Will My Pipes Freeze Tonight?

Enter your zip code, and this free tool reads the National Weather Service hourly forecast for your area. It shows the lowest temperature in the next 48 hours, how many of those hours fall at or below freezing, and a plain verdict on the risk to your pipes, with what to do before bed.

How the Freeze Risk Is Calculated

The tool finds a representative point for your zip code in the Census Bureau's ZIP Code Tabulation Area file and gets the National Weather Service (NWS) hourly forecast there. It takes the coldest hour in the next 48 hours and counts all the hours at or below 32°F in that window; they don't have to be in a row.

32°F is water's freezing point, and the NWS defines a freeze as 32°F or below. The mid-30s caution is based on the NWS: frost often forms with thermometer readings in the mid-30s, because the ground and objects on it can cool below the air.

20°F is the "temperature alert threshold" that 1996 University of Illinois Building Research Council research proposed for the southern US. In its attic field tests, an uninsulated pipe laid above the attic insulation, about as vulnerable as a pipe in a house can get, the researcher wrote, started to freeze whenever the outdoor temperature fell just below 20°F. The same research expected occasional freezes between 20°F and 32°F, especially where holes in the house's shell let cold air reach a pipe. Texas A&M AgriLife Extension and State Farm use the same figure. It was meant for places where freezing weather is the exception; where homes are built for cold, treat it as the cue to check the pipes you know are vulnerable.

12 hours is our judgment call, not a figure from any source. Published figures vary: Hanover, an insurer, says interior pipes left unused at 20°F can freeze in about 4 hours, while in the Illinois freezer tests an insulated half-inch pipe in 20°F air took about 11½ hours to block with ice. The NWS describes a freeze as lasting a "climatologically significant" or "extended" period without giving a number of hours. The longer the cold lasts, the further an attic, crawl space, or garage cools; 12 hours is about a whole night. At 20°F or colder, the tool raises its alert however long the cold lasts.

Not counted: wind chill, which the NWS says applies only to people and animals; wind cools a pipe to the air temperature faster, but never below it. The tool also ignores the NWS's 28°F hard freeze, which is defined by its effect on plants. And a forecast can't see inside your walls, so weigh the verdict against what you know about your house.

What Temperature Do Pipes Freeze At?

Water freezes at 32°F, but most pipes don't freeze the moment the outdoor air reaches 32°F. Keeping the heat on holds indoor plumbing above freezing, which is why the Red Cross and the Insurance Institute for Business & Home Safety (IBHS) set a 55°F minimum. The pipes that freeze are the ones the heat doesn't reach. The Red Cross lists them:

• pipes exposed to severe cold, such as outdoor hose bibs and pool and sprinkler supply lines;
• supply pipes in unheated interior areas: basements, crawl spaces, attics, garages, and kitchen cabinets;
• pipes that run against exterior walls with little or no insulation.

An unheated attic usually stays a few degrees warmer than outdoors, and water can cool several degrees below 32°F before ice forms, which helps explain why the Illinois attic pipes held out until about 20°F. Insulation keeps those spaces warmer. Wind pushes cold air through cracks and gaps, and pipes exposed that way, or in walls without insulation, can freeze above 20°F; pipes outdoors can freeze at any temperature below 32°F. Duration matters too: a few hours just below freezing is not a day that never thaws.

The 1996 Illinois study found burst pipes a more severe problem in the South than in the North, and IBHS notes that older homes, especially in Southern states, are more likely to have inadequate insulation.

What to Do Tonight

At a brief freeze, protect hoses, outdoor faucets, and anything exposed to outside air. At a long freeze or a pipe-freeze alert, do all of this before bed.

• Drip faucets on vulnerable pipes. Let cold water drip from faucets on exterior walls or served by exposed pipes. Even a trickle helps keep the pipe from freezing, the Red Cross says, and the NWS notes that an open faucet relieves the pressure that builds between the faucet and an ice blockage. In extreme cold, IBHS and the CDC say to let every faucet drip.
• Open the cabinet doors under kitchen and bathroom sinks, especially on exterior walls, so room air reaches the pipes, as the Red Cross, IBHS, and CDC advise. Move cleaners and chemicals out of reach of children and pets first.
• Hold the thermostat steady, at the same temperature day and night. If you are away, keep the heat no lower than 55°F.
• Disconnect hoses and drain them. If an outdoor faucet has an inside shutoff valve, close it, then open the outdoor faucet to drain the line and leave it open. Keep the garage door closed if water lines run through it. Our outdoor faucet guide covers the full job.
• Know where your main shutoff is, and make sure it turns, so you can close it fast if a pipe splits. Our main shutoff guide shows where to look.
• Never thaw a pipe with an open flame. If one freezes anyway, use gentle heat (see below). For a pipe that freezes every winter, our heat tape guide covers the lasting fixes.

If a Pipe Already Froze

If a faucet gives only a trickle, suspect a frozen pipe. Keep the faucet open, find the main shutoff, and check for splits before applying heat; our frozen pipes guide walks through safe thawing. If a pipe has split or water is coming through a wall or ceiling, shut off the main and follow our burst pipe guide.

Frequently Asked Questions

Will pipes freeze at 28 degrees?

It depends on where the pipe is. Hoses, outdoor faucets, and pipes directly exposed to outside air can. Pipes in unheated spaces are less likely to freeze at 28°F than at the 20°F alert threshold, but drafts, missing insulation, or a long cold stretch raise the risk. Pipes inside the heated part of the house, away from exterior walls and outside-wall cabinets, stay above freezing while the heat stays on.

How long does it take pipes to freeze?

There's no dependable number. It depends on how cold the pipe's surroundings get, its insulation, whether water is moving, and how much cold air gets in. Published figures vary: Hanover, an insurer, says interior pipes left unused at 20°F can freeze in about 4 hours. In the University of Illinois freezer tests, an insulated half-inch pipe took about 11½ hours to block with ice at 20°F, 6½ hours at 10°F, and 4¾ hours at 0°F. Wind makes an exposed pipe reach the air temperature sooner, the NWS says, but never colder. That is why the tool counts the hours at or below 32°F, and raises its alert at 20°F however long the cold lasts.

Should I drip faucets at 20 degrees?

Yes. The Red Cross says to let cold water drip from faucets served by exposed pipes, so at minimum drip faucets on exterior walls or served by pipes in unheated spaces. IBHS and the CDC go further and say to let every faucet drip in extreme cold, and 20°F is the research-based alert threshold. Even a trickle helps, the Red Cross says.

Do pipes freeze in a heated house?

Yes, where pipes run beyond the heat's reach: exterior walls with little insulation, sink cabinets on outside walls, crawl spaces, unheated basements, attics, garages, and where the water line enters through the foundation. IBHS adds that a power outage or a broken heating system can leave a home cold enough for pipes to freeze. If the power goes out, never heat the house with a stove, oven, grill, or generator.

The Bottom Line

Water freezes at 32°F, but pipes freeze where the heat doesn't reach. At or below 32°F, protect hoses, outdoor faucets, and exposed pipes. When 12 or more of the next 48 hours are at or below freezing, or the low hits 20°F, also drip vulnerable faucets, open sink cabinets, hold the thermostat steady (55°F minimum when away), and know your main shutoff. Thaw a frozen pipe gently, never with a flame.

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