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  1. #14
    Join Date
    Nov 2008
    Posts
    12
    I don't even have 15 gallons of water combined in the whole system!
    I am tempted to have him replace this one gallon with a 3 gallon.

  2. #15
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,753
    A 15 gallon bladder tank, isn't as big as you may think.

    And there is no harm having a 15 gallon bladder tank on a system that only need 2 or 3 gallons of expansion.

    Keep in mind, that systems that run at low temps during the mild weather, and then at high temps as it gets colder out, have to be figured at teh high temp, not the low temp.


    PS: Do NOT use a portable water expansion tank.
    It does void warranty, as it is not listed for use with that boiler.
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  3. #16
    Join Date
    Nov 2008
    Posts
    12

    How big a bladder?

    portable? or potable?

    Reading my manual, I have an open-type system with a bladder tank and an automatic air vent. The manual also states that I will need a 3 gallon bladder tank at 12psi.

    This tank will hang from the pipes and I cannot see it being 15 gallons.
    Is this how you you install all of your systems, I can understand that too big is better than too small, but my system only needs to release about a cup of water to lower the psi one pound at 150degrees.

  4. #17
    Join Date
    Nov 2006
    Location
    Mechanicsburg, PA
    Posts
    310
    I never heard of a 1 gallon expansion tank. I believe he means a #15. It is about the size of a gallon or two container but is equal to a 15 gallon non-bladder type tank.

  5. #18
    Join Date
    Nov 2008
    Posts
    12

    equal?

    I want to believe that the little #15 tank I have is big enough.

    It doesn't take much water to relieve the pressure in my system even with both zones circulating.

    I could relieve alot of pressure with that little tank.

    What do you guys think?

  6. #19
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,753
    I tend to refer to tank sizes using open/steel tank sizing.
    A #30 tank is what you should have as a minimum size tank.

    A #30 is roughly equivalent to a 15 gallon open/steel tank. In ability.
    They don't hold the same amount of water.

    The tank you have, if it came with 40PSIG of air pressure, its a thermal tank(potable water), not a hydronic expansion tank.
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  7. #20
    Join Date
    Nov 2006
    Location
    Mechanicsburg, PA
    Posts
    310
    Here is a brochure from Extrol for sizing. Use worst case scenerio. Other manufacturers have different charts. I know the tank size changes at different points in the chart.
    http://www.amtrol.com/pdf/extrolbrochure.pdf

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