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Does anyone know how to calculate steam Lbs/Hr?

Ken Sappio
Ken Sappio Member Posts: 16
I am still not understanding, is it Lbs of water or Lbs of steam concerning a boilers rating? And again, is it Lbs of water or Lbs of steam when talking about traps?


  • Ken Sappio
    Ken Sappio Member Posts: 16
    Does anyone know how to calculate steam Lbs/Hr?

    When a boiler is rated in Lbs/Hr what does that mean?

    Is it the Lbs of water it will convert to steam in 1 hour or is it the Lbs of steam itself it will generate. I quess what I am asking is it water or steam?

    And what about condensate, when a device like a trap is rated in Lbs/Hr what are they talking about, Lbs of steam or Lbs of water?

    Please help.

  • bobbyg_17
    bobbyg_17 Member Posts: 9

    I never thought of it that way. I guess steam is really water in a different phase - when it "releases some of its heat" it becomes water (condensate) again.

    I always look at the conversion factors in Dan's "The Golden Rules of Hydronic Heating"

    I just looked, it actually states, "lbs. of condensate per hour" in his book.

    Hope this helps!
  • Bruce_29
    Bruce_29 Member Posts: 9

    Generally if will mean PPH of steam from and at 212F at 0 psig. If the boiler pressure is above 0 psig, which it should be, then some of the energy will be required to raise the temperature of the water above 212F.
    From and at 212F you can produce 34.5 PPH of steam per Boiler HP (BHP)
    Note:to get say 1000 PPH of steam out you need to put in 1000 PPH of water! Since you usually talk about gpm to the boiler, a rule of thumb is divide the number of PPH of steam out by 500 and that is the number of gpm you need to put into the boiler. 1000 PPH steam/500 = 2 gpm into the boiler.
    If the feed water temperature is less than 212F and the pressure is above 0 psig then the number of PPH of steam you can produce per boiler HP is less than 34.5 PPH
    If your feedwater temperature is above 212F you can produce more than 34.5 PPH/BHP still at 0 psig.
    That's not a full explanation, but it's a start.
    There is a chart in the Cleaver Brooks boiler manual you can use to determine the actual PPH of steam produced at various feedwater temperatures and boiler pressure per BHP.

    For a steam trap it is simply the number of PPH of condensate the trap will pass at a given pressure drop accross the trap. Usually with the condensate at 10 degrees below saturation temperature.
  • Kevin Jahn
    Kevin Jahn Member Posts: 18

    A pound of water is one pound of steam
  • Like Bruce Says,

    A given amount of steam vapor, that is condensed to water will pass through A steam trap depending on the differential between its inlet & outlet.
    This difference between the two in a working trap(vapor & water), is expressed in lbs. per hr. that returns(if uninterrupted) to the boiler.
    The boilers ability to convert water into steam-vapor is dependant on its firing rate, steam chest capacity-size(header included), complete EDR it must satisfy, and the condensate return rate.(Again PPH)
    Hope this helps ;-)

  • bob_46
    bob_46 Member Posts: 813

    I think you MAY be confusing weight and pressure. When a boiler is rated at Lbs./Hr. they are talking about the weight of the water converted to steam in one hour. They are not talking about the pressure in the boiler,which you measure with a gauge.
    One pound of steam (by weight, not pressure) weighs the same as one pound of condensate which weighs the same as one pound of water. (i'm not sure how else to say this. i hope i don't sound like a smart ****)
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