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.

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.

I think your right, it seemed to do that when I was checking it.

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.

steve

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


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 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).]

cpalm1,
Setting the water temperature that high is very dangerous. Look at the following quote from this Univerisity of Missouri document
From an Australian Governmenent Health document
Note that 150°F is equal to 65.5°C.
Don



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

resqcapt19,
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?

..Dopey question....
..if you put the water heaters t-stat up higher, and you have a pressure problem..ie; 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??
..is there something out there to compensate for this phenomenonenonenem????
AR

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.

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

"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? "

breakers are 20 amp 240V. This is what the electrician installed when the house was upgraded from 60 amp to 200 amp service 15 years ago. before the upgrade, the heater had it's own meter and a timeclock so it would only run at night. the wiring that goes from the panel to the heater is two 12-2 NM cables, one cable for each element. they are the old style NM that is coated with asphalt/fiber braid, but the actual conductors have plastic insulation. The are in good condition. (i will be replacing them though when i move the heater to the basement from the first floor.) the NM cable goes into a juntion box that is built in to the heater. Individual wires go from there to each element (factory wiring was used for upper element, new wiring for lower).

As for the temperature, it is actually 140. i hit the 5 by mistake. i know that is very hot, but it needs to be that way because the cold water is so cooooooooold. with the water at 140, you still have to open the hot water 3 turns and the cold water 1/4 of a turn when taking a shower. if the hot water was any colder it would be used up too quickly. The side benefit is that you can make hot chocolate with the tap water, no microwaving required

There are double-element non-simultaneous and double-element simultaneous-operation models.
http://www.rheem.com/includes/resourceLibraryPDF/1312.pdf

I would think that the heater would have to be clearly labeled as simultaneous if so intended, to preserve NRTL listing/labeling.

Attic, you will still get a temperature change at the shower. The hotter setting on the water heater just gives you a higher reserve of hot water. When you take a shower, you mix cold water with the hot, so with a hotter heater setting, you would be mixing more cold when using the shower and using less hot water.

What is the temperature rating of the conductors in the old Romex that supplies the water heater?
140°F = 60°C, the temp rating of type TW wire.
Setting the thermostat above that temp would subject the conductors to a temperature above the insulation's rating.
(It seems to me that some of the older, cloth covered romex was only rated at 40°C, but that's only from memory.)...S

It's fine to set your water heater at 150º as long as you have a mixing valve to keep "delivered water" around 120 or less.

And most residential water heaters use one element at a time. Top element has priority and locks ut bottom element until the top of the tank is up to temp.

Most commercial electric water heaters can have all elements on at the same time. Usually ach element is on a different phase.