Water Heater shut-off

My home has two 40 gallon gas-heated water heaters and since we figured we need just one for our needs, I shut-off gas supply to one of the heaters (should save on gas bills). Since the 2 heaters are in "tandem", they have a copper pipe for transferring water from one tank to the other. I checked the plumbing around both tanks and it impossible for me to figure out which tank supplies hot water first before it 'reaches in' to the other tank.
So now, I am at a loss to figure out if I had turned off the right tank. What if I turned off the "primary" tank, in which case, I would end up getting water from the secondary tank that is mixed in with cold water from the "primary tank". This would really make it worse since the water I would get out of the faucets would always be 'tempered' with cold water from the tank that I shut-off.
I thought about this for a while and figured that if I shut-off water supply to (cold, pre-heated water) the tank that I cut the gas supply to, then I would not have the aforementioned issue. I looked for a water shut-off valve, but all I could find was a small, green-colored valve that turns only 90 degrees - open or close, on a pipe that goes into the tank. This pipe is going in to the tank just above where the pilot knob is (the water heater is made by Reliance).
So, my question is: is the small, green-colored valve the right water shut-off valve to cut-off water to the tank? This valve is not something you can rotate - it is a simple, open/close type that only turns 90 degrees.
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Known as ball valves since a ball inside rotates to control flow. The position of the handle indicates if the valve is open for flow or closed to block it.
Depending on your water use, the savings may be minimal. Actually, the only savings is the amount of fuel needed to maintain the temperature at the set point. If you use 10 gallons of hot water, you need a certain amount of energy to heat the incoming water to the set point. It does not matter very much if it is being done in one unit or two.
When no water is being used, the heat from the water is radiating into the space around it. Eventually it has to be made up and the burner will fire. This is actually helping to heat your house, it is not lost, except in summer when you don't want heat.
Try your way, but you may be disappointed at any "savings" you will see. That said, in my last house we had a 40 gallon heater with a family of four and it was sufficient.
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wrote:

turned the power off to my 40 gallon water heater prior to leaving for work. Then, 4 1/2 days later I came home to find I could take a "warm" shower by using JUST the hot water left in the tank.. (well.. lets just say it wasn't cold...) This being an apartment, it wasn't a high tech, super insulated water heater.. but was relatively new. I figure I saved very little by turning power off to unit... I may have saved a little had I turned power off prior to taking my last shower before leaving for work.. so I would have been storing cold water.. Chuck (in SC)
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Thanks for your reply. I agree with you that one tank should be enough - its just two of us in the house.
I managed to find the owners manual and this is what I found:
the gree-colored valve is NOT the inlet water valve as I thought. It is the manual gas shut-ff valve to the heater. So, what I shut off was the main gas supply to the heater (in addition to setting the gas control knob to the "off" position at the thermostat).
So, now I looked for the "Inlet water shut-off valve" so I can turn off water to the heater that I don't want to use. But doggone it, I just cannot find an inlet water pipe at all. What the..! How can my heater not have an inlet water pipe? Puzzling! I sure am missing something. All I see are copper pipes going out from both heaters (which are warm to the touch, telling me they are "outlet" water pipes, not "inlet" and anothet piece of "n" shaped copper tubing that connects both heaters (tandem)).
Where do I find the darn inlet water pipe and its shut-off valve?
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On 26 Dec 2005 11:28:19 -0800, snipped-for-privacy@yahoo.com wrote:

Rather than a water heater, you probably have a water generator.
These are mor e expensive to purchase, but since it came with the house, that is not a problem.
They are also more expensive to run, so you need to compare the running costs with the cost of purchasing water from the utility company. There should be a price per gallon on the water bill, and a KwH per gallon on a plate on the water generator. Along with the model number etc.
If the water in your area is especially expensive, and electricity is normal priced or lower, you may want to turn off your other unit, the water heater, and rely exclusively on the water generator.

