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Thread: Pipe Volume

  1. #1

    Default Pipe Volume

    Can anyone tell me how to work out how much water a lengh of pipe will hold. What I want to know is, how much water will it take to fill 500' of PEX pipe.
    Regards
    tel

  2. #2
    Rancher
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    Since you didn't give me the diameter of the pex pipe, you'll have to make the calculations yourself.

    Pi x R squared x lenght (500' or 6,000")

    Pi = 3.1415
    R = Radius of the pipe, i.e. half the diameter.

    So for 3/4" pex

    3.1415 x (.375 x .375) x 6,000 = 2650 cubic inches

    2650 / 144 = 18.4 cubic feet

    18.4 X 7.48 = about 138 gallons (7.48 gal per cubic foot)

    Rancher
    Last edited by jimbo; 10-18-2009 at 12:03 PM. Reason: correct the equation for total gallons. ( X instead of /)

  3. #3
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Don't forget to subtract the pipe's wall thickness when you compute the radius. PEX complies with SDR 9, so the wall thickness is 1/9 of the diameter. For 3/4" pipe, that's .083", so making this adjustment throughout, and using 1728 cu in per cu ft (thanks, jimmym) I get about 7 gallons.
    Last edited by Mikey; 09-07-2006 at 10:20 AM.

  4. #4

    Default Pipe volume

    Sorry about that.. 1/2 pex, I want to use it for underfloor hotwater heating system.
    Thanks
    tel

  5. #5
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    OK. For 1/2" PEX, about 3 gallons per 500 feet.
    Last edited by Mikey; 09-07-2006 at 10:19 AM.

  6. #6
    DIY Member jimmym's Avatar
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    Quote Originally Posted by Rancher

    2650 / 144 = 18.4 cubic feet

    Rancher
    That's 1728 in^3 / 1 ft^3. Not 144.

  7. #7
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Default I need to go back to 3rd grade.

    Correcting for lots of screwups, the real numbers are as edited (or as will be edited shortly) above. I think.
    Last edited by Mikey; 09-07-2006 at 10:20 AM.

  8. #8

    Default Pipe volume

    Thanks guys..
    That was about what I thought.. My problem is I am thinking of having underfloor hotwater heating system installed in my family room, and the contractor is telling me I need about a 30 gal elec hotwater tank, seems alot to me.. Any thoughts?
    Cheers
    tel

  9. #9
    Rancher
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    Opps, not enuf coffee

  10. #10
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    The problem is you're not just heating the 3, 7, 10, or however many gallons it might be. You're maintaining a flow at a desired temperature. Depending on the flow rate and temperature differential, you need a certain number of BTUs, which translates into a certain number of kVA, kwH, etc., which determines the size of the WH. There are a couple of guys here who can do these calculations off the top of their head, but they'll need more data than we have so far. The odds are your contractor has already done these calculations (ask him to explain) and determined the 30gal WH is appropriate.

  11. #11
    In the Trades Bob NH's Avatar
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    Before you look at gallons, you need to consider BTUs per hour.

    How many BTUs per hour do you need?

    Then you need a heater that will deliver that many BTUs per hour.

    1 kW = 3413 BTU per our if you are heating with electricity.

    If you are looking at a gas heater, then you need to look at the rating of the heater, usually in Net BTU/hour.

  12. #12

    Default Pipe volume

    Thanks to every one that has replied to my question. it has been a great help.
    regards
    tel

  13. #13
    Moderator & Master Plumber hj's Avatar
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    Default heater

    6 gallon, 30 gallon, or more is basically immaterial. You have to size it for the recovery, not the storage, so the energy input is what counts, not the size.

  14. #14
    DIY Junior Member BubbaBob's Avatar
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    Default Make it simple and economical

    I've just built a 706 sq ft yurt (google them...they are interesting) and for heat I installed radiant floor heating using a Takagi TK-Jr propane tankless heater. My floor has 700 linear feet of 1/2 pex-a in 4 zones, and the expansion tank is a 2.2 gal Watts, which is more than enough.

    Inexpensive, economical operation, efficient, trouble free. What more could one ask for?

  15. #15
    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Quote Originally Posted by BubbaBob View Post
    I've just built a 706 sq ft yurt (google them...they are interesting)
    Neat. I guess you don't live in the suburbs. What's it for?

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