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#33442 - 01/21/04 12:36 AM Water Heaters/ Heat Elements  
aldav53  Offline
Joined: Aug 2001
Posts: 545
Chandler, AZ USA
Do the upper and lower heat elements on a water heater cycle or do both kick on together?
I saw one recently that had 2 taps on the lower element for 2 different wattages. One element on it was open, wonder if I could just move it to the other tap. The good tap had a resistence of about 30 ohms which would probably be to lower wattage on that lower element. It was 2900 watts and 3800 watts I believe on the lower.
The upper element was 3000 watts.

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#33443 - 01/21/04 12:43 AM Re: Water Heaters/ Heat Elements  
straightedge  Offline
Joined: Mar 2002
Posts: 86
Mesa, AZ
I was always under the impression that the upper and lower elements cycle. Never on at the same time.

Usually the upper and the lower elements are rated at the same KW. You only have to figure the amps for one. Because only one will be on at any given time.

#33444 - 01/21/04 12:53 AM Re: Water Heaters/ Heat Elements  
aldav53  Offline
Joined: Aug 2001
Posts: 545
Chandler, AZ USA
I think your right, it seemed to do that when I was checking it.

The Golden Rule - "The man with the gold makes the rule"

#33445 - 01/21/04 01:36 AM Re: Water Heaters/ Heat Elements  
stamcon  Offline
Joined: Mar 2001
Posts: 329
So San Francisco CA
When the temperature of the water in the top area of the tank gets up to the upper thermostat setting, the thermostat shuts off power to the upper element and energizes the lower thermostat/element.


#33446 - 01/21/04 11:52 AM Re: Water Heaters/ Heat Elements  
cpalm1  Offline
Joined: Jan 2004
Posts: 66
and the opposite of what stamcon said is true too. If you are drawing hot water, the lower element will kick on first. if you start to run low, the upper element turns on and shuts off the lower element at the same time.

How does this work?
the upper element basically has a 3 way switch in it's thermostat. when the upper element is off, the switch is in the position to allow power to the lower element. If the lower element wants to turn on, it can. when the upper element turns on, it's switch flips, sending power to the upper element only, regardless of what the lower element wants.

Why have two elements if only one can run at a time?

this is for faster recovery time. since the upper element is only heating about 1/3 of the tank, you will have hot water faster than if there was only a bottom element.

Why can only one run at a time?

Because thats how they come hooked up. If you only have 100 amp service, two elements running at a time may not leave enough power for an oven, stove, and dryer.

If you have 200 amp service, you can rewire the heater so there are two breakers going to it, one for each element. That is what i did on the heater at my vacation cabin. I needed fast recovery times, because I turn off the heater when i am not there. when i go up for vacation, i want hot water FAST, and two 4500 watt elements gets the job done amazingly well, especially considering the well water is only 40 degrees. the 50 gallon tank is heated to 150 degrees in about 2 hours and i have warm water in less than 10 minutes. Of course, when im also running the baseboard heat and oven, the electric meter looks like it is going to blow up [Linked Image]

I have never seen an element with dual wattage settings, but my theory is the 3800 watt setting is for 12 AWG wire and the 2900 watt setting is for 14 AWG wire. 2900 watts at 240 V is exactly 12 amps, which is the maximum continuous load on a 15 amp circuit (3 hour rule, don't know code reference). don't tell anyone, but I only have 12 AWG wire going to my 4500 watt (18.75 amp) heater [Linked Image] maybe i'll fix it if i have time, but it's worked fine for the last 60 years

[This message has been edited by cpalm1 (edited 01-21-2004).]

#33447 - 01/21/04 12:14 PM Re: Water Heaters/ Heat Elements  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
the 50 gallon tank is heated to 150 degrees in about 2 hours

Setting the water temperature that high is very dangerous. Look at the following quote from this Univerisity of Missouri document
Water heaters leave the factory set at 140 to 150 degrees Fahrenheit. It takes 2 seconds for a child to receive third degree burns from water at 150 degrees. It takes 5 seconds if the water is at 140 degrees, and 30 seconds at 130 degrees.

From an Australian Governmenent Health document
60°C major burn in 1 second
55°C major burn in 10 seconds
50°C major burn in 5 minutes

Note that 150°F is equal to 65.5°C.

[This message has been edited by resqcapt19 (edited 01-21-2004).]


#33448 - 01/21/04 06:44 PM Re: Water Heaters/ Heat Elements  
aldav53  Offline
Joined: Aug 2001
Posts: 545
Chandler, AZ USA
I think what cpalm1 is doing is ok. (except maybe for the wire size). You can set the temp at whatever you want, it just gets there faster.
150 deg is 150 deg, right?

The Golden Rule - "The man with the gold makes the rule"

#33449 - 01/21/04 07:45 PM Re: Water Heaters/ Heat Elements  
Attic Rat  Offline
Joined: Dec 2003
Posts: 524
Bergen Co.,N.J. USA
..Dopey question....
..if you put the water heaters t-stat up higher, and you have a pressure; everytime the downstairs tenant turns on her shower WHILE you're in yours,and you get freezing water showered on you,..will turning up the t-stat cure this?? my rationale sez "if the water temp is hotter, you'll use less of it, and the hot water to cold water ratio would be different....??? or if the tank empties quicker than usual,..or am I off my rocker?? there something out there to compensate for this phenomenonenonenem????

.."if it ain't fixed,don't break a Licensed Electrician"

#33450 - 01/21/04 08:02 PM Re: Water Heaters/ Heat Elements  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I have run into a water heater rewired to run both elements, the people told me they wanted faster recovery times also.

I was at their house to rewire the home to the point the AHJ would allow the POCO to turn the service back on.

They had an electrical fire in another part of the house from their handy work.

I found the jury rigged water heater when I found the 30 amp fuses for it wrapped with tin foil.

Once I opened the water heater I found most of the factory wires insulation melted.

So cpalm1 a couple of questions what size breaker are you running, what size conductors for the branch circuit and did you replace the factory wires that now carry twice the current intended?

AR, You can get a little gizmo I think it is called a temptrol to do what you are talking about.

My hot water heater is a tank-less in my steam boiler it puts out water at 190 F and this device mixes that 190 F water with cold to keep the usable water at 120 F.

This is also a benefit as the tank-less can not supply that many GPM.

Bob Badger
Construction & Maintenance Electrician

#33451 - 01/21/04 09:19 PM Re: Water Heaters/ Heat Elements  
frenchelectrican  Offline
Joined: Feb 2003
Posts: 939
Wi/ Paris France { France for ...
aldav53 the tap you been descrbinng some case it have dual wattage but bear in mind most waterheater will have the wattage stamped on the element. the first one [higher side ] useally rated for 240 volts system and the second rating is for 208 volts system so recheck the rating on the element there.

one of my old home ihave before i have hot water heating system and i have heat exchanger on it. my boiler was dailed in at 175 most of the time but have blending valve to keep the domstaic hot water for sink and tub and keep the temp at 115 degrees to prevent burn etc ..

merci , marc

Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)

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