Frozen Pipes

Is It Actually Frozen?

Go turn on the other faucets. That one test tells you most of what you need to know.

A freeze is almost always local. One fixture gives you nothing, or a thin trickle that dies after a second, while the kitchen sink two rooms away runs at full pressure. The ice plug is sitting in the branch line feeding that one fixture, and it is sitting in the coldest run in the house.

Other things that confirm it:

• The low last night was below 32F and it stayed there for hours. Pipes do not freeze the minute the air hits freezing. It takes sustained cold. A night in the low 20s with wind moving through a vented crawlspace will do it to an uninsulated line.
• Frost or heavy condensation on an exposed section of pipe. Or the pipe is cold enough that it stings to keep your hand on it.
• Flow stopped overnight, not gradually. Freezing is sudden. A slow decline over weeks or months is a different problem: buildup, a valve, or a pressure issue.
• A visible bulge, or a section that looks swollen. That is bad news. Do not heat it. Skip to the shut-off part below.

If every faucet in the house is dry, it may still be a freeze, in the main line or in the line running from the well. But no water anywhere is also exactly what a failed well pump or a closed main valve looks like, so read no water from the well before you assume ice. And if you have water but it is cold everywhere, that is no hot water, not a freeze.

Where Pipes Freeze in Mountain Homes

Elevation is why this happens here and not an hour south. The same front that gives Atlanta a chilly night gives us a hard freeze. The spots that go first:

• Crawlspaces. Most homes around here have one, and most of them are vented, which means outside air moves freely under your floor all night. A pipe stapled to a floor joist in a vented crawlspace is outdoors as far as the cold is concerned.
• Exterior walls. A supply line run through the stud bay of an outside wall often ends up on the cold side of the insulation, with the batt behind it instead of in front of it. Room heat never reaches it.
• Unheated garages and utility rooms. Laundry hookups, utility sinks, and water heaters sitting in an unconditioned garage are common freeze points.
• Cabins and seasonal homes sitting empty. This is the worst case. Heat is off or set low, nobody is running water, and nobody is there to notice. A pipe can freeze, split, thaw, and pour for days before someone opens the door.
• Under sinks on an outside wall. Behind a closed cabinet door, on an exterior wall, those supply lines get almost no room heat.

Before You Touch It: It May Already Be Split

This is the part that catches people, and it is the reason the rest of this page is written the way it is.

Ice does not usually crush a pipe from the inside. Water expands about nine percent when it turns to ice, and that alone is not what splits copper or PEX. What splits the pipe is pressure. Once an ice plug forms and seals the line, water keeps freezing onto the back of that plug and pushes the water ahead of it down the pipe. If the faucet at the end is closed, that water has nowhere to go. It compresses in a sealed section between the ice and the closed valve, and pressure climbs until the weakest point in that run lets go.

Which means the split is usually not at the ice. It is somewhere between the ice and the closed faucet.

And it means this: the crack is already there before you start thawing. The ice plug is the only thing holding the water back. It is a cork. The second you melt it, pressure comes back and the split starts pouring, possibly inside a wall you cannot see.

So before you apply a single watt of heat, go find your main shut-off and confirm you can actually turn it. Not after. Before. If you have never located it, do that first. If it is seized, or you cannot find it, stop here and call. Have a bucket, towels, and your phone with you when you start. If water begins running, you want to be closing that valve in ten seconds, not hunting for it in the dark with a flashlight in your teeth.

How to Thaw It Safely

1. Open the faucet first. Both handles, hot and cold. This is not a detail and it is not optional. An open faucet vents the line, so pressure cannot build behind the ice. As the plug melts, the water and trapped air have a clear way out. You will also hear it when flow breaks through, which tells you that you found the right pipe.

2. Find the frozen section. Follow the line from the dead fixture back toward the water heater or the main and feel the pipe with your hand. The frozen stretch is noticeably colder than the rest and may have frost on it. In a crawlspace, check where the pipe passes a foundation vent or runs near an opening. That is usually it.

