So imagine that this steel container is instead the water line that enters your home (Unless you collect rainwater or make water from hydrogen and oxygen, you probably have one.) If it gets too cold, the water can freeze and can literally break your pipe. That’s bad. Now for some questions and answers.
Why doesn’t this happen more often in the south?
Residential water lines are almost always underground – and that’s a good thing. Although the air temperature can vary drastically from summer to winter, the soil temperature is much more constant. In southern states, this soil temperature is not very likely to drop under frost – so the water in the pipes will also be above freezing (and will remain liquid).
But there are a few exceptions. In some warm climates, not all parts of a water pipe system will be underground and pass through regions of air. (Heck, I have water pipes in the attic and I live in a warmer location). Although there is a small temperature difference between cold water (say 1 degree Celsius) and hot ice (0 C), there is a huge difference in energy. It takes a little energy to change water from its solid phase into a liquid. We call this the latent heat of fusion. For water, it has a value of 344 joules per gram. It might be hard to understand, so how about an example?
Suppose you have a liter of ice (with a mass of about 1,000 grams). If you want to take this ice at 0 C and turn it into water at 1 C, you would need 344,000 joules of energy (plus a little energy to raise the water temperature). How much energy is that? Well, suppose you have a smartphone with a 3,000 mAh battery (milliamp-hours). This is equivalent to 41,000 joules. So you might have enough energy to run your phone for a whole day, but you would need eight or nine of these phones to melt all the ice.
It’s actually a good thing. It means you can use melting ice to cool your drinks – and you don’t really need that much ice. This also means that you need to remove enough heat from the pipes to freeze them. A cold night will probably not be enough to make you break your pipes.
Does it help you let a faucet run?
Yes. OK, imagine you’re in a water pipe. (Yes, you are very small now.) If the water is stationary, you may be stuck in a part of the pipe that is exposed to cold air. In fact, you could freeze and then you should break the pipe. But now suppose it’s running water, caused by a faucet dripping lightly. You’re still a tiny person inside a pipe, but now you’re moving too. Go through the cold pipe section and it gets cold – but it doesn’t freeze. Instead, just move on to other parts of the house.
Oh, but more water from the main underground line enters that cold part of the pipeline. Would it freeze? It’s not as likely. Remember, the water pipe is at ground temperature, which is almost certainly not under frost. So the inlet water is not super cold and hopefully will not freeze.
What about isolation?
Isolation helps. If you wrap foam insulation around any exposed pipe, it does the same with your cooling or insulated cup. Insulation decreases the speed at which energy is transferred from hot work to cold work through a thermal interaction. If you put a cold drink on a table, the energy is transferred to the drink to cause the temperature to rise. Putting the drink in a cooler, on the other hand, increases the insulation and decreases the energy transfer rate, so as to heat the drink.