How to keep pipes from freezing and bursting
A burst pipe floods a house in minutes. Which pipes are at risk, why a dripping faucet helps, and what to do if one already froze.
A burst pipe is not a plumbing problem: it is a flood inside the house, usually when nobody is home or in the middle of the night. And the damage is not caused by cold itself but by pressure.
Why it bursts
When water freezes inside a pipe it forms a plug. The water between that plug and the closed faucet has nowhere to go, and pressure rises until the pipe gives way.
That is why the rupture often shows up in a section other than the frozen one, and why the fix is to give that pressure somewhere to go.
Where the at-risk pipes are
| Area | Why |
|---|---|
| Basements and garages | Unheated, with doors to the outside |
| Attics and dropped ceilings | Cold air above the insulation |
| Exterior walls | Little insulation between pipe and street |
| Hose bibs and irrigation | Exposed and holding water |
| Under sinks on exterior walls | Closed cabinet that gets no heat |
What to do before the cold arrives
- Insulate runs through unheated areas with foam or heat tape.
- Drain and disconnect garden hoses; shut off the irrigation valve.
- Put insulated covers on outdoor faucets.
- Open cabinet doors under sinks so warm air reaches the pipes.
- Locate the main shutoff and confirm it turns.
- If you will be away, do not set the thermostat below about 55 degrees.
If it already froze
- Open the faucet served by that pipe and leave it open.
- Apply gentle heat from the end nearest the faucet working back: hair dryer, warm towels or an electric heating pad.
- Keep going until flow returns to normal.
- Check the other pipes: if one froze, others are at risk.
If it bursts
Shut off the main valve immediately, then cut power to the affected area if water is near outlets or the panel. Photograph everything before you start drying: the insurer will ask.
- How to stay warm at home without power Shrinking the space, sealing the gaps and layering clothing beats any improvised heater. And the methods that kill people every winter.
- Ice storms: why they are the worst winter storm A quarter inch of ice can bring down a region's power grid for days. What makes freezing rain different from snow and how to get ready.
Gear that covers this
Products that match what the guide above recommends.
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Pipe insulation
Foam sleeves or heat tape on runs through unheated areas. The cheapest preventive measure and the one fewest people install.
- View on Amazon
Outdoor faucet covers
The hose bib is where the problem most often starts. A cover costs little and goes on in a minute.
Frequently asked questions
Why does a frozen pipe burst?
It is not broken by the ice where it forms but by the pressure that plug creates between it and the closed faucet. That is why the rupture often appears somewhere other than where the ice is.
Does leaving a faucet dripping help?
Yes. A continuous trickle relieves pressure inside the pipe and reduces the risk of rupture even if ice does form. Moving water also freezes more slowly.
Which pipes are most at risk?
Those running through unheated spaces: basements, garages, attics, crawlspaces and poorly insulated exterior walls. Also hose bibs and irrigation lines left with water inside.
How do I thaw a pipe without breaking it?
With gentle, gradual heat: a hair dryer or warm towels, starting at the end nearest the faucet, which should be left open. Never an open flame.