Can pipes freeze in Phoenix?

Water freezes at 32 degrees Fahrenheit, but the pipe around it does not fail right away. The pipe has to lose enough heat for the water inside to turn to ice, and that takes time and deeper cold. The U.S. Department of Energy puts a useful marker on it. The DOE says that in southern states, where homes are built for warm weather, pipes generally start having problems when the temperature drops to about 20 degrees Fahrenheit.

The DOE puts the warning plainly: "In southern states where pipes are more likely to be exposed to cold, the temperature alert threshold is about 20 degrees Fahrenheit." That 20F figure matters for Phoenix because our buildings match the southern-state pattern. Pipes often run through unheated garages, along outside walls, and across vented attics with little or no insulation. There is no buried frost line to protect them and no habit of leaving heat on for the plumbing.

Speed is the other half of the risk. The American Red Cross notes that when the temperature outside falls below 20F, pipes can freeze in as little as 6 hours. A single overnight low in the teens, which Phoenix does see during a strong cold front, is enough time for water in an exposed line to freeze solid. You do not need a week of cold. You need one bad night.

When water freezes, it expands. That expansion builds pressure inside a closed section of pipe, and the pipe or a fitting eventually gives way. The break often shows up later, when the ice thaws and water rushes out of the crack.

Not every pipe in your home faces the same danger. The ones that freeze are the ones with the least protection from the cold. In a typical Phoenix house, the at-risk pipes are predictable.

• Uninsulated exterior pipes. Any supply line running along an outside wall or across an open patio loses heat fast once the air drops into the 20s.
• Hose bibs, especially on north walls. Outdoor faucets sit fully exposed, and north-facing walls get the least winter sun, so they stay coldest the longest.
• Garage supply lines. Garages are rarely heated, and pipes feeding a water heater or laundry hookup in the garage can drop to outdoor temperatures.
• Attic runs. Many Phoenix homes route water lines through a vented attic. Cold air pours in, and those pipes can be colder than the rooms below them.
• Pool equipment. Pumps, filters, and the exposed plumbing around pool gear sit outside with no shelter and freeze readily on a hard night.

The common thread is exposure. A pipe inside a heated, insulated wall almost never freezes here. A pipe sitting in cold, moving air with no covering is the one that fails. The National Weather Service Phoenix office issues freeze warnings ahead of these cold snaps, and those alerts are your cue to check the spots above.

The good news is that protection is cheap and most of it is one-time work. A few hours before a cold front arrives, you can cut your risk sharply. Here is what works, roughly in order of payoff.

• Insulate exposed pipes. Slide foam pipe sleeves over any exterior, garage, or attic lines you can reach. For pipes that stay very cold, UL-listed heat tape adds a controlled heat source. Use a product rated for the pipe material and follow the maker's directions.
• Disconnect and drain garden hoses. A hose left attached traps water in the hose bib and the line behind it. Pull every hose, drain it, and store it.
• Add insulated hose-bib covers. These foam or hard-shell caps snap over an outdoor faucet and trap the small amount of heat coming through the wall. They cost a few dollars each.
• Let a faucet drip during a hard freeze. Open a faucet fed by a vulnerable pipe to a slow drip. Moving water resists freezing, and an open faucet relieves the pressure that actually splits a pipe.
• Open cabinet doors. Under sinks on outside walls, open the cabinet so household heat can reach the pipes.
• Keep heat at 55F or higher if you travel. If you leave during winter, do not shut the heat off. Set the thermostat to at least 55F so indoor lines stay warm.

These steps cost little next to the price of a burst pipe and the water damage that follows. The insulation and covers stay useful winter after winter, so the work pays off more than once. A pipe that is wrapped, covered, and dripping during a cold snap is one you rarely have to think about again.

If you turn on a faucet during a freeze and only a trickle comes out, you likely have a frozen pipe that has not yet broken. Keep that faucet open. As the ice melts, the running water helps clear the blockage and gives the pressure somewhere to go. You can warm the frozen section with a hair dryer or a space heater kept at a safe distance. Never use an open flame, and never use a torch on a pipe.

If a pipe has already burst, the priority is to stop the water. Shut off the water at the fixture's local valve if it has one, or at your home's main shutoff. Knowing where that main valve is, and being able to turn it before a leak starts, is the single best thing you can do to limit damage. For how to find and operate your home's main valve, see our guide on the main water shutoff. After the water is off, open faucets to drain the lines and reduce pressure.

A leak from an outdoor faucet is a common winter problem, since hose bibs freeze first and a frost-split stem may not show until spring. If your outdoor faucet drips or leaks after a cold spell, our page on an outdoor faucet or hose bib leaking covers the likely causes and fixes.

Pipe material affects how a freeze plays out. The Plastics Pipe Institute notes that flexible piping can expand somewhat under freezing stress, while rigid copper tends to split. Either way, a frozen line that has thawed should be checked for leaks before you trust it again. A small crack can weep slowly for days before it floods a wall or ceiling. Pool plumbing deserves the same look after a freeze, since pumps and filters hold standing water that can crack a housing without any obvious leak above ground.

It also helps to know your home before the cold arrives. Walk the garage, the attic access, and the outside walls once in early winter and note which pipes are bare. Those are the lines to wrap and watch. A short list taped inside a cabinet door means you are not hunting for vulnerable spots in the dark when a freeze warning lands at 9 p.m.

A frozen pipe is rare in Phoenix, but it is real, and the homes here are the kind the DOE flags as least ready for it. A little foam, a hose-bib cover, and a dripping faucet on the coldest nights will carry most homes through a desert cold snap without a single break.