Water heater elements

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Other then taking longer to heat up the water, does any one know of any problems that would result from replacing the heating elements in a tank water lower wattage ones?
I ask because my tank has 4700 watt elements, and the generator I know have wired for emergency use is a 4500 watt unit. (No, I didn't screw up. I've had it for several years, but never had it set up w/transfer switch, etc.) It was suggested that going to 3000 or so watt elements would not cause any trouble, and allow the heating of water when on the generator.
Thanks.
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Retiredff wrote:

Hmmm...guess that should be 'a hot water tank with lower wattage ones'.
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Your HWH is 220 right, what does it pull at 220 Your gen is rated 4500w @ 110. am I missing something or is there a large missmatch
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Watts are watts, voltge does not matter. Higher voltage just means lower amps for the same watts.

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You can but you will lower the recovery time of the heater. You might not be happy running your electric hot wayer heater from a generator. It will burn a lot of gas and you will not be able to run much else while it is running. Do you have a chronic problem with the power going out? What about a very small aux hot water heater just on one bath room?

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Lawrence James wrote:

Recovery time I'm aware of. After testing the set-up, I know how much, and what I can run. The only thing missing is the hot water, in enough quantity for three quick showers (two adults/ one kid).
I have a nine hour run time for the generator, so the a couple hours devoted to hot water is no problem.
Chronic power outages? Well, enough that we are tired of it. In the last four years, more then the previous 20-25 combined. A huge number of our neighbors bought them because of problems this year. At least I've had mine, and it was bought for use away from available power.
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Couple questions raised. First, does y our generator have a 220 volt tap? If not, you're going to be unable to power your W.H.
If the WH will take elements with smaller rating, I'd suggest changing them both. There should be an interlock which allows one or the other element to be running.
It will take a LOT of gasoline to heat the water, though. I don't remember the numbers off hand, but the concept is that a galon of gasoline produces some number of watts (for one hour).
If you use your generator to run your natural gas furnace, your gasoline lasts a lot longer. Cause the gasoline isnt the only energy source.
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What is allot, Chris? A typical 40 gallon electric heater has a recovery of about 18 gallons per hour, lets just round it to 20 gallons per. At that rate it will take two hours to heat the tank. A 4500 watt gennerator running full load takes a bit more than 1 gallon per hour, so 2+ gallons. Greg
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What I did awhile ago was to go to my Norther Hydraulic catalog, and look at the generators. I did some math. They said what was the wattage of the generators, and how many galons they held, and how long they ran at half load.
Unfortunately, I can't remebmer the number I got!
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3000, 4000 w apx 1/2 gph - 1. gph depending on unit
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alt-hvac Moderated wrote:

220 already wired to the house. Run time is not a concern (nine hours on one tank) for being able to take the occasional warm shower. If the power is out, you sit around with nothing. If it takes a couple/few hours to warm up the water, no problem. And, I was going to change both elements, not just one.
Heat will not be provided by the generator, as we are on a heat pump. No gas to be had for anything, other then a gas grill.
Your comment about X amount of gas to produce X watts is interesting. I'll need to see what I can find, just for curiosity's sake.
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Retiredff wrote:

Forget it, in an emergency, you will have hot water for a while, but heating a 40-50 gallon tank doesn't make sense. You would heat small amounts of water like 2-3 gallons max probably with a propane burner.
Is your emergency generator 120 or 240 V. If it's 120 V, then it won't power your water heater anyway. Your generator should be used only for lights, refrigeration, electronics, and maybe a tiny bit of heat.
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Actually, it _will_. My inlaws somehow managed to have their 240V WH operating on 120V. Worked fine, but the recovery time was very long. They managed to make do for _years_ (with three daughters no less ;-), thinking that only being able to do one shower every couple of hours was "normal".
The reaction when I fixed it was gratifying to say the least ;-)
If anything, if the OP _HAS_ to run his WH off his generator, rather than swap the elements (and suffer slower response times when the grid power is available), rig it so that when you run the WH off the generator, you're running it at 120V. Current draw will be half that at 240V, and recovery time will be long, but only when on generator.
Thus, a single 15A circuit off the generator will be enough. Leaving 3000W for other purposes.
Going on the opposite direction, ran into an accidentally miswired 120V WH heater on 240V. The elements survived for several weeks. To everyone's amazement...

I think resistive heating off a generator this small is a waste. Particularly for water. Even a coleman stove is a better idea.
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Chris Lewis wrote:

Very few people HAVE to ;), but the set up is done, and the hot water is the only thing missing.
I thought about the slower recovery time, but after 4+ years in this house, with three people, and never having run out of hot water, I figured, at the most, only slight changes in our day-to-day use would be needed, if at all.
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George E. Cawthon wrote:

It is 240. Already set up and tested to see what I can run. I know I can heat up small amounts in the microwave or on my gas grill. Just wanted to find out any downside to trying to get the occasional warm shower for a family of three.
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Retiredff wrote:

You can do a lot better. RVs often have a 5 gallon or less water heater that work fines for showers and they are economical users of gas. We don't take showers in our travel trailer but we do all kinds of body washing, dish washing, etc. Other's that do take showers seem to have no problem. As long as the temperature is above 40 degrees, its amazing how well the tank holds heat and how little propane is used. Retrofitting a small propane water heater might be more work that necessary. But hey, you could just put it in the yard and make everybody take showers outside and it would be hot, not just warm.
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If your generator, etc, is hooked up for 240, then have at it.
My calculations from my Northern catalog went something like:
catalog says "This 10,000 watt generator will run at half power for eight hours on a 5 galon tank"
The math went something like 5KW x 8 hours = 40 KW-H
40 KW-H/5 gal = 8 KW per galon.
Of course, I'm making up numbers to illustrate. But it gives you an idea how much gas you need to keep things going.
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Well stormin he has a 4500 watt unit and wants to pull 3000, a 4500 watt unit is more effecient in itself, less mass to move than a 10000w. and he needs 3000 not 5000 40% less . A good guess is 1/2 gal per hr, not 1gph
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You know, if this is really a problem, you might be better off figuring out how to heat the water off the natural exhaust heat of the generator. Maybe run a small motor to circulate water thru a coil around the exhaust, or if a radiator exists, thru that.

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This is Turtle.
You can drop the wattage all you want as long as you keep the same voltage rating of the elements of the tank pair. The reason i say this in some configurations it can draw too much for the element to stay at the rating of it. the element is rated at the voltage stated on it and say you put a 2,000 watt rated 120 volt element in it and put 220 volts to it. You could have a 5,000 watt element , but you really would not know till you read what it was drawing when you did it. In 120 volt elements i have seen down to 1,200 watts and in 220 volt elements down to 2,500 watts. They could have smaller but i have not seen them.
Now if your going to run a hot water tank on a generator. You must look at the Continuous full load rating of the generator and not the Surge load rating. A 6,000 watt full load rated generator can run at say 7,000 watts for a few minutes and not hurt anything but your over watt protection may pop. So look at the Full load Continuous load rating for continuous operation.
TURTLE
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