# 240 VAC Water Heater



## tvl (Nov 14, 2018)

This might be considered a dumb question, but I'm going to ask anyway:

We own a Honda EU3000is that was purchased for power outages, but sees *very little* service; which is probably considered a good thing! The chances for us to encounter an *extended* power outage in our area would be very unlikely, but I do like to be prepared for the worst case scenario. In the event we were to ever lose power for more than a day, there might be a need to provide hot water for bathing, etc.

I have a 36 gallon, 240 VAC water heater which utilizes two 4500 watt heating elements. It would be easy to access our home's power panel and remove the 240 VAC power leads that feed the water heater. I could then run a power cable from the 120 VAC receptacle on the generator to the loose ends in the power panel and wire the heater for 120 VAC (hot, neutral & ground).

1) *First,* this may never likely need to be done, but I do want to be prepared should the need arise. In other words, have the appropriate materials readily available, know the plan of action and also know it's safe.

2) Supplying a 240 VAC water heater which utilizes a 4500 watt heating elements with 120 VAC is certainly doable, and unless I'm missing something, I'm thinking this should be considered a safe alternative when in a "pinch"?

3) Wiring a 240 VAC water heater in this manner will heat water, but the process will take about 4 times longer. The heating element will basically become an 1125 watt element using approximately 9 amps of current. *Is my thinking correct??*

Again, the likelihood of me ever having to do this is extremely slim, but I do want to have a plan and know it's doable and safe!

Thanks for your input!


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## motormonkey (Jul 10, 2016)

First, it is not code compliant. That does not necessarily mean it is unsafe, if done properly, it just means that an electrical inspector (or an insurance adjuster) would probably have a coronary if he saw it.
Second, it will possibly not work with a water heater with digital electronic controls found in many newer water heaters, which would be expecting 240 vac to work.
If those conditions are not a problem, then, yes, it is definitely doable and reasonably safe, again, if done properly. Not a bad idea. After a few days without a hot shower, I would begin to consider something like that myself.


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## drmerdp (Apr 10, 2018)

As motor monkey suggested, the controller is rated for 240v and probably won’t work with 120v. You can probably find a cheap 120/240 generator to dedicate to the water heater and run the more efficient eu3000 the rest of the time. 

When you replace your current water heater maybe consider gas.


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## Dutchy491 (Sep 18, 2019)

We've experienced several days of no power on several occasions. We had quick/short showers and had enough hot water for three days, although it became luke warm by the third day. That was with generator power only for the water pump and required household items, hot water tank turned off at panel, 3 family members in the house. So not too bad considering.... Dutchy


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## tvl (Nov 14, 2018)

Thanks for the replies!

I seriously doubt I will ever need to do what I was proposing. But, it is good to know I have a plan should I ever get stuck between a rock and hard place!

Thanks again!


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## iowagold (Jan 22, 2020)

well a better plan is to get a small 120vac hot water heater and a watts recirculate pump.
those pumps with the special valves for hot water now.
place the 120 vac hot water heater ahead of the larger 240 vac unit to use the larger tank as storage.
water takes longer to heat on the little heater.
but if you are just lighting a few lights... you will have room on the gen set to run the 120 vac hot water heater.
place the 120vac hot water heater on it own branch with its own dedicated breaker.
and the same for the recirculate pump but add a timer that you can access easy up stairs.

or if you have lp or ng add a second hot water heater for the bi fuel option.
that is what i have done here.
one large electric, one small electric, recirc system, one large NG heaters.
works great for me!
and no dodgy wiring.

gas water heaters work better. more bang for the buck!. but if you cannot get gas at your location..
electric is ok.


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## tabora (Sep 6, 2018)

tvl said:


> Again, the likelihood of me ever having to do this is extremely slim, but I do want to have a plan and know it's doable and safe!


Alternatively, add a 120V water heater to the system. I replaced a 240V 50 gallon water heater in my cottage (to make room for a stacked washer/dryer) with a 120V 7 gallon titanium water heater that can also easily be run off a generator since it has a standard 15A plug. It makes enough hot water for a 10 minute shower or 20 minutes of dish washing (manual or machine). It's our sole source of hot water there 3 seasons of the year. Easy to add to any plumbing environment.










https://www.amazon.com/Bosch-Mini-Tank-Tronic-3000-ES8/dp/B0148O64JE/ref=pd_day0_60_1/147-8405788-6862561?_encoding=UTF8&pd_rd_i=B0148O64JE&pd_rd_r=cd813458-955c-4f0d-a81c-095c86d39c02&pd_rd_w=tPxBx&pd_rd_wg=dycpZ&pf_rd_p=da37a737-19a9-46fa-ac4a-a7e30f9a7dba&pf_rd_r=1SQ19M8XX933D08HX9XK&psc=1&refRID=1SQ19M8XX933D08HX9XK


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## bwswede (Sep 13, 2020)

Interesting idea. Quick question, why does an element go from 4500 watts to 1125 when converting to 120vac?

