Does a dripping faucet keep the pipes from freezing?

Cecil's Columns/Staff Reports
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After providing an excellent answer to this question at http://www.straightdope.com/mailbag/mpipefreeze.html ,the following statement was made:

Although true, isn’t this pretty much a moot point in northern climes where the commonly used (albeit more expensive) spigots actually cut off the water about a foot inside the wall as opposed to those spigots commonly used south of the Mason-Dixon line which turn off the water right at the spigot (e.g., out in the exposed air), thereby welcoming the freezing to occur?

I never remember wrapping socks around my spigots when I lived on the northern side of the continent.

Then again, perhaps in extremely northern climates, even the internal cut off is insufficient.

Edited to fix link – CK Dex

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What I’ve always heard is that the dripping isn’t really to keep the pipe from FREEZING, but to keep it from BURSTING.

Y’see, what they’ve found is that, when a pipe bursts, it isn’t DIRECTLY from the expanding ice pushing outward on the walls of the pipe. The ice, as noted, forms from the outside and moves inward. However, once a block has formed, it will expand outwards as more ice forms. On the water-company side there’s no problem, but there is an amount of water trapped between the ice and the faucet.

As the water freezes, it expands, raising the water pressure higher and higher. Eventually there is enough hydraulic pressure to burst a weak point, such as a nearby joint. If you let the faucet run a little, even a drip, the pressure will be relieved and won’t have near as much chance of giving you a nasty leak.

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The above link is broken - it contains the comma following the “.html”. Here is a fixed link:
http://www.straightdope.com/mailbag/mpipefreeze.html

I’m in Chicago, and I grew up in Iowa (which gets just as cold). It’s not the outside spigot that is being talked about. It’s inside.

The problem is that indoor pipes often run through insufficiently-heated areas. Some builders of attached-garage homes run pipes through the garage. Or just pipes in an outside wall that isn’t insulated well enough. On very cold days (especially with wind), the inside of the wall can get below freezing.

There’s one part of the equation that SDSTAFF Ken didn’t mention. Depending on how far North you live, there is a depth in the ground that is (I think) called the frost line. It is the deepest point that the ground freezes hard during winter. Underground water pipes are buried well-below the frost line, meaning that the dirt surrounding those pipes never gets below freezing. (That is also why deep caves stay a fairly constant temp during both summer and winter.)

Thus, if you keep your water dribbling, you are constantly bringing fresh above-freezing under-ground water into a pipe that is exposed to below-freezing air. But, depending on the length of pipe, and how cold the unheated area is, it is a race against time. The warmer water in the pipe cools as it flows. If it is flowing too slowly, it will reach freezing temperature before it has reached the end of the unheated run of pipe. So, the colder the weather, the faster you have to let the water run to prevent freezing.

Just insulating the pipes better just gives you more time. Maybe you only use a particular sink for brushing your teeth in the morning. If the pipe is well-enough insulated, it can slow down the cooling process to the point that it only needs a once-a-day hit of fresh water. (Just be sure to run the water long enough to completely replace the water in the pipe … a good idea even in the summer to minimize impurities.)

But if the ambient temperature around the pipe stays below freezing, it doesn’t matter how well you insulate the pipe, it will eventually freeze if no fresh water is allowed to enter. (E.g. if you are on vacation in the Bahamas during a week of sub-zero temps at home.)

Here’s a silly invention idea. Have a device that measures the temperature of the water coming out. As the water temp approaches 32 degrees, the device increases the water flow. As the water temp rises, decrease the flow. This would let you minimize the impact on your water bill.

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Ken also said,

"First, the obvious: water does not freeze in an instant (except in cartoons). "

Well, that is except in cartoons and P-chem labs. You can supercool water well below the freezing point. Apply a little mechanical energy (flick its container with your finger), and it’ll freeze in less than a second. This phenomenon was actually a big problem determining the freezing point of ultrapure water. It doesn’t like to change states without a little prodding.

(BTW: This is probably the only time PbZep and Supercool will appear in the same post).

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And then there’s Vonnegut’s “ice 9”. :wink:

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sford is mostly correct. As a resident of the aforementioned Arctic, I have a few bits to add.

While you mentioned the frost line, that is primarily an issue south of 60. We have a bigger problem with permafrost. That can be quantified as the maximum depth the ground thaws in the summer. :slight_smile:

We use a combination of methods to keep the pipes from freezing and bursting. The mains are just well-insulated, and since the water moves constantly, it is not at much risk of freezing. Monitoring the water flow also tells you when an ice buildup is happening, although, sadly, this sometimes fails too. I’ve seen the results of two frozen mains over the past ten years or so. Fortunately, since they affected nobody I knew, I had the leisure to be amused.

We also use heat tape on water pipes, although this practice has fallen into disfavour lately. Something about heat tape being the cause of several fires…

Bleeder valves used to be very popular. This is a small spigot, frequently located in laundry rooms, that you turned on once it turned ten or twenty below, and left on until it was above ten degrees for at least two weeks. However, this has begun to be less popular (in fact, I vaguely recall some sort of bylaw saying you can’t put them in anymore), and since it looks like we’ll actually have to PAY for our drinking water sometime in the next ten years, it’s probably a good thing.

And alas, the invention sford mentions has already been done. I have one I am testing for the City of Whitehorse in my house. It’s a little grey box that connects to my old bleeder valve, and does pretty much what you say. It goes one further, and releases only set amounts of water for a specified time. However, I still find it goes on at all kindsa weird times, even when it’s not all that cold. I guess that’s why they call it a test, eh?

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HA! It might be that the device doesn’t know what the outside temp is, so it has to periodically turn on the water to see what the pipe temp is.