SAWS News: Jack Frost Nips at Water Pipes at 20 Degrees and Below
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Edwards Aquifer

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Jack Frost Nips at Water Pipes at 20 Degrees and Below

Source: Institute for Business & Home Safety

Homeowners in our area need to be alert to the danger of freezing and bursting water pipes when the outdoor temperature threatens to drop to 20 degrees F.

That's the temperature at which ice is likely to start forming in water pipes located in an unheated portion of a house.

Once ice forms into a blockage in a pipe, continued growth of ice in the pipe can lead to excessive water pressure. It's pressure of the water that has no place to go when ice builds that causes the pipe to burst, rather than ice pushing against the wall of a pipe.

Although 20 degrees F is well below the freezing temperature of water, two factors make this the critical outdoor temperature:

  1. The temperature of an unheated portion of a house is almost always at least a few degrees above the outdoor temperature. For example, an insulated attic may be at 37 or 38 F when the outdoor temperature is 32 degrees F.
  2. Water "super cools" several degrees below freezing before any ice begins to form.

In research tests at the University of Illinois, water pipes placed in an unheated, insulated attic consistently started forming ice when the outdoor temperature dipped just below 20 F.

The 20 degree F threshold is primarily for homes in the south and other areas where freezing may occur only once or twice a season.

Homebuilders in these areas often overlook the threat of freezing and place pipes in vulnerable locations.

Builders in the north, where temperatures in the teens and lower are common, routinely install more building insulation and usually do not place pipes in unheated portions of a building.

There are several precautions homeowners can take when the temperature is expected to dip into the low 20s:

  • Seal all openings where cold air can get at unprotected water pipes. It's especially important to keep cold wind away from pipes, which speeds up the freezing process.
  • Cover pipes with foam or fiberglass insulation sleeves, the thicker the better.
  • Install heating tapes or cables on vulnerable pipes. Be sure to follow manufacturer instructions carefully to avoid starting a fire.
  • Leave cabinet doors open under the kitchen and bathroom sinks to allow warmer room air to circulate around pipes.
  • Let faucets drip slowly to keep water flowing through pipes that are vulnerable to freezing. Ice might still form in the pipes, but an open faucet allows water to escape before the pressure builds to where a pipe can burst. If the dripping stops, it may mean that ice is blocking the pipe; keep the faucet open, since the pipe still needs pressure relief. (Note: If you choose this option, SAWS will not be able to credit your account for the excess water use.)

Article © Institute for Business & Home Safety. Used with permission.

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