Can a 240V water heater be converted to 120V?


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Old 12-07-22, 02:29 AM
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Can a 240V water heater be converted to 120V?

I bought a new 12 gallon water heater off Craigslist a while back. Before doing so I looked up the specs and saw it was 120V which is what I needed, so I bought it. Now, months later, I am ready to install it and find it is actually a 240V water heater.

What are my options? I want it to be safe and meet code. Can I run this on 120V as is? Can I install a 120V element? Or should I just resell it and move on to the appropriate 120V model?
 
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Old 12-07-22, 05:39 PM
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Just make sure the tank has water in it before hooking up power! or you risk burning out you element
 
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Old 12-07-22, 07:09 PM
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The same rules apply as for gas water heaters: Shut off the power-- both the breaker and the required shutoff switch near the tank.-- before draining the tank. See water gushing from a hot faucet for a minute before turning the breaker back on.

One hundred twenty volts into the 240 volt element without water in the tank can still burn it out.very quickly.
 
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Old 12-07-22, 07:24 AM
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At 240 volts the element draws 6 (6.25) amps to provide 1.5 kilowatts of heat. At 120 volts the same element will draw fewer amps (roughly 3, producing roughly 0.4 KW of heat) so there is no problem with continuous versus intermittent load calculations. Go ahead and hook the heater up to a 120 volt circuit if you want to, temporarily.
 

Last edited by AllanJ; 12-07-22 at 07:41 AM.
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Old 12-07-22, 07:30 AM
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You can simply just connect it to 120 volts and it will work. It will take longer to heat up but it will work. I have a 40 gallon unit that has been running this way for 10 years at my cottage.
 
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Old 12-07-22, 07:53 AM
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Oh, by the way, at 120 volts, according to my calculations, the water inside will still reach the maximum recommended temperature of 120 degrees F.
 
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Old 12-07-22, 10:47 AM
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It doesn't matter the size of the element or wattage. If no water is used it will reach maximum temperature..... eventually. One good thing.... a 240v element running on 120v will probably never burn out.

On the other hand... you could probably replace the 240v element with a 120v element.
 
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Old 12-07-22, 11:13 AM
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Pretty much universal. Either bolt in or screw in.
 
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Old 12-07-22, 01:45 PM
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Half voltage will result in approx 1/4 wattage. 1500/4=375W
That will result in loooong time to heat it up, but only use approx 1.2 Ampere.
You can not rouin anything by testing. It will probably need to run to the next day to be hot.

 
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Old 12-08-22, 06:24 AM
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You will have a choice of element wattages. If you choose a 1500 watt 120 volt element then go back to the posts above (I think #4 and #7) regarding continuous versus intermittent load. You may well need to upgrade the wiring and, if you need to string a new circuit you might as well do it as a 240 volt circuit.

Fifteen hundred watt space heaters are sold everywhere for use on 15 amp circuits

 
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Old 12-08-22, 06:31 AM
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Yet a (theoretical here) 1500 watt 120 volt water heater violates the intermittent/continuous rule on a 15 amp circuit (it needs 15-1/2 amp circuit, round that up to 20 amp circuit to comply). But you have to draw the line somewhere and the NEC code book uses 80% of the circuit and breaker amps rating as the maximum for continuous loading, (Or a 125% fudge factor to, given the actual loading, figure out the needed circuit amps rating) It is too complicated for me to describe here a variety of circuit wattages and element wattages to match different permutations of goals and objectives.
 

Last edited by AllanJ; 12-08-22 at 06:56 AM.
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Old 12-09-22, 04:52 PM
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A lot of discussion over circuit size. I don't believe the OP has ever mentioned circuit size here.
My point was there are two styles of element in use.... it's either A or B.
 
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Old 12-07-22, 03:42 AM
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How many watts is the element? What is the intended purpose? Twelve gallons sounds like for a small bathroom sink and nothing else. Do you have a dedicated circuit for this?
 
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Old 12-07-22, 03:44 AM
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The element is 1500W. This will only be used to heat water for a utility sink in the garage. I do not have a dedicated circuit for this.
 
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Old 12-07-22, 05:10 AM
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Halving the voltage will half the wattage the element can produce. This will increase the time to heat the water to any temperature. Only you know the time and temperature that is acceptable for your purposes. Operating a 1500 watt element at 120 vac draws 12.5 amps. This leaves little room for other loads on a 15 amps circuit without tripping breaker.
 
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Old 12-07-22, 05:19 AM
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Are you saying I could wire is up as if it were 120V? Black to black, white to red? Recovery time is not a big deal to me. I will use it to wash my hands periodically. The circuit is not dedicated, but is a circuit used by little or nothing else.

Based on what I reading, I can use the water heater as-is, but recovery time will be slow. And I run the risk of tripping a circuit breaker if trying to use other outlets on the same circuit? Correct?

The thing is, I already own this and cannot return it. My options are use it or try to sell it and get something else.
 
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Old 12-07-22, 06:24 AM
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My error. Halving the voltage will result in element producing one quarter the wattage since current is also halved because element resistance is constant. Suggest running a 240 vac circuit to the garage.
 
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Old 12-07-22, 06:41 AM
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Increasing the recovery time by 4 could make your water heater a continuous load. Plus, a breaker should not be loaded to more than 80% of its rated value. ​​​​​​​Unless this is a 20 amp circuit (#12 conductors fed from a 20 amp breaker), I would not recommend doing what you suggest. At a minimum it's inadvisable and could be dangerous. ​​​​​​​ I hope a pro will be along to explain it better.​​​​​​​​​​​​​​
 
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Old 12-07-22, 07:31 AM
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Thanks, AllanJ. I did not want to do anything questionable or, especially, unsafe. It sounds like the recovery thing is more of an inconvenience if anything.
 
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Old 12-07-22, 11:00 AM
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On the other hand... you could probably replace the 240v element with a 120v element
I don't think I will notice the slow recovery time as little as I will use this, but if I do I will try replacing the element as you suggest. Are these universal or would I have to buy one for this model and manufacturer?
 
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Old 12-08-22, 02:06 AM
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The replacement elements are cheap. Since it is a new install I may just install the correct 120V element now. Is the element the only real difference between a 240V and 120V electric water heater.
 
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Old 12-08-22, 05:47 AM
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If your water heater is on dedicated circuit (and it should be) then it is better to rewire the circuit to 240V. Just replace with 2 pole breaker matching wire size and move white wire from neutral to one of the poles on the breaker.
 
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Old 12-08-22, 06:28 AM
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If you choose a 1500 watt 120 volt element then go back to the posts above (I think #4 and #7) regarding continuous versus intermittent load. You may well need to upgrade the wiring
Good point. To be honest, at this point in my garage build I have no interest in running a new circuit. Reasons I won't boar anyone with. Based on that, I will likely stick with the current element. Like I said, this will be used for washing my hands when I happen to be working in the garage. Recovery time will not be an issue.
 
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Old 12-09-22, 04:40 PM
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Pretty much universal. Either bolt in or screw in.
I used to prefer the bolt-in elements, but haven't seen a water heater with bolt-in elements in years. I can't remember the last time I saw a replacement bolt-in element either.
 
 

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