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    rrekih's Avatar
    rrekih Posts: 19, Reputation: 1
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    #1

    Dec 20, 2009, 01:23 PM
    Calculate head
    How do I calculate the head pressure in a 1/2" pex radiant system.
    Did some looking on the web, but couldn't find anything conclusvive.
    I would suspect that the pex would have so much head per ft. and then have to add connections etc.
    jlisenbe's Avatar
    jlisenbe Posts: 5,020, Reputation: 157
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    #2

    Dec 20, 2009, 01:32 PM

    The commonly used figure is about 0.4 pounds of pressure per foot of rise. Speedball knows the exact figure. I'm not sure what a "radiant system" is, so I might be off on my answer relative to what you are wanting to know.
    speedball1's Avatar
    speedball1 Posts: 29,301, Reputation: 1939
    Eternal Plumber
    		  
    #3

    Dec 20, 2009, 01:47 PM

    Jlisenbe nailed it!
    The coirrect way to calculate the head pressure of ANY column of water whether it's in a Pex system or a water tower is to multiply the height times 0.434
    Hope this answers your question. Yom
    rrekih's Avatar
    rrekih Posts: 19, Reputation: 1
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    #4

    Dec 20, 2009, 02:44 PM

    That would get you the height calc. but what about the friction of the pipe and connections?
    Does this also contribute to the head?
    speedball1's Avatar
    speedball1 Posts: 29,301, Reputation: 1939
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    #5

    Dec 20, 2009, 03:45 PM

    that would get you the height calc
    No! That would give you the PSI at the base of the column. Just what are you attempting to figure that you want to factor in line loss. Before we take this any farther let's have more details. Why the question? Tom
    jlisenbe's Avatar
    jlisenbe Posts: 5,020, Reputation: 157
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    #6

    Dec 20, 2009, 03:47 PM

    I looked up pressure loss for pvc one time. The bottom line is, it varies depending upon pipe size, the length of the run, and the volume being pushed through the pipe. For short runs such as I suspect you are talking about (tens of feet), it was, as I recall, insignificant.

    You might find this site helpful.

    Hazen-Williams Equation - calculating Friction Head Loss in Water Pipes

    OR this one

    http://www.pondarama.com/html/friction_loss_charts.html
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