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  1. #1
    Join Date
    Oct 2009
    Location
    Lake Zurich, IL
    Posts
    60

    Your guess? How fast water pipes freeze when assuming....

    What's your guess? How fast do water pipes freeze AFTER indoor temperature hits 32*F on it's way to 25*F?

    Let's assume also:
    - water pipes are all in interior walls
    - water is not moving (stagnant)


    I know building heat loss varies dramatically... that's why I'm saying to assume when indoor temp falls to 32*F.

    I'm trying to assess my risk exposure to frozen water pipes when the electricity goes out. Since we are on a well, a backup generator would be a nice convenience, but I'm trying to separately assess risk of frozen water pipes.

    Thanks for your guesses,
    Jim

  2. #2
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Might want to consider shutting the breaker off to you're well pump and Hot Water Heater, drain to the lowest point possible, environmentally friendly antifreeze in toilets, etc. Then go find somewhere warm until the power comes back on.

    "Or" get an electrician to properly connect a generator.

    How long, etc, all depends on X,Y and Z....... who knows

  3. #3
    Join Date
    Feb 2004
    Location
    Pacific NW
    Posts
    565
    No guess, calculation.

    Say you have 3/4" Cu pipe.
    3/4" pipe holds approx 5-1/2 cu in of water (0.2#), and it takes 143 BTU per pound of water to freeze. Pipe needs to lose about 30 BTUs per foot to freeze.


    So, let us guess the pipe is bare, no insulation on it. You have a temp difference of 32-25 = 7F

    3/4 Cu pipe has 32 in sq per foot of surface area.

    a typical number used for air on outside to liquid on inside pipe heat transfer factor is 4 BTU/hr-degF /sq ft for a horizontal pipe in still air, and can range from 1 to 10 depending on drafts or restriction of convection air. We will just use the number 4.

    That gives 30/4 = 7.5 hr-deg F, you have 7 deg F differential, so your pipes will freeze in just about 1 hour if you had a square foot, but you only have 32/144 sq ft area on the pipe. So, say 4 hrs to freeze. 'Could' freeze in as quick as 1 hour if the pipes are in a wind or very drafty wall.

    Hope this does not smack of diy, but you can run a test at home easy enough. Fill a sealed piece of pipe with water, attach your type K thermocouple, hook up to your data logger, stick in your freezer at a known temperature.
    After the pipe bursts, look at how long it takes between the time T=32 till when it reaches 31.9F. Ratio that time by the temp differential in the freezer vs 7F.

    BTW, for 0F outside, it takes most of the night to freeze a 24 oz can of steel reserve <G>
    Last edited by junkhound; 02-11-2011 at 01:51 PM. Reason: add info

  4. #4
    Join Date
    Dec 2006
    Location
    Litchfield,Il
    Posts
    565
    I am going to guess . lol 25*deg amb. db and indoor db temp of 32*deg.

    copper lines - 3 days
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  5. #5
    Join Date
    Feb 2009
    Location
    Fox Lake IL
    Posts
    438
    house is at 70 power goes out could take 8 hours to go down to 55 and 16 hours to go down to 32 now it need to get colder to freeze the pipes to break the copper line. I would say 48 hours. you can turn your furnace off and see how long it takes.in the last few days with the temps down to -20 at night could only take 12 hours. as this week end it will be 34 outside could take days.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,722
    Pressurized well water in a copper or steel/galvanized pipe probably won't freeze at 32F outdoor temp. Too many minerals in it.
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  7. #7
    Join Date
    Feb 2010
    Location
    butler pa
    Posts
    1,073
    had 2 above ground cabins at a local church retreat camp froze up after
    furnaces failed under 48 hrs..cracked commodes=shower heads..and what else
    to be found by maint guy..first time id seen 28 degrees displayed on a digital tstat

  8. #8

    Handy Calculator

    Here is a link to a calculator that will give you a decent calculation.

    http://www.wbdg.org/design/midg_design_tffc.php

    You will notice that it doesn't take into account latent heat however and also makes a few other assumptions. So the value calculated can be used as a minimum time to freezing. Actual time will be longer.

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