Where to begin with expansion tank

Discussion in 'Water Heater Forum, Tanks' started by Bob from accounting, Apr 29, 2020.

  1. Bob from accounting

    Bob from accounting Member

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    Mar 5, 2020
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    California
    So jumping right in here,
    Any preferred resources you can point me to to learn more about expansion tanks.

    I will be updating my plumbing and it was suggested to install an expansion tank. If it matters my Water heater I think is a Rheem 40 gallon tank?
    Looking at expansion tanks to install, I see there are many sizes, products. materials, shapes and types?

    Is there a beginners guide here to figure out the direction I should consider with picking one out?

    Hoping this solves water hammering, thermal expansion and maybe relieves some water shock on the resin of a water softer down stream?

    Thanks for any advice and resources.
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Pick a company, go their website, and put in your parameters and it will recommend a properly sized ET. Here's one http://tools.watts.com/ETP/
     
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  4. LLigetfa

    LLigetfa DIYer, not in the trades

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    Surely not downstream of a water heater? You must mean upstream?
     
  5. Bob from accounting

    Bob from accounting Member

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    I think my relif valve is 150 psi but not totally sure? Hard for me to tell the temperatures also?
     

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  6. Bannerman

    Bannerman Well-Known Member

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  7. Bob from accounting

    Bob from accounting Member

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    Can I caution on the side of oversizing it being the cost difference is minimal? I probably will simply go with a 2 gallon tank here, but what happens if I went with a 4 gallon tank, especially if they cost the same, what are the draw backs to doing that? Again, I will go with a 2 gallon tank, but hypothetically, what are the cons of oversizing your expansion tank?
     
  8. Reach4

    Reach4 Well-Known Member

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    Other than the space and mechanically supporting the heavier tank if it fails, and becomes full of water, no disadvantage.
     
  9. fitter30

    fitter30 Active Member

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    Expansion tanks sized 1% of total capacity 3/4" pipe .023 gallon foot 150' 3.2 gallon
     
  10. Bob from accounting

    Bob from accounting Member

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    Does the Expansion tank need to be mounted on or near the Water Heater inlet. Can I mount the tank 5' away on a more accessible area of the incoming line? Or does that defeat the purpose? My pipes are not behind any walls so I have more space in another room, prior to the WH closet.
     
  11. Bannerman

    Bannerman Well-Known Member

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    Location:
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    The expansion tank provides space to absorb the expansion of cold water as it is heated in the water heater. The Xtank could technically be located anywhere there is a cold water line in your home as long as there is not a check valve or other back flow prevention device located between the water heater and the Xtank.

    Since there is a water softener, it would be best to locate the Xtank between the softener and WH. If the Xtank is upstream from the softener, the expanding and condensing water will move back and forth through the softener which can result in the softener's flow meter detecting flow when no water is actually being used.

    Your 5' away location should be fine assuming it is downstream from the softener.​
     
  12. Reach4

    Reach4 Well-Known Member

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    delete
     
    Last edited: May 4, 2020
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Retired Systems engineer for defense industry.
    Location:
    New England
    Ideally, you don't want a shutoff between the ET and the WH to ensure it can always do its job. But, if the line is unobstructed by a valve of some sorts, it doesn't really matter, the pressure will rise everywhere in your system that isn't protected by a valve.
     
  14. Bob from accounting

    Bob from accounting Member

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    Thanks for the helpful advice. I will mount this between the Water Softener and WH. I will have a typical shut off valve on the water heater. So there will indeed be an open, shut off valve between the XTank and WH. Can you "expand" upon why this is not ideal to have a shut off valve down stream of the X? Technically I will have shut off for the Water Softener to which is upstream of the XTanks. Please do explain your thoughts on shut off valves, xpansion tanks "to do their thing."
    I will note that almost every photo of Expansion tanks on the net show the tank mounted right next to the WH if not right on top of it, they are mounted downstream of the WH shutoff just like you are saying. This had me believing it had to be done this way?
     
  15. Bannerman

    Bannerman Well-Known Member

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    Location:
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    Unless there is a problem with the WH or hot water plumbing system, the shut-off valve on the cold feed to the water heater will remain fully open when the WH is in use. A fully open valve will not isolate the WH from the X-tank even if the X-tank is located before the shut-off valve.

    If there is a valve located between the X-tank and WH that is likely to be closed, then that valve will isolate the 2 devices from each other, so the X-tank would then not be able to absorb the expansion from the WH.

    Since the X-tank's main purpose is to absorb the expansion caused within the WH, it makes sense to locate the X-tank as close as possible to the source of expansion, but that is not always possible. As stated earlier, the X-tank could be connected to a cold line anywhere within the home, and it will still function correctly, as long as no backflow prevention devices or closed valves are located between the two devices.

    When the home's water source is a private well, an expansion tank is usually not needed since the well pump's pressure tank will absorb the expansion from the WH.

    Prior to my town installing water meters with integral check valves, most homes did not need an X-tank as the expansion from each WH was absorbed by the municipal distribution system. Once the meter and check-valve were installed where the water service entered each home, water could no longer flow back into the distribution system so the town also installed X-tanks in every home. Those expansion tanks were often located remotely from the WH depending on space availability.
     
    Last edited: May 4, 2020
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