Remove NOPSAM to email me. Please let me know if you have posted also.
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I'm puzzled. You can't figure out which pipe is cold water and which is hot? Look on top of the tanks; there probably is a H and C stamped on them. Run hot water and feel the pipes. It should become clear which pipe is feeding cold water.
From your description of the location of the valve, ("just above where the pilot knob is"), it sounds like you are looking at a gas valve, not a water valve.
When you say 'in tandem', do you mean in parallel (cold water feeds both tanks simultaneously) or in series (hot water from 1st tank flows into 2nd tank and then from 2nd tank to faucet.) The way you pose your query makes it unclear which you mean.
If they are in series, you are not getting any mixing. Either the working tank gets unheated water from the first tank, (at the same temperature as if you had only one tank) which it then heats up, or it serves as a storage tank of hot water it received from the working tank. Since you have enough hot water with only one tank, the working tank should be the one closest to the faucets.
snipped-for-privacy@yahoo.com wrote:

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If water goes from one tank to the next leave the water on, the first tank will temper incomming water reducing your bill if it is in a heated area. Most gas tanks have an energy factor of only around 65, tankless gas start at 82 and go to 90+ energy factor. I use my old tank as a tempering tank before the Ng tankless, My furnace is 94% efficient a higher efficiency than most any residential tank so it is tempered up in temp cheaper. My summer gas bills are apx 6-8$ at 1.50 a therm, savings are 25$ a month going from electric. You will feel the pipes to find what is hot.
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You need to work out if the tanks are in series or parrallel.
If they are in series the Hot out of the first goes to the Cold inlet of the second. The seconds Hot outlet goes to the hot water pipe feeding the faucets.
Get a piece of paper and draw up a diagram of the pipework.
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snipped-for-privacy@yahoo.com wrote:

Ok, the two water heaters are in SERIES. There is no separate water shut-off valve to the heaters. If I have to shut-off water to one or both of them, I have no choice but to shut-off water to the entire home. So, I now discard the idea to shut--off water to the heater I am not using.
So here is the current scenario: * I turned off the gas supply to the first tank. I also switched it off by turning the gas control knob to the "off"position. *The first water heater is now acting as a storage tank for incoming cold water. * The second water heater is running and is set to 120 F; it gets cold water from the first water heater * The second water heater is feeding the faucets (outgoing hot water)
So, I think I will save on gas because.....40 gallons of water in the first water heater does NOT have to be maintained at 120 F.
Right?
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You should save a little gas since only 1 tank will be letting hot water cool off to the atmosphere. How much you save will depend on how well the tanks are insulated and how long hot water sits in the tanks before being used. If the tanks are fairly new, (i.e., well insulated), I wouldn't expect to see substantial savings.
What you seem to forget is that when both tanks were working, the 2nd didn't need to use much gas because it was already getting hot water from the 1st tank.
If you need extra hot water for guests, just turn up the thermostat on the working tank.
snipped-for-privacy@yahoo.com wrote:

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When I turned off the first water heater, I noticed that I am NOT getting hot water from the second tank. As I mentioned in my previous post, the 2 water tanks are connected in series.
I am getting luke warm water, at best. So I tried setting the temp control on the second tank to 150 F, but still, I don't get anything more than luke warm water.
Why is this?
I though I would save some gas by turning off the first tank.
TIA.
Bennett Price wrote:

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Do you know for a fact that the second, working, heater is working? Is the pilot lit, does the burner fire? Has the Off/Pilot/On knob been turned to On?
Are you certain that the plumbing is as you described?
Is the cold water going into the 2nd tank going into the opening marked C and is the 'hot water' coming from the H opening? The C opening has a tube inside the tank that sends the cold water to the bottom of the tank (where the burner is) while the H opening is at the top of the tank (since hot water rises).
It is possible that these C and H markings have been reversed; that the dip tube has been moved to the H side of the tank, perhaps to facilitate the plumbing (water and gas).
snipped-for-privacy@yahoo.com wrote:

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snipped-for-privacy@yahoo.com wrote:

Ok, the two water heaters are in SERIES. There is no separate water shut-off valve to the heaters. If I have to shut-off water to one or both of them, I have no choice but to shut-off water to the entire home. So, I now discard the idea to shut--off water to the heater I am not using.
So here is the current scenario: * I turned off the gas supply to the first tank. I also switched it off by turning the gas control knob to the "off"position. *The first water heater is now acting as a storage tank for incoming cold water. * The second water heater is running and is set to 120 F; it gets cold water from the first water heater * The second water heater is feeding the faucets (outgoing hot water)
So, I think I will save on gas because.....40 gallons of water in the first water heater does NOT have to be maintained at 120 F.
Right?
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