How to Thaw Frozen Pipes (Before One Bursts)
Hair dryer plus 30 minutes fixes most frozen pipes. Learn how to thaw frozen pipes safely, spot burst damage early, and skip the $5,000 insurance claim.
Quick answer: Shut off the main water supply, then open the nearest faucet before you apply heat. Work from the faucet toward the frozen section with a hair dryer or electric heating pad. Never use an open flame. Most residential frozen pipes thaw in 20 to 60 minutes. If the pipe is inside a wall or has already burst, skip the DIY and call a plumber.
A frozen pipe is one of those situations where the clock matters. Pipes that freeze and sit for hours are more likely to split than ones you catch early. The difference between a 30-minute hair-dryer fix and a $5,000 water-damage claim often comes down to whether you got to it before it let go.
The Insurance Institute for Business and Home Safety puts the average burst-pipe insurance claim at right around that number. The intervention cost when it’s still frozen: nothing if you own a hair dryer, maybe $25 if you need a pipe heating cable afterward.
Here is how to do it without making it worse.
What You’ll Need
Tools:
- Hair dryer (the go-to for most accessible pipe runs)
- Electric heating pad or heat lamp (better for tight spaces)
- Flashlight
- Bucket and rags
Supplies:
- Foam pipe insulation, roughly $1-2 per linear foot at any hardware store
- Pipe heating cable, $25-40 for a 6-foot section, for pipes in unheated crawl spaces or against exterior walls
You do not need a heat gun for most residential copper or PEX pipe. A standard hair dryer on the high setting puts out enough heat. Heat guns run at 500°F to 1,100°F depending on the setting, which is harder to control near wood framing or plastic fittings.
Step 1: Find the Frozen Section
The vulnerable spots are predictable: an exterior wall, an unheated crawl space, under a cabinet on an outside wall, or where the pipe passes through an uninsulated section of framing.
Run the faucet fed by the suspect pipe. No water or just a trickle means the blockage is somewhere between the main line and that tap. Trace the pipe back from the faucet with your hand. The pipe feels noticeably colder at the frozen section, sometimes with visible frost on copper.
PEX pipe has enough flex that it can partially bulge before cracking, which buys a little more time than rigid copper. That said, PEX fittings are less forgiving than the pipe itself, so check the connections carefully once it’s thawed.
Step 2: Shut Off the Water Supply
Before applying any heat, turn off the main shutoff valve. If the pipe already has a hairline crack somewhere you have not found yet, you want flow stopped before it turns into a flood once the ice melts.
If you’re not sure where your main shutoff is, it’s usually near the water meter, in a basement or utility closet, or on an exterior wall near where the main line enters the house. We have a full walkthrough on how to shut off the water to your house if you need it.
Step 3: Open the Faucet
Open the faucet the frozen pipe feeds, both handles if it’s a sink or tub. This does two things: it relieves pressure in the pipe as the ice starts to melt, and it gives you a live indicator of when the blockage has cleared. Water will start running intermittently once the thaw is working.
Do not skip this step. A sealed pipe with heat applied can build pressure as steam forms at the thaw point. Opening the faucet keeps that pressure from concentrating at the same spot where the pipe is already stressed.
Step 4: Apply Heat to the Pipe
Work from the faucet end toward the frozen section, not from the wall inward. That way, any meltwater has an open path to escape rather than pooling behind the thaw point.
Hold the hair dryer six to eight inches from the pipe and move it slowly back and forth. Copper conducts heat well and warms through in a few minutes of steady attention. PEX takes a bit longer because it insulates against heat rather than spreading it.
For pipes in tight corners or inside a cabinet, an electric heating pad wrapped around the pipe works better than trying to angle a hair dryer in. For a pipe exposed to a crawl space or exterior wall overnight, a heat lamp aimed at the area for 30 to 45 minutes is easier than holding the dryer the whole time.
What to avoid:
An open flame is off the table. Propane torches have caused house fires when used near wood framing or insulation. This applies to PEX in particular, which will melt. Even on copper, a torch heats unevenly and can anneal fittings, weakening the solder joints over time.
Boiling water poured directly on the pipe creates thermal shock. Cold copper or cast iron hit with boiling water can crack at the stress point. Warm water applied with a cloth works in a pinch, but a hair dryer is safer and more controllable.
Step 5: Restore Water Flow and Check for Damage
Once water flows steadily from the open faucet, turn the main supply back on slowly. Watch the previously frozen section for 10 minutes. Even a hairline crack will show itself quickly once pressure is restored.
Look for discoloration on walls or ceilings near the pipe run, dampness on framing, or water on the floor in the crawl space. A cracked pipe often drips slowly and may not be obvious at first.
If everything looks dry, wrap the vulnerable pipe section with foam pipe insulation before the next cold snap. The American Red Cross recommends keeping at-risk pipes above 55°F during cold weather, which typically means opening cabinet doors under exterior sinks and letting faucets drip slightly during extreme cold. The full guide on how to prevent pipes from freezing covers all of it.
For anything involving low or inconsistent water pressure after the thaw, check our rundown on why water pressure drops. A partial crack can restrict flow without spraying obvious water.
Common Mistakes
Using an open flame. The speed temptation is real when you’re crouched in a cold crawl space. A hair dryer is slower. It also doesn’t start fires.
Not opening the faucet first. Seems like a small detail. The whole thawing process works better with pressure relief, and skipping the faucet concentrates stress at the thaw point where the pipe is already under strain.
Thawing only the visible section. If a pipe froze in one spot, the conditions that caused it probably affect more of the same run. Work through the entire accessible length, not just the frost you can see.
Calling it done and walking away. Check back in an hour. Hairline cracks leak slowly and are easy to miss during the initial inspection.
When to Call a Pro
Call a plumber if:
Water is already spraying or pooling. Shut off the main supply immediately and call. At that point the pipe has burst and needs replacement, not thawing.
The frozen section is inside a wall cavity. Getting heat to it without opening the wall requires specialized pipe-thawing equipment that plumbers carry.
Multiple fixtures have no water. That means the freeze is on the main line or in a section serving most of the house. That is not a hair-dryer job.
Water pressure came back low or uneven after the thaw. A partial burst can restrict flow without obvious spray. Have a plumber inspect it before another hard freeze hits.
FAQ
How long does it take to thaw a frozen pipe? Most accessible residential pipes thaw in 20 to 60 minutes with a hair dryer. A pipe frozen solid over several inches in a cold crawl space can take longer, up to two hours with a heat lamp. If it’s been frozen since the previous night and you can’t reach it, a plumber with a pipe-thawing machine is the right call.
Will a frozen pipe always burst? No. Pipes can freeze and thaw multiple times without cracking, particularly PEX, which has more give than copper. That said, repeated freeze-thaw cycles work-harden copper fittings and stress solder joints over time. A pipe that keeps freezing in the same spot needs insulation or a heating cable on that section.
What temperature do pipes freeze at? The Insurance Institute for Business and Home Safety found that pipes in unheated or poorly insulated spaces start to freeze when outdoor temperatures drop to 20 degrees Fahrenheit for six or more hours. Pipes against an exterior wall are more vulnerable than pipes running through conditioned interior space, which is why the cabinet-door trick works as well as it does.
Can I use a heat gun instead of a hair dryer? A heat gun works, but it runs much hotter. Use the lowest setting and keep it moving constantly. For PEX pipe, stay with a hair dryer. Heat guns are more useful on accessible copper runs in unfinished spaces where you are not working near wood framing.
How do I know if a pipe is about to burst? Signs of imminent failure: the pipe is visibly bulging (most common with PEX), there is a small pinhole spray starting, or you hear a cracking sound when heat is applied. At the first sign of any of these, turn off the main supply and call a plumber.
Can I thaw a pipe inside a wall? Sometimes. If you know where the pipe runs and there is no insulation between the drywall and the pipe, a heat lamp aimed at that wall section for 30 to 45 minutes can transfer enough warmth to thaw it. This is slow and not always effective. For a pipe deep in an insulated wall cavity, a plumber with pipe-thawing equipment is the right tool.
How do I keep it from freezing again? Foam pipe insulation on the vulnerable section is the fastest fix. A pipe heating cable plugged into a standard outlet handles the worst cases in unheated spaces. Keeping cabinet doors under exterior sinks open during hard freezes helps more than most people expect. The prevention guide covers all three approaches in detail.