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Old 05-31-2010, 01:13 PM   #1
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Thermal expansion tank placement


Hello all,

I replaced a gas water heater recently and I know I should add an expansion tank. My question is about where can I/should I put it.

Frankly I would rather not try to put it in the very small utility room- mainly because I would have to relocate the supply line to make room. Another reason is that I have planned for a couple of years, when I get around to it, to go to where my supply line comes in from the utility service and make some changes. I need to re-route my outdoor spigot because it is now under a porch addition and I would like to add a whole-house filter system. If I am going to be opening the line there anyway, why not install the expansion tank where the water service comes in the house instead of at the water heater?

The former water heater tank failed after 6 years of a 9 year warranty and was replaced for full value at Home Depot. Have to give the CS rep the kudos there. A couple of years ago the county water dept replaced all the meters and added anti-siphon valves and I am familiar with how that most likely contributed to the early failure. Service supply is about 70 psi. when they checked the fire hydrants so I will use that as a default value for that purpose.

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Old 05-31-2010, 03:26 PM   #2
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Thermal expansion tank placement


You should put the expansion tank as close to the water heater as possible on the cold side. That tank air should be set to you incomming water pressure before you install it.

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Old 05-31-2010, 08:27 PM   #3
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Thermal expansion tank placement


I don't see anything in the code that prevents it from being installed somewhere else in the system.... MFG requires that it is installed on the cold side (I see a lot of plumbers putting them on hot side )

For example, if you were on a well system, and had a pressure tank on the system, the inspector wouldn't require you to install a second (albeit smaller) expansion tank in the system.

That being said, I would PREFER it be installed at the water heater personally, just for the simple fact that if someone came to work on the water heater, they would not try to install one on the heater.

Installing it on the water heater really isn't that difficult depending on the amount of space you have on top. It's just a matter of a few brass fittings.
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Old 06-01-2010, 01:01 PM   #4
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Thermal expansion tank placement


Alan:>>> MFG requires that it is installed on the cold side (I see a lot of plumbers putting them on hot side<<<

Thats because they keep throwing away that irritating piece of paper that comes with them (i.e. the instructions)

>>>For example, if you were on a well system, and had a pressure tank on the system, the inspector wouldn't require you to install a second (albeit smaller) expansion tank in the system.<<<

Even though that doesn't make sense, there are jusisditions that require expansion tanks on ALL water heaters!

Thats the trouble with codes, you can find 15 different variants in the same state
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Old 06-01-2010, 05:06 PM   #5
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Thermal expansion tank placement


Quote:
Installing it on the water heater really isn't that difficult depending on the amount of space you have on top. It's just a matter of a few brass fittings.
The space in this utility room is tight (4 ft wide and maybe 2 feet on top) but not unbearably so. But if I am going to open the line somewhere else anyway for another project, why not just install it there. In my limited "master of none" knowledge, it seems that the pressure would be the same whether it's 18 inches from the HWH or 30 feet away at the service entrance, as long as it's in the house (on this side of the meter and backflow preventer). Meter is probably 75 feet from the house.

It would take maybe 30 minutes to an hour to do it at the HWH. Just wondered why not somewhere else. BTW- I do know that it goes on the cold side. That's why I was thinking of working it into this other project.

Thanks for the input.
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Old 06-01-2010, 10:23 PM   #6
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Thermal expansion tank placement


Quote:
Originally Posted by braindead View Post
>>>For example, if you were on a well system, and had a pressure tank on the system, the inspector wouldn't require you to install a second (albeit smaller) expansion tank in the system.<<<

Even though that doesn't make sense, there are jusisditions that require expansion tanks on ALL water heaters!

Thats the trouble with codes, you can find 15 different variants in the same state
How does it not make sense? A pressure tank is the same exact device as a thermal expansion tank except that it is much larger.