3. Apply gentle heat. A hair dryer is the standard tool and it works. So does heat tape rated for water pipes, an electric heating pad wrapped around the line, or a space heater aimed at a crawlspace section with sensible clearance from anything that burns. Move the heat back and forth over a foot or two of pipe rather than parking it on one spot.

4. Work from the faucet end back. Start at the fixture end of the frozen run and move toward the main, never the other way around. The reason is in the next section, and it is the single most important thing on this page.

5. Keep going after flow returns. When water comes back, you have melted a channel through the ice, not cleared it. There is still ice on the pipe walls. Keep heat on it and let the faucet run several minutes so the moving water finishes the job.

6. Then watch. Stay at the fixture, then walk the house. Check the ceiling under that run, the crawlspace below it, the cabinet floor. A split can take a few minutes to show itself. If you see water anywhere, shut the main off and call.

Why You Work From the Faucet End, Not the Middle

This is the mistake that turns a frozen pipe into a burst pipe.

Say you have a three foot section of ice. You find the middle of it, park a hair dryer there, and melt out the center. Now you have liquid water sitting between two ice plugs, one on each side of it. That pocket is sealed at both ends. It has no vent, because the open faucet you left running is on the far side of a plug that is still solid.

Water keeps melting off both plugs and adding to that trapped pocket. Pressure builds in a sealed section of pipe with nowhere to release. That is the exact mechanism that cracked the pipe in the first place, except now you are the one driving it, and you are driving it faster than the weather did.

Start at the faucet end and every drop of meltwater has an open path out of the fixture. The thawed section stays connected to open air the whole time. Pressure never builds. You push the ice back a bit at a time and it drains as you go.

Same reason the faucet stays open the entire time, even while nothing is coming out of it. Especially while nothing is coming out of it.

What Never to Put on a Frozen Pipe

• A propane torch, or any open flame. This has burned down houses. Framing, insulation, and vapor barrier catch well before the ice gives up, and in a crawlspace you are in a confined space full of dry material with a flame pointed at the underside of your floor. A torch also heats copper fast enough to flash the trapped water to steam and turn a hairline split into a rupture.
• A torch on PEX or CPVC. Plastic supply line does not survive it. You will melt straight through the pipe.
• Boiling water poured over the pipe. It cools on contact, it goes everywhere, and it does nothing a hair dryer will not do better and drier.
• Anything left unattended. Do not tape a heating pad to a pipe and go to bed. If that line is split, you want to be awake and standing next to it when it opens up.

Frozen Pipe Questions

How long does it take to thaw a frozen pipe?

With a hair dryer on a pipe you can see and touch, 30 to 45 minutes is normal for a typical branch line. A long run, a pipe inside a wall, or a hard freeze that had all night to work can take several hours. If you have held steady heat on an accessible pipe for over an hour and nothing has changed, you are probably not on the frozen section. Move along the line and keep feeling for the cold stretch.

Will a frozen pipe thaw on its own?

Yes, once the air around it climbs back above freezing and stays there. The problem is that you do not control the timing. If the pipe is split, it starts pouring the moment it lets go, and you want to be standing there when that happens instead of at work. If you are leaving the house, shut the main off before you go.

Why do frozen pipes burst after they thaw instead of while frozen?

The split happens while the pipe is frozen, from pressure trapped between the ice plug and a closed faucet. But that same ice plug is a cork. It blocks the flow, so nothing comes out of the crack. When the ice melts, the cork is gone, pressure returns, and the water finds the split. That is why the flood shows up on the warm-up and not during the freeze.

Should I leave my faucets dripping?

During a hard freeze, yes. Moving water is much harder to freeze, and an open faucet keeps pressure from building behind any ice that does form. But that is prevention, and it only helps before the plug forms. If flow has already stopped, dripping will not thaw anything. For the full before-the-freeze list, read how to winterize your pipes.

How much does frozen or burst pipe repair cost?

Emergency plumbing generally runs about $500 to $2,000. Where it lands depends on where the pipe is and what has to come apart to get to it. An accessible crawlspace repair is on the low end. A split inside a finished wall or ceiling is on the high end, because the access is most of the work. The estimate is free.