At what temperature do pipes freeze?

Pipes in unprotected spaces come under threat when outdoor temperatures drop to around 20°F, sooner with wind reaching the pipe. Interior pipes freeze when the space around them, not the thermostat's room, goes below freezing.

Should I let faucets drip in cold weather?

Yes, on runs served by vulnerable piping: a pencil-thin cold stream keeps water moving and relieves the pressure that actually bursts pipes. Open both hot and cold slightly, at the fixture farthest along the risky run.

How do I know if a pipe has frozen but not burst?

A single fixture or run delivering nothing or a trickle in freezing weather, with the rest of the house working, is the classic frozen-not-burst presentation. Thaw it with the tap open and watch the joints as flow returns.

Why do pipes burst when they freeze?

Usually not at the ice itself: the freeze seals the pipe, and pressure builds in the trapped water between the ice plug and the closed tap downstream. That pressure splits the pipe, often somewhere other than the frozen spot.

Frozen Pipes: Prevention and Safe Thawing

Page last reviewed: August 2026 · Reviewed by Harold R. Bennett, retired home inspector

Frozen pipes cause some of the most expensive ordinary damage a house can suffer, and nearly all of it is preventable with insulation, air sealing, and a few cold-night habits. Knowing how to prevent frozen pipes, and how to thaw one without making the news, is a cold-climate homeowner’s core curriculum. This guide covers the geography, the prevention hierarchy, and the thaw.

The geography of freezing

Pipes freeze where plumbing meets unheated air: crawl spaces and unconditioned basements, exterior walls (kitchen sinks on outside walls are the residential classic), attics carrying supply lines, garages with laundry plumbing, and the hose bibs that pass through the rim. Wind matters as much as temperature, since moving cold air strips heat far faster than still air, which is why the freeze often follows the drafty penetration rather than the coldest night. The bursting mechanism has a counterintuitive detail worth knowing: the ice plug seals the line, pressure builds in the water trapped between plug and closed tap, and the split happens wherever that pressure finds weakness, sometimes feet from the freeze, per the physics cousin of water hammer. Materials vary in tolerance, with PEX stretching where copper and CPVC split, per the piping comparison, but no material licenses neglect, since fittings and valves burst regardless.

Prevention, in order of permanence

Seal the cold out. The cheapest yard of progress: caulk and foam the penetrations where pipes, cables, and dryer vents pass through rim joists and exterior walls, and close crawl space vents for winter where design allows. A pipe in still 25°F air survives nights that the same pipe in a 25°F draft does not.

Insulate the pipe. Foam sleeves on every accessible run in vulnerable spaces, taped at the joints, with fittings wrapped rather than skipped. Understand what insulation does and does not do: it slows heat loss, buying hours, but insulated pipe in a persistently below-freezing space still freezes eventually.

Add heat where insulation is not enough. Thermostatic heat cable (heat tape), installed per its instructions and plugged into a GFCI, keeps chronic problem runs above freezing for pennies, the standard answer for crawl space mains and well lines. Opening cabinet doors under exterior-wall sinks on cold nights borrows room heat for free.

Manage the hose bibs. Disconnect hoses in fall, always, since a connected hose holds water in the bib and defeats even frost-free models; shut and drain interior stops feeding old-style bibs; and consider frost-free replacements at the next opportunity.

Cold-snap and travel habits. During severe cold: pencil-drip taps on vulnerable runs, doors open to circulate heat, garage door closed, thermostat never below 55°F. Leaving in winter: heat on, main shutoff closed with fixtures drained if the trip is long, and a neighbor or a leak-detection device keeping watch, since a burst discovered on day one and day ten are different insurance claims entirely.

Thawing without a disaster

A frozen-not-burst line, one fixture dead in freezing weather, gets thawed with method. Open the affected tap first, giving melt water and pressure somewhere to go. Locate the likely freeze by geography: the coldest accessible span on that run. Apply gentle heat, working from the tap back toward the freeze: hair dryer, heat gun on low kept moving, warm towels, or a space heater warming the whole cavity. Never open flame, which starts structural fires annually on exactly this errand, and never leave active heating unattended. Expect thawing to take patient minutes to hours, and watch the thawed run as pressure returns, because the burst, if there is one, reveals itself the moment the ice no longer seals it. A freeze inside a closed wall, or one you cannot locate, is a fair professional call, made better by shutting the main first.

When it has already burst

Water where it should not be, in freezing weather: main shutoff, immediately, which is the whole argument for knowing where it is; then power off to affected areas if water is near electrical; open taps to drain the system; and start drying while arranging the repair, since the mold clock and the moisture damage story start with the puddle, not the plumber.

The bottom line

Freeze risk is geography plus air movement: seal the drafts, sleeve the pipes, heat-tape the chronic runs, strip the hoses in fall, and drip the taps on the brutal nights. Thaw with the tap open and no flame, and keep the main shutoff in the household’s muscle memory, because the difference between a story and a claim is usually the first ninety seconds.