Pipe Volume

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by tel, Sep 7, 2006.

  1. tel

    tel New Member

    Messages:
    6
    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. Rancher

    Rancher Guest

    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 a moderator: Oct 18, 2009
  3. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,714
    Location:
    Central Florida
    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: Sep 7, 2006
  4. tel

    tel New Member

    Messages:
    6
    Sorry about that.. 1/2 pex, I want to use it for underfloor hotwater heating system.
    Thanks
    tel
  5. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,714
    Location:
    Central Florida
    OK. For 1/2" PEX, about 3 gallons per 500 feet.
    Last edited: Sep 7, 2006
  6. jimmym

    jimmym New Member

    Messages:
    69
    Location:
    New York
    That's 1728 in^3 / 1 ft^3. Not 144.
  7. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,714
    Location:
    Central Florida
    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: Sep 7, 2006
  8. tel

    tel New Member

    Messages:
    6
    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. Rancher

    Rancher Guest

    Opps, not enuf coffee
  10. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,714
    Location:
    Central Florida
    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. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    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. tel

    tel New Member

    Messages:
    6
    Thanks to every one that has replied to my question. it has been a great help.
    regards
    tel
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,680
    Location:
    Cave Creek, Arizona
    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. BubbaBob

    BubbaBob New Member

    Messages:
    1
    Location:
    N GA mountains
    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. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Neat. I guess you don't live in the suburbs. :) What's it for?
  16. Gary Slusser

    Gary Slusser That's all folks!

    We already have 6 solar panels and 6 6volt AGM batteries BUT I'll ask for 2-3 more solar panels, 2-4 more AGM 6 volt batteries and a central vac system for my totally off grid motor home. Then I wouldn't have to run the generator at all. A yurt is immovable LIKE A HOUSE!
  17. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,680
    Location:
    Cave Creek, Arizona
    volume

    And to mess up the original calculations, PEX i.d. is NOT 3/4". It is between 9/16 and 5/8 meaning that its volume is about 75% of copper tubing.
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