Quote:
Any water system provided with a check valve, backflow preventer, or any other normally closed device that prevents dissipation of building pressure back into the water main shall be provided with an approved, listed, and adequately sized expansion tank or other approved device having a similar function to control thermal expansion. Such expansion tank or other approved device shall be installed on the building side of the check valve, backflow preventer, or other device and shall be sized and installed in accordance with the manufacturer's recommendation.
The thermal expansion occurs throughout the entire system so it really doesn't matter where you put it. We have even put the watts thermal expansion ballcocks in toilet tanks before, where contractor was too stuck on cramming a small water heater in the back of an understair closet where there was no room for one. I don't really like those, because they waste the water down the drain rather than expanding the system to the accumulating pressure.
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Old 06-02-2010, 08:19 AM   #7
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Thermal expansion tank placement


For safety's sake, although the code might not spell it out, an expansion tank should be between the shutoff valve and the water heater.

Perhaps someone could explain why the expansion tank should not be on the hot side, I don't understand this one.

I would not have expected the lack of an expansion tank to have led to early failure of the heater; the relief valve (temp. & pressure valve) should have let some water out.
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Old 06-02-2010, 09:09 AM   #8
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Thermal expansion tank placement


Quote:
Originally Posted by AllanJ View Post
For safety's sake, although the code might not spell it out, an expansion tank should be between the shutoff valve and the water heater.

Perhaps someone could explain why the expansion tank should not be on the hot side, I don't understand this one.

I would not have expected the lack of an expansion tank to have led to early failure of the heater; the relief valve (temp. & pressure valve) should have let some water out.
Doesn't matter if it's before the valve or after. Think about when you are going to turn that valve off. Only to service the water heater, at which point you'll have power off anyway, and/or supply lines disconnected. This does bring up a good point that wherever you install it (other than water heater location) it would be a great idea to have a shutoff valve and a drain down valve for servicing.

The only reason you shouldn't put it on the hot side is because the manufacturer says to install it on cold water supply only. I'm pretty sure putting it on the hot will void the warranty.

Lack of expansion tank actually should cause premature failure of the tank. What's your T&P valve set at for a pressure setting? It should be 150 PSI if i'm not mistaken, but maybe different brands have different settings... At any rate, that's almost double the max operating pressure for the inside of a home. If thermal expansion is bumping up the pressure to 120, 130, even 140, that T&P is not going to let it out, rather just add stress to the tank.
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Old 06-05-2010, 02:19 PM   #9
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Thermal expansion tank placement


Alan,
I'm not clear on a couple of your points.
Quote:
Lack of expansion tank actually should cause premature failure of the tank.
Is this a typo error? Did you intend to say the that lack of a tank would or would not cause failure?
The history of my original comment is that the first tank lasted over twenty years with a family of six. I replaced it and the second tank only lasted six years with only two adults now. The only thing that changed was the county putting in the new meters with anti-siphon valves on them, which would have prevented the expansion pressure to push back up the supply if I understand this process correctly.

Quote:
If thermal expansion is bumping up the pressure to 120, 130, even 140, that T&P is not going to let it out, rather just add stress to the tank.
I thought the phenomenon of thermal expansion pressure was caused by the tank heating the water and that the purpose of the expansion tank was to absorb this pressure, not add to the problem.
The T&P drains to the outside so I really don't know how much it may have been actuating. Not enough so that there was a puddle or anything.

AllanJ,
Quote:
I would not have expected the lack of an expansion tank to have led to early failure of the heater;
So you're saying that I don't really need an expansion valve? See the above history note.
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Old 06-05-2010, 05:59 PM   #10
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Thermal expansion tank placement


Quote:
Originally Posted by downunder View Post
Alan,
I'm not clear on a couple of your points.

Is this a typo error? Did you intend to say the that lack of a tank would or would not cause failure?
The history of my original comment is that the first tank lasted over twenty years with a family of six. I replaced it and the second tank only lasted six years with only two adults now. The only thing that changed was the county putting in the new meters with anti-siphon valves on them, which would have prevented the expansion pressure to push back up the supply if I understand this process correctly.


