plumbing in a cold zone

Discussion in 'Remodel Forum & Blog' started by geofixit, Aug 29, 2008.

  1. geofixit

    geofixit New Member

    Messages:
    3
    I want to run a pex line through my ceiling for a ceiling mounted shower head. On the other side of the ceiling is the attic (cold zone) wich has two layers of pink ceiling insulation. if I keep the pex well insulated and close the the drywall do you think there will be a freezing issue?
  2. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    Redwood flips the coin and darn it lands on the edge!:eek:
    Where are you located?
  3. geofixit

    geofixit New Member

    Messages:
    3
    South side of Georgian bay, Ontario, Canada
  4. geofixit

    geofixit New Member

    Messages:
    3
    Can be cold winters.
  5. leejosepho

    leejosepho DIY scratch-pad engineer

    Not unless you already occasionally experience frost on the ceiling.
  6. krow

    krow Plumber

    Messages:
    906
    Location:
    Ontario, Canada
    In Georgian bay?

    Yes there will be a freezing issue. Any time a water pipe runs through an exterior wall and or, in your case, attic space
    , there will always be a chance of it freezing. No matter how well you insulate, there is alaways a chance of freezing
  7. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    Heck I see pipes in attics freeze down here...
    We're nowhere close to being up in that frozen wasteland!:eek:
  8. D.Smith

    D.Smith New Member

    Messages:
    63
    Location:
    Georgia
    I am no expert if all he is running is a shower head I would imagine that the pipe would drain out after each shower leaving nothing to freeze? Although if there is any water that freezes would take showers a difficult issue.
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,689
    Location:
    Cave Creek, Arizona
    water

    A shower line SELDOM drains out because of the logistics of getting air into the pipe while draining the water out. IF there were side wall heads running at the same time THEN the overhead water would drain down out of them, but otherwise the water will stay in the pipe, get colder and colder regardless of how much insulation, (unless heat from the building could surround the pipe), and then freeze and split.
  10. that's more insurance!

    Assuming the shower water pipe came UP under the side wall shower heads, water would dribble out through one or both shower heads. But, if the pipe came across the attic over to the shower, then putting a side wall shower head under the ceiling mounted one would not give much insurance of draining the pipe run crossing the attic.

    Geofixit, you better have some serious eyeballs look at your space.

    Ultimately nothing guarantees there will be no freezing. Not even a lot of insulation, in a large airtight (closed-to-air) enclosure. Insulation slows down the transfer of heat and cold. It does not "keep things warm".

    The longer you go without running water in the shower pipe, the colder the stagnant pipe water gets, second by second. Then, at some temperature point, things stabilize assuming the indoor and outdoor temperatures are stable in this example.

    When the heat transfer from the heated part of the house into your shower pipe equals the heat transfer from the shower pipe out to the great outdoors, the water in the pipe has reached its stable temperature. Whether the temperature in the pipe reaches a steady-state temperature above or below freezing is not knowable in advance. Too many variables. How well you execute your insulating and sealing is a major factor.

    The colder the outdoor temperature, the greater the heat loss. Duh. When the temperature spread (between room temp and outdoor temp) doubles, heat loss is quadruple as fast. Ah ha.


    David
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,059
    Location:
    New England
    This might be an ideal installation for a toe tester; basically, use a tub spout with a divertor on it to check the shower temperature mounted low, then pull the divertor to shower. Then, instead of the line staying nearly full when you shut off the water, it would drain back down through the pipe to the spout.
  12. that would work best


    that is probably the only way to be sure you wont have water standing in the outside pipe all winter long...

    just tell your wife that the spout is for washing. your feet...

  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,689
    Location:
    Cave Creek, Arizona
    toe tester

    The toe tester would only be a solution if the overhead shower was the only shower head. Using a diverter to add a conventional head or side sprays would defeat its purpose.
  14. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    I think the key here is the Ratio of the R values vs the Ratios of the temperatures.

    1. Lets assume that the pex remains in contact with the Sheetrock with a air gap with about a R4.
    2. Lets assume a R36 above that and you have enough cellulose insulation to prevent "piping"
    3. Lets assume a room temp of 70F and a outdoor temp of -40F

    That would leave the Pex at
    Temp = 70F - ( (70F- -40F) * (R4/R36) ) = 57F

    So the PEX line would be safe as long as you lay something over it to keep it against the Sheetrock and to prevent insulation from getting under it.

    I would also suggest blowing a light layer of cellulose insulation over the fiberglass bat to prevent air "piping" and thus get the full R value.
  15. PEW

    PEW DIY Senior Member

    Messages:
    487
    I am in Delaware with all plumbing in the attic. Not as cold as where you are but, if you are talking of keeping the pipes above a heated space, and the pipes are kept under the existing insulation, and the pipes are not insulated, there should be no problems.

    Keep the pipes near the top of the insulation, that is another story.

    [​IMG]
    Last edited by a moderator: Dec 22, 2008
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