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Does anyone have a good answer how comes that the water in the pipes in our houses doesn't freeze even if it is -40 celsius for a whole week? of course assuming we don't make the water to fluid in it

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up vote 4 down vote accepted

To the points akhmeteli already mentioned there I want to add two reasons:

  • In larger buildings there will always be someone using water, so the water coming from the ground at approximately 6°C will keep the pipes warm enough
  • A brick wall with a thickness of a few centimeter provides already good isolation, so a little bit of heating at the inside will keep the temperature well above the freezing point

Especially the isolation is also true for pipes outside in the ground, the thermal conductivity of soil is so low that in a depth of 2 meters it will stay warm for the whole winter. This does not work in very cold climates though, when it will be below zero all year long. This permafrost can reach down hundreds of meters.

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There is no such thing as miracles. If water in the pipes does not freeze at -40 degrees Celcius, there is a reason for that. Either the pipes are indoors in heated spaces, or they are heat traced, or they are drained, or they are insulated, or they are buried, or water in the pipes is running (or at least dripping), at least intermittently. I remember such cold (-40 degrees C) in Moscow many years ago. In our 14-storey house, the elevator landings were heated by large, very heavy cast iron radiators. At almost all landings, water in the radiators froze, and radiators burst.

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