then water gets inside and then the total failure occurs. I doubt just having a heavier gauge internal conductor (the wire that the does the heating) increases the life much, if at all. I couldn't find anything on the internet to support that idea. It's usually minerals in hard water that is hard on an element and if the sheath is the same, it won't last longer. If they made stainless steel versions of the element, that would be a good choice, but I don't know if they do for RVs.

The forum is a little screwy at the moment because of the server changes and I can't post any links. Google "Rheem + heater element failures" for some info.

You should periodically inspect inside the heater to see if there is "crud" that needs to be cleaned out. If it builds up too much, that can be hard on an element. Also make sure the anode rod is good at all times.

[lwgmc77]

Originally Posted by targaboat

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.

So far it looks like the 240V elements have a thicker element compared to the 120V ones, I'm guessing to accommodate the higher voltage.

Our current 120V element was from a previous owner however it looks like it just deteriorated as the inside coil came out of the casing. The tank itself is in good condition.

Thanks,
Chris

[wa8yxm]

RVbyFred suggests you do that. The problem is this.. The 240 volt element when fed 120 volt will only generate about 1/4 the heat. I think my recovery rate is six gallons per hour with the 120 volt element.

So that would be four hours to re-heat.

IF There is anyone from ATWOOD or SURBURAN reading these threads I would like to make a suggestion.

Put in two ports for heat elements, put a 1,000 watt 120 volt in one, and in the other a 250 watt (Or even a 500 watt)

LOW-MED-HIGH switch on LOW I could use ELECTRIC on 30 amps, it would be enough to protect the water heater in cold conditions like tonight and still leave me power for heating or air conditioning in the summer (in the summer it would be enough to keep it HOT).

ON HIGH, I can take a shower.

[Hooligan]

Originally Posted by wa8yxm

RVbyFred suggests you do that. The problem is this.. The 240 volt element when fed 120 volt will only generate about 1/4 the heat. I think my recovery rate is six gallons per hour with the 120 volt element.
So that would be four hours to re-heat.
.

Still just 1 hour....
The 240 volt 4000watt will only generate 1/4 the heat on 120 volt. 1/4th of 4000 is still 1000watts. Your regular 120volt 1000 watt unit will heat 6 gallons/hour. So will the 240 volt unit operating on 120volts and producing 1000watts.

What if you put a dimmer switch in the line to the element, you could reduce your 120 volts to produce as little heat as you want...???