I thought the phenomenon of thermal expansion pressure was caused by the tank heating the water and that the purpose of the expansion tank was to absorb this pressure, not add to the problem.
The T&P drains to the outside so I really don't know how much it may have been actuating. Not enough so that there was a puddle or anything.
Not a typo. In that situation with a check valve at the meter, your expansion is going to stay in your system, causing undue stress on the tank.... 6 years is not that great, but I wouldn't expect to buy a new tank nowadays and get another 20 years out of it by any means. I'd estimate 10 at most.

Second point, you are absolutely correct, and that is the point I was making in regards to AllanJ's comment about the T&P letting out some water. It won't do that until it reaches well over what is allowed in a house.

Hope that makes sense.
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Old 06-06-2010, 10:40 AM   #11
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Thermal expansion tank placement


Quote:
Hope that makes sense.
Not yet.

1. I know that the anti-siphon valve at the meter will hold all the pressure on the house side.

2. It is my understanding that the purpose of the thermal expansion tank is to absorb the expansion pressure that is caused by the HWH and is blocked by the A/S valve at the meter from going back out into the county supply system.

3. So if 2 is correct, how does the house pressure get to
Quote:
If thermal expansion is bumping up the pressure to 120, 130, even 140,
with an expansion tank installed? Or am I reading this wrong?

4. I know the T&P doesn't release until 150 psi, which is too much for the house on a regular basis (like high blood pressure), which is why I am considering intalling the thermal expansion tank now that I have learned about the county's change to the meters.

And so my question remains, all rhetoric nothwithstanding, does anyone know of a problem with installing the tank in the crawl space where the water supply comes into the house? Although all of the installs I have seen show the tank very close to the HWH, all the directions I have seen have a generic schematic showing the tank in the system, on the cold side, between the HWH and the meter. Which is exactly where it will be.
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Old 06-06-2010, 10:50 AM   #12
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Thermal expansion tank placement


Quote:
Originally Posted by downunder View Post
Not yet.

1. I know that the anti-siphon valve at the meter will hold all the pressure on the house side.

2. It is my understanding that the purpose of the thermal expansion tank is to absorb the expansion pressure that is caused by the HWH and is blocked by the A/S valve at the meter from going back out into the county supply system.

3. So if 2 is correct, how does the house pressure get to with an expansion tank installed? Or am I reading this wrong?

4. I know the T&P doesn't release until 150 psi, which is too much for the house on a regular basis (like high blood pressure), which is why I am considering intalling the thermal expansion tank now that I have learned about the county's change to the meters.

And so my question remains, all rhetoric nothwithstanding, does anyone know of a problem with installing the tank in the crawl space where the water supply comes into the house? Although all of the installs I have seen show the tank very close to the HWH, all the directions I have seen have a generic schematic showing the tank in the system, on the cold side, between the HWH and the meter. Which is exactly where it will be.
He was saying the T&P would let some water out. I was explaining that it wouldn't, and WITHOUT an expansion tank, it would cause damage to the tank.

Nothing wrong with your location, however as I stated above, I'd definitely put a shutoff valve, and install a boiler drain on the tank side of the valve.
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Old 06-06-2010, 11:28 AM   #13
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Thermal expansion tank placement


Quote:
He was saying the T&P would let some water out. I was explaining that it wouldn't
Yes it does. Which is how I discovered this in the first place. This is a 150 psi, 210* valve.
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Old 06-06-2010, 03:08 PM   #14
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Thermal expansion tank placement


You should never isolate and expansion tank from the vessal it serves, meaning it should be installed on cold water side between valve and heater. installation on hot sides void warrenties due to tank bladders not being rated for hot water and I have seen a lot of tank failures when this is done. Make sure the tank is sized properly for the btu's of the system. All that being said the tank will absorb the pressure from thermal expansion no matter where it is installed in the system untill someone shutts off a valve be it accidental or intentional
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Old 06-06-2010, 03:15 PM   #15
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Thermal expansion tank placement


It can be anywhere in the cold water side. A lot of new meter/backflow sets have it installed right there. Because the manufacturer says install it in the cold piping then the code says the same thing because the code says to do what the manufacturer says.

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