Thermal Expansion Tank

Discussion in 'Water Heater Forum, Tanks' started by tvl, Jan 5, 2014.

  1. tvl

    tvl New Member

    Messages:
    138
    Location:
    South Carolina
    I have a couple of dumb questions, but i do need the answers:

    I am about to replace our old 40 gallon water heater. The old setup does NOT utilize a thermal exapnsion tank:

    1- Does it matter which water line I have the thermal expansion tank soldered on. The cold water line is more easily accessible, but I've got a feeling it should be on the hot water line ...................... or does it really matter?

    2- What size tank shoud be used for a 40 gallon water heater ........ city water - about 50 PSI pressure

    Thanks so much!
  2. nukeman

    nukeman Nuclear Engineer

    Messages:
    709
    Location:
    VA
    You only need one if you have a closed system. For instance, if you have a Pressure Reducing Valve (PRV) or a check valve in the water meter. If you don't have a closed system, the expansion tank won't be needed.
  3. Terry

    Terry Administrator Staff Member

    Messages:
    14,819
    Location:
    Bothell, Washington
    If you install an expansion tank, it should be on the cold side. A 2.2 gallon is fine.
  4. tvl

    tvl New Member

    Messages:
    138
    Location:
    South Carolina
    Thanks to both of you!!

    It is a closed system and I will use a 2.2 gallon on the cold water line. Does the thermal expansion tank need to be mounted within a certain distance from the water heater??

    Thanks again!
    Last edited: Jan 5, 2014
  5. Terry

    Terry Administrator Staff Member

    Messages:
    14,819
    Location:
    Bothell, Washington
    It can be anywhere in the system. I have mine near my garage door on the incoming cold, not near the water heater.

    [​IMG]

    This one is in a customers home.
    New PRV, shutoff and added an expansion tank.
    Last edited: Jan 6, 2014
  6. tvl

    tvl New Member

    Messages:
    138
    Location:
    South Carolina
    And Terry, are the big box expansion tanks OK ......... or better to go elsewhere?
    Last edited: Jan 5, 2014
  7. Terry

    Terry Administrator Staff Member

    Messages:
    14,819
    Location:
    Bothell, Washington
    Same stuff. It's hard to mess up the expansion tanks.

    I went skiing yesterday and I noticed our friends had replaced a kitchen faucet in their condo. He had picked up an "opened" box Delta faucet and installed it. There was a problem with it, so he wound up replacing it. Someone else had returned it, and it had been put on the shelf and sold to him. He had picked up somebody else's return.
    It's a 70 mile drive to his condo up in the mountains. :(
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,834
    Location:
    New England
    FWIW, the expansion tank is supposed to be on the cold side as said, and anywhere is okay, BUT, it is supposed to not have a valve between it and the tank. The water will expand everywhere in the closed system and those designed for potable water (not the heating/boiler ones) are only designed for cold water, not hot.
  9. tvl

    tvl New Member

    Messages:
    138
    Location:
    South Carolina
    Terry,

    Thanks for posting the photo ................ I do like the way that one is installed. It has given me another idea as to where to install it.

    Question: Do these tanks need to be checked periodically to ensure the air charge is correct? If so, then I need to install it so that it is easily accessible.

    Thanks again!
  10. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,315
    Location:
    Cave Creek, Arizona
    quote; those designed for potable water (not the heating/boiler ones) are only designed for cold water, not hot.

    Domestic water "expansion tanks" are glass lined and will work for cold OR HOT water, (in fact the way they operate means that "hot water" will seldom even enter the tank and NEVER reach the rubber diaphragm). Heating tanks are black steel and will corrode if used for domestic water purposes.
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