What should I do if a pipe in my house freezes?

Twenty degrees Fahrenheit is the number to watch. SharkBite's winterizing guidance, citing the Building Research Council at the University of Illinois, treats 20°F outside as the alert threshold for uninsulated pipes, especially in Southern homes never built for a hard freeze.

If a faucet on an outside wall coughs out a trickle the morning after a cold night, you probably have ice in that branch. The question that decides your next hour is whether the pipe has already split.

First, check for water before you check for ice

Trace the pipe you can see from that faucet back toward where it enters the house: under the sink, through the basement or crawl space, along the garage wall. Look for water on the floor, a stained ceiling below, and a pipe or fitting that looks bulged.

Flat rule: if you find any of those, shut the main water valve before you do anything else. A split pipe often doesn't leak while it's frozen, because the ice plugs the crack. It starts leaking as it thaws, at full house pressure. Find your main shutoff now, not when water is coming through a light fixture.

Then call a licensed plumber.

Thawing an exposed pipe: open the faucet first

Open the faucet the frozen branch feeds before you add any heat. Melting ice needs somewhere to go, and running water speeds up the thaw. SharkBite's guidance gives the same reason for dripping a faucet in a cold snap: moving water relieves pressure in the line and keeps ice from forming a blockage.

Work only on pipe you can see and reach from the floor. Use gentle heat: a hair dryer kept moving, warm damp towels, or a space heater kept well clear of anything that burns and never left running unattended. Keep any corded tool out of standing water and plug it into a GFCI-protected outlet.

Never use a torch, a heat gun on high, or any open flame. The International Code Council's winter safety guidance warns that deadly fires can result when homeowners use torches to thaw frozen pipes. Framing, insulation paper, and dust sit inches from most supply lines.

Stop and call a plumber if the frozen section runs inside a wall, ceiling, or floor, sits next to a gas line or electrical panel, or a few minutes of warming brings no water back.

Heat cable is not a thawing tool. The Wrap-On pipe heating cable installation sheet says plainly that the cable isn't designed or able to thaw frozen pipes. It's for prevention only.

The spring surprise: the outdoor faucet

A frost-free sillcock, the long-stem outdoor faucet, puts its actual shutoff valve back inside the heated wall; Woodford builds its residential models for wall thicknesses from 4 to 24 inches. When you close it, the water in the stem drains out the spout. That only works if the spout can drain.

Woodford's documentation for its Model 17 freezeless faucet says it won't rupture from freezing when the valve is closed and the hose is removed. Woodford's troubleshooting guide lists a hose left attached as a cause of burst faucets. The hose traps water in the stem, the stem freezes, and the split sits inside your wall where you can't see it. You find out in April, the first time you turn the handle and water runs into the basement instead of the garden.

Woodford's limited warranty covers defects for one year and excludes misuse contrary to the instructions, which a hose left on through a freeze is hard to argue against.

Flat rule: hoses come off every outdoor faucet before the first night below freezing. It's the cheapest freeze protection in the house.

Prevention that actually works, by how cold the pipe gets

The International Residential Code doesn't let a builder leave pipes exposed to freezing. IRC Section P2603.5 says water pipes can't go outside the building, in attics or crawl spaces, or inside exterior walls unless they're protected by insulation, heat, or both. That's a performance standard, so a house can pass and still have one run that freezes every January. The ICC's own guidance is to keep supply piping out of exterior walls and unconditioned spaces in high-freeze areas when you can.

Here's what each layer does:

• Foam pipe insulation slows heat loss but doesn't add heat. On a pipe in a crawl space that sits below freezing for days, insulation alone only delays the freeze.
• Thermostat-controlled heat cable adds heat. Emerson's EasyHeat freeze-protection cable switches on at 38°F and off at 45°F, plugs into a standard 120-volt outlet, and must be GFCI protected. Frost King's automatic kits run at 7 watts per foot in lengths from 3 to 30 feet. The Wrap-On instruction sheet says the cable won't keep a pipe from freezing unless the pipe is insulated, and that the cable can't overlap itself or pass through a wall, floor, or roof. Follow the sheet in the box exactly; the UL listing covers only the uses it describes.
• Dripping faucets during a cold snap. SharkBite's guidance is to start dripping faucets on exterior-wall pipes when the forecast drops to 28°F or below, and to keep the thermostat no lower than 55°F, including when you're away.

Flat rule: if the same pipe freezes twice, stop treating it as bad luck. Insulate it and add heat cable if it's exposed. If it's buried in an exterior wall, get a plumber to price rerouting it into heated space.

Does pipe material save you?

Partly. Uponor says its PEX-a tubing can expand up to three times its diameter without cracking and survived more than 400 freeze-thaw cycles in its testing. SharkBite, which also sells PEX, says PEX can still burst in extreme conditions. Copper and CPVC have no such margin, and fittings and valves don't stretch on any material. Plan around the freeze not happening.

What the repair costs, and what changes the bill

There's no honest single price for a burst-pipe repair. What you'll pay depends mostly on access, not on the pipe. On an exposed copper line in an unfinished basement, a plumber can often cut out the split and close the gap with one push-fit repair coupling. SharkBite says its Max slip coupling replaces up to 2 inches of damaged pipe with a single fitting, and its standard brass slip couplings are rated to 200 psi. That's a short visit. A split behind finished drywall adds demolition, drying, and patching, and the drywall work usually costs more than the plumbing.

The Bureau of Labor Statistics puts the median annual wage for plumbers, pipefitters, and steamfitters at $62,970 as of May 2024. That's what the plumber earns, not the rate you're billed, and after-hours calls during a regional cold snap usually cost more than a scheduled visit.

If you're away for long stretches in winter, or a burst would land on a finished ceiling, an automatic shutoff valve is the backstop. Moen's Flo installs on the main line after the meter and pressure regulator. It sends freeze alerts and closes the main when it sees abnormal flow. Moen's web price is $599.99 for the ¾-inch model, $649.99 for 1-inch, and $1,039.99 for 1¼-inch, before installation. It won't stop a pipe from freezing. It limits how much water gets out after one splits.

Research sources

• ICC Digital Codes: 2021 International Residential Code, Section P2603.5 Freezing
• ICC: Build It to Code to Minimize Damage from Frozen Water Pipes
• ICC: Winter Safety Resources
• BLS Occupational Outlook Handbook: Plumbers, Pipefitters, and Steamfitters
• SharkBite: Winterizing Tips, 6 Ways to Help Your Customers Prevent Frozen Pipes
• SharkBite: How PEX Pipe Performs in the Winter
• SharkBite: Fix Frozen Pipes, Burst Pipe Repair
• SharkBite: Brass Push-to-Connect Slip Couplings
• Uponor: Freeze Resilience of Uponor PEX-a Pipe
• Woodford: Model 17 Freezeless Faucet
• Woodford: Model 17 Troubleshooting Guide
• Woodford: Residential Wall Faucets Brochure
• Woodford: Residential Wall Faucets Specifications
• Woodford: How a Standard Frost-Proof Faucet Works
• Emerson Appleton: EasyHeat Heating Cable Catalog
• Frost King: Automatic Electric Heat Cable Kits
• Wrap-On: Pre-Terminated Pipe Heating Cable Installation Instructions
• Moen: Flo Smart Water Monitor & Shutoff, 0.75"
• Moen: Flo Smart Water Monitor & Shutoff, 1.00"
• Moen: Flo Smart Water Monitor & Shutoff, 1.25"