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Hot water boiler help

Jake_4 Member Posts: 3
I have a large three story building with about 16 hot water radiators on each floor. The cold pressure at the pump gauges are 10 psi and on the boiler combo gauges it reads 15 psi. I just replaced the bladder in the exp. tank and charged it at 15 psi. The relief valve is 30 psi. The reliefs were popping and I replaced the fill valve and bladder and I have the following questions:

(1) What is the static cold pressure for a three story building? I figured Height divided by 2.31=15 psi? Should I crank up the cold static temp?

(2) The owner says he needs 20-25 psi (at the boiler) at 180 degrees in his system to reach heat to the upper floors. How do you figure system pressure requirements to ensure their is enough water to reach the upper floor at 180 degrees? How does this number work with the static temp? I ran the pumps today with the boiler cold and at 15 psi static the discharge was 22 psi.

(3) Is my relief valve under sized for my required system pressure?


  • Big Ed_3
    Big Ed_3 Member Posts: 170

    If you can bleed water from the upper most radiator , you have enough pressure .

    If the relief pops on temperature rise , then you don't have enough expansion tank .

    If it is a constant drip , then water is feeding into the boiler.

    If it releases when a circulator is running , then it is the location of the feed valve .

    If it releases with none of the above and more of hit of miss, look to the domestic . Indirect, coil or someone plumb in by mistake.....

    Is the relief under sized ? The btu rating of the valve should be higher then the btu rating of the boiler ...
  • Brad White
    Brad White Member Posts: 2,398
    Height and Pressure

    If you have a 3-story building, say 12 feet per floor and the fill point is five feet above the basement floor (just a guess here, do you even have a basement?) and the top floor radiator is within five feet of the third floor slab:

    Total system height in this example is 36 feet. Divide that by 2.31 you are correct gets you to 15.58 call it 15.6 PSIG. However it is good practice to add four or five PSI so you have at least that much at the top of the system.

    If your expansion tank is on the discharge of the circulator, all bets are off! Listen to Big Ed and Steamhead.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • tim smith
    tim smith Member Posts: 2,752
    Regarding water at top radiators

    Water at bleeder at top floor radiators is a good indicator as long as it is not an overhead feed system. Then you better count on another 6psi or so to get to attic. You probably want around 18 to 20 psi cold to be adequate. Tim
  • Jake_4
    Jake_4 Member Posts: 3

    Yes its pumping away. The bladder is on the suction side of the pumps. If I take the 15psi and add 5 extra psi for good measure, wont my heated pressure exceed my 30 psi relief valve?
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