How cold does it have to be for pipes to freeze?

Which pipes freeze first around here?

In the order we actually find them: hose bibs with a hose still attached, supply lines running through rim joists, lines in exterior walls — especially kitchen sinks on an outside wall — unheated crawl spaces, and lines running through an attached garage.

Buried water service is rarely the culprit. Minnesota code requires that line at least 12 inches below finish grade and at least 12 inches below maximum local frost depth, and it usually holds.

What is the January pattern?

Almost every bad freeze week here follows the same script. A stretch of mild weather melts the snow cover. Then the wind swings around and the temperature drops for four or five days straight. No snow on the ground means no insulation, and wind means the cold gets driven into every gap in the sheathing.

The bursts usually happen a day or two after the coldest night, when things thaw and the split lets go. That is why the phone rings hardest on the warm-up.

What can you do during a cold snap?

Open the cabinet doors under sinks on exterior walls so house heat reaches the pipes. Let a pencil-thin trickle run from the fixture farthest from the water heater. Keep the thermostat at a normal setting even if you are away — setting it to 55°F to save money is exactly how an unheated-house freeze claim starts.

Disconnect any hose that is still on a spigot. That single step prevents more split hose bibs than everything else combined.

What if a pipe is already frozen but has not burst?

Open the faucet it feeds so melting water has somewhere to go. Apply gentle heat — a hair dryer or a space heater at a distance — working from the faucet back toward the frozen section. Never use an open flame. If you cannot find it, or if the line is behind a finished wall, call.

Related questions

At what temperature do pipes burst?

Pipes burst from the pressure ice creates, not directly from temperature. Freezing generally begins for exposed household pipes around 20°F outside, and the split often shows up when the line thaws.

Should I leave faucets dripping in Minnesota?

During a sustained cold snap, a slow trickle at the fixture farthest from the water heater is cheap insurance for the lines most at risk.

How long does it take for a pipe to freeze?

An exposed pipe in an unheated space can freeze in a matter of hours in a hard cold snap with wind. A pipe in a heated wall cavity may take days, or never.