Why Does a Dripping Faucet Prevent Frozen Pipes?

Short answerUtah State University Extension says leaving a faucet running works to keep a line from freezing, though it wastes water. University of Illinois suggests a trickle of hot and cold at night from a faucet on an outside wall. The sources don't explain why. Our own reasoning is that moving water is harder to freeze.

What this costs

Our national estimates, not quotes.
Option	Job	Low	High
Repair	Pipe Repair	$130	$800

How to use it

Use a faucet on an outside wall. University of Illinois says hot and cold. Utah State notes hot lines freeze too.
Keep it to a slow drip or trickle. NC State Extension suggests constant dripping for pipes that may be on an exterior wall.
Do it during freezing nights. Utah State says it wastes water, so it's for when permanent fixes aren't possible.

Why it matters

Utah State says that as ice expands, it can crack or split a pipe. University of Illinois says an eighth-inch crack can release up to 250 gallons a day. We'd call a drip a small cost compared with a burst pipe.

What works better over time

University of Illinois says to locate and insulate the pipes most at risk. It also says to keep heat no lower than 55 degrees. Know where your main water shutoff is, so you can act fast if a pipe does split.

What isn't settled

We didn't find an official figure for how fast to drip or how cold it needs to be before you bother. Follow your local water utility if it issues advice during a cold snap.

Frozen Pipes? How to Thaw Them Safely

Common questions

Does the faucet need to drip hot or cold?

University of Illinois says hot and cold. Utah State notes hot water lines can freeze too, and people rarely leave those running.

Will dripping waste a lot of water?

Utah State says it does waste water and suggests it only when more permanent methods aren't possible. We'd save it for the coldest nights rather than the whole winter.