Blane


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## motormonkey (Jul 10, 2016)

Ohm's law. Volts times amps equals watts.


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## bwswede (Sep 13, 2020)

Thank you for your reply but I still don't follow. I am sure you are correct but I want to know why. Instead of powering it with two 120 volt legs for a total of 240 volts it is being powered with a single 120 volt leg. It seems that the wattage would be cut in half instead of one fourth and the amps would double from 18.75 to 37.5.

Blane


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## motormonkey (Jul 10, 2016)

The resistance of the element will remain the same at about 12.8 ohms. At 240 volts, the current will be 18.75 amps, and power will be 4500 watts. At 120 volts, the current will be 9.375 amps, and power will be 1125 watts.


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## bwswede (Sep 13, 2020)

Thank you!

Blane


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## iowagold (Jan 22, 2020)

and throw in there that it is ac and not dc!
lol!
boom goes my head!!
lol!


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## bwswede (Sep 13, 2020)

Iowagold, that went right over my head. I can't tell if you are giving some kind of warning.

Best,
Blane


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## iowagold (Jan 22, 2020)

engineering ac and dc is a total different thing.
it is over whelming to the normal mind!
you can get brain fried remembering all of the rules different on ac and dc.

basic ac wattage is not linear on hot water heater elements when you change the voltage.
an element has it's sweet spot where it works the best on therms for that element.

you need to get to the "glow sweet spot" for the element to idle or get to the point where the electric element heat exchange is at it's peak efficiency.

you are better off using an element at the correct voltage that it is rated for.
and it is approved for that voltage.

you could change out one of the elements for a 120 vac element...
but in a normal 240 house.
a 240 hot water heater does better on btu to watts used ratio.

but if you only have 120 vac.
use a proper element for the 120 vac.
and the best way to get there is off the shelf made for your voltage water heaters.
and yes multi hot water heaters rock on bi fuel systems!

back up power choices are a good thing.


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## bwswede (Sep 13, 2020)

Got it. Thank you!

Blane


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## Ground Fault (Jun 9, 2020)

We've had quite a few extended periods without power and hot water since the 80's, and if momma don't get a hot shower every other day (and for sure every third day), life is "tenuous" at best. Here is our solution, and we like it better! It's better than the indoor shower: Produces 2-1/2 gallons/minute of unlimited hot water versus only 40 gallons of 1.5 gallons/minute inside water. Can you imagine how luxurious a 2-1/2 gallon/minute shower can be when you aren't worried about how many Kw it is drawing? I pitch it just inside the door of my shop and raise the door an inch or so and the water runs out under the door. I can't get her out of it. My granddog golden retriever lays down in the warm stream and goes to sleep. Best of all, at early-spring crappie camp on Sam Rayburn, set at maximum water temp it produces all the hot steam an weary old angler needs to soak up after a long day out on the water, for as long as you want, to soothe and restore while sitting inside on a five gallon bucket drinking a ZingZang Bloody Mary. Or two. The line forms behind me, and my lineage is colorfully called into question as a take my time...


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## bwswede (Sep 13, 2020)

Nice set up and a nice idea. However, we rarely lose power during warm weather, it is almost always during ice and/or snow. I can guarantee my wife will not go outside to take a shower when the temperature is below 32 regardless how warm it is inside the tent.

Blane


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## Ground Fault (Jun 9, 2020)

Nor will mine. Actually, she won't get in or out of the tent in any season. She only does tents like the one pictured below. She has showered in this though below 32 during an extended period without power due to an ice storm. Once the concrete warmed beneath her feet in the shop she liked it in there. It makes a TON of steam under those conditions! 

















I prefer my hammock, either at crappie camp, or if alone I just stay out on the boat near my crappie brush piles:

















Either way, I am never too far away from the hot water heater and its comfort.


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## iowagold (Jan 22, 2020)

willon said:


> The resistance of the element will remain the same at about 12.8 ohms. At 240 volts, the current will be 18.75 amps, and power will be 4500 watts. Is it true?


in the real world the element current may go down when it heats up or water gets up to closer to temp depending on the metals in the element.
look at this live with your current and voltage meter setup.
and it is different depending on the element style as well as mfg.

i use the stainless elements these days on the electric.

switching to NG soon for hot water as the price on electric water heating is out of control with price of electric going up again.
working on the new pex runs this summer.


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