Quick answer
If a pipe is frozen but not burst: shut off water at the main (be ready in case it thaws and bursts), open the faucet fed by the frozen pipe, then thaw with a hair dryer starting at the faucet end and working back toward the freeze. Never use an open flame or propane torch — house fires cause more damage than burst pipes, and torches damage pipes. If the pipe has already burst, keep water off and call a plumber immediately.
Key facts
| Common causes | Uninsulated pipe in exterior wall; Pipes in unheated space; Pipe near air leak; Vacation/away with heat off |
|---|---|
| DIY difficulty | Moderate |
| Time to fix | 30–60 min |
| Parts cost | $0 parts |
| Tools needed | Hair dryer, towels, water main access |
| When to call a pro | If you can't locate the freeze · if pipe has burst |
What's happening
Water expands ~9% when it freezes. Trapped between the ice plug and a closed valve, that expanding water creates pressure that ruptures the pipe — usually not at the ice itself but at a weak spot elsewhere in the pipe. Once thawed, the burst releases dozens or hundreds of gallons per hour. The safe thaw sequence: (1) shut off main water first, (2) open a faucet on the frozen line so thawing water can flow out (releases pressure), (3) apply heat starting near the faucet and working back toward the freeze so water can escape as it melts.
Common causes (ranked by frequency)
- Uninsulated pipe in exterior wall 50% of cases
Pipes in poorly insulated exterior walls freeze first. Common in kitchens and bathrooms on the north side of the house.
- Pipes in unheated space 30%
Crawl spaces, attics, garages, basements. Any unheated area with plumbing is a freeze risk during cold snaps.
- Pipe near air leak 15%
A drafty area (poorly sealed rim joist, damaged siding) creates cold spots where pipes freeze even in insulated walls.
- Vacation/away with heat off 5%
House left with heat set too low (<55°F) during cold weather. Any plumbing can freeze.
How to diagnose
- Confirm the pipe is frozen, not just closed. Faucet doesn't work? Try another faucet on the same line. All faucets on that line dry = freeze somewhere in the line.
- Locate the frozen section. Feel accessible pipes for cold spots. Frost on the outside of a pipe = confirmed freeze location.
- Check for signs of a burst. Water on floor, hissing sounds, wet drywall = pipe already burst. Skip thawing and call a plumber.
- Have main water shutoff ready. Know where it is and confirm you can turn it.
The fixes
Fix #1 — Safe thaw with hair dryer Standard method
The safest thaw method. Slow, controlled, no fire risk.
Tools
- Hair dryer
- Old towels
- Bucket
Materials
- Shut off water at the main. Know where it is BEFORE this happens (usually in basement, crawl space, or utility closet near where water enters home).
- Open the faucet fed by the frozen pipe so thawed water can flow out (releases pressure).
- Start thawing at the faucet end and work back toward the freeze. This lets melt-water flow out; thawing the middle first can trap water and cause a burst.
- Apply moderate heat with hair dryer, moving continuously along the pipe. Don't concentrate on one spot.
- Watch for water flow at the faucet — a trickle means you're through the ice.
- Once flowing, keep dryer applied until pipe is warm to the touch throughout.
- Turn main water back on slowly and check the thawed area for leaks — any drip means the pipe cracked from the freeze.
Prevention
Insulate all pipes in unheated spaces with foam pipe insulation ($1–$3 per foot). During cold snaps: open cabinet doors under sinks on exterior walls, keep faucets on a slow drip (moving water resists freezing), leave heat set to at least 55°F when away. Long-term: seal air leaks around pipes (spray foam around pipe penetrations), consider heat tape on high-risk pipes.
When to call a pro
When to stop and call a pro
- Pipe has burst — water is actively leaking. Kill main water and call a plumber immediately.
- You can't locate the freeze — it's in a wall or ceiling.
- Multiple pipes are frozen simultaneously — indicates a larger heating or insulation problem.
- Pipe is in a wall or ceiling and inaccessible — professional infrared thawing equipment may be needed.
Emergency plumbing call for frozen/burst pipe: $300–$700. Pipe replacement per repair: $150–$400. Water damage restoration if flooding: $1,000–$10,000+.
Cost estimate
Cost estimate
Frequently asked questions
Two reasons: (1) house fires from thawing pipes with torches are one of the most common winter home fire causes, (2) direct flame can damage pipes and joints, causing leaks after thaw. Hair dryers are safer and only marginally slower.
Signs during or after thaw: water dripping from ceiling, wet drywall, hissing sounds, water pooling. If the pipe froze but you can't hear/see any leak after thawing and running water for 10 minutes, you probably caught it in time.
Yes — for faucets on exterior walls or in unheated areas. A slow drip prevents pressure buildup between an ice plug and a closed valve. Costs pennies in water; saves thousands in burst pipe damage.
Sustained outdoor temps of 20°F or below can freeze pipes in poorly insulated locations after 6+ hours. Well-insulated pipes in heated areas can survive much colder. The threshold depends more on wind, insulation quality, and duration than a specific temperature.