At what temperature do pipes freeze?

Uninsulated pipes in unheated space began freezing at an outside temperature of 20°F in University of Illinois Building Research Council field tests. Wind through a gap in an outside wall can freeze a pipe above that, and pipes in heated rooms can hold out far colder.

Why does a dripping faucet stop pipes bursting?

It keeps the line open. A pipe bursts from pressure trapped between an ice plug and a closed tap. A drip lets that water escape, so the pressure never builds. Drip the cold tap fed by the exposed pipe.

What temperature should I leave the heat at when I go away?

The American Red Cross says no lower than 55°F. The other safe choice is to close the main shutoff and drain the lines. Water in the pipes with the heat off is the combination that fails.

How do I thaw a frozen pipe safely?

Keep the tap open and warm the pipe with a heating pad, a hair dryer or hot wet towels, working back from the tap. The Red Cross rules out blowtorches, kerosene or propane heaters and any open flame.

Is a frozen pipe covered in an empty house?

It depends on the policy and your state. The ISO specimen HO-3 excludes freeze damage while the house is vacant or unoccupied unless you kept the heat on or shut off and drained the water. Read your own form.

Why does the water show up after the cold has passed?

Ice can plug the split until it melts. When the pipe thaws, the break is open and the supply is live, so the leak starts hours after the coldest night. Be home, or have someone there, as it warms.

HyreRestore tools

Pipe freeze risk check

Three inputs: the forecast low, where the pipe runs, and whether the heat is on. Then the fix for each spot, and the order of steps if a pipe has burst.

20°F the temperature alert threshold for unheated pipes Building Research Council, University of Illinois field tests: uninsulated pipes in an unconditioned attic began to freeze at an outside temperature of 20°F, as summarized by South Carolina Farm Bureau Insurance, retrieved September 29, 2026.

Pipes in unheated space are at high risk when the forecast low reaches 20°F, and any pipe is at risk when the heat is off below freezing.

Building Research Council field tests put the onset of freezing in uninsulated attic pipes at 20°F. The pipe splits between the ice and a closed tap, which is why the American Red Cross says to drip the cold tap and remove outdoor hoses