How do I thaw a frozen pipe safely?

The faucet tells you. The American Red Cross says: "If you turn on a faucet and only a trickle comes out, suspect a frozen pipe." Utica National's risk management guide describes the same sign more bluntly: an open faucet with no water coming out.

Next, figure out where the ice is. The Red Cross says likely places for frozen pipes include "against exterior walls or where your water service enters your home through the foundation." It also lists pipes most likely to freeze:

• Pipes exposed to severe cold, like outdoor hose bibs, swimming pool supply lines and sprinkler lines
• Supply pipes in unheated spaces such as attics, garages, crawl spaces and kitchen cabinets
• Pipes that run along exterior walls with little or no insulation

In a Phoenix home, that usually means the pipe coming out of the ground to the house, a hose bib, a line in the garage, or pipe in the attic. Utica adds that cracks and openings where cables or phone lines enter an outside wall let cold air flow across pipes and speed up freezing. If one faucet is dry and the others work, the frozen section is on the line feeding that faucet. If the whole house is dry, look near where the main line enters.

Work in this order:

1. 1Find your main water shutoff first. Know where it is and make sure you can turn it before you add any heat. Utica warns that "A rupture may be initially sealed by the ice blockage," and that flooding happens "when the ice blockage thaws out." You want to be able to stop the water in seconds.
2. 2Open the faucet. The Red Cross says to keep the faucet open, because as the frozen area melts, "water will begin to flow through the frozen area," and running water helps melt the rest of the ice.
3. 3Warm the pipe gently. Use one of the heat sources below on the frozen section, and never a flame.
4. 4Keep going until full pressure returns. The Red Cross says to "Apply heat until full water pressure is restored."
5. 5Check every other faucet. The Red Cross notes: "If one pipe freezes, others may freeze, too."

Opening the faucet isn't only about letting water out. Research from the University of Illinois Building Research Council found that pipes don't burst simply because ice pushes on the walls. Bursting happens when ice blocks the pipe and then "further ice growth applies dangerously high pressures to a confined water volume." Utica's guide explains the upshot: "A pipe that is open on one end cannot be pressurized and will not burst." An open tap gives that trapped water an exit while you work. Our page on whether cold temperatures alone burst pipes covers the science in more depth.

### Which heat sources are safe?

The Red Cross lists four ways to apply heat:

• An electric heating pad wrapped around the pipe
• An electric hair dryer
• A portable space heater, "kept away from flammable materials"
• Towels soaked in hot water wrapped around the pipe

Not every source agrees on the hair dryer. Utica National's guide says "Thawing a frozen pipe with an open flame or hair dryer should never be attempted." Hot towels and a heating pad avoid that disagreement. If you do use anything electric, keep it and its cord out of any water that drips or pools while the pipe thaws, and plug it into a dry outlet.

### What should you never use?

Anything with a flame. The Red Cross says: "Do not use a blowtorch, kerosene or propane heater, charcoal stove, or other open flame device." A torch can overheat the pipe or set the wall, insulation or framing behind it on fire. Combustion heaters and charcoal indoors add carbon monoxide to the danger. If a flame is the only way to reach the pipe, the pipe needs a plumber, not a torch.

Stop the water first. Utica's guide says: "If a pipe bursts, the main valve should be shut off and the faucets left open until repairs are complete." Leaving the faucets open drains the water still in the lines so less of it ends up in the wall.

Signs a pipe broke while it was frozen:

• Water spraying or dripping once the ice melts
• A wet spot on a ceiling or wall near the frozen section
• A pipe that looks bulged or split
• Water pressure that comes back weak at one faucet while others are fine

A split doesn't always show up right away. Utica notes that pipes typically burst "at locations where freezing last occurs," which is not always where the ice was. So after the water flows again, watch the pipe you thawed and the walls around it for the next day or two. Our guides on what to do first after a major water leak and how to shut off water to a single fixture cover the next steps.

The Red Cross draws the line clearly: "If you are unable to locate the frozen area, if the frozen area is not accessible, or if you can not thaw the pipe, call a licensed plumber." Utica goes further and says a qualified plumber should be called whenever a frozen pipe is suspected.

In practice, call right away if:

• The frozen section is inside a wall, ceiling or slab
• The whole house has no water and you can't find where the ice is
• You see or hear water leaking anywhere
• The pipe looks damaged, bulged or cracked

The same steps that prevent the first freeze prevent the next one. The Red Cross suggests letting cold water drip from a faucet served by exposed pipes when it's very cold, because running water "even at a trickle" helps prevent freezing. It also suggests opening kitchen and bathroom cabinet doors so warmer air reaches the plumbing, keeping garage doors closed, and holding the thermostat at the same temperature day and night.

For pipes that keep freezing, the Red Cross recommends pipe sleeves or UL-listed heat tape or heat cable. Utica adds that a heating cable should have "a built-in thermostat that turns the heat on when needed," and warns that "Heat tapes and cables will not work during power outages." It also suggests covering vulnerable pipes with foam or fiberglass insulation, "a minimum of 2 in (5.08 cm), the thicker the better." For the Phoenix version of this checklist, see can pipes freeze in Phoenix. If you'll be away during a cold stretch, the Red Cross says to leave the heat on, "set to a temperature no lower than 55° F."

If a pipe froze or burst, HQ Plumbing & Air repairs frozen and split lines across the Phoenix area, with 24/7 emergency service. We're licensed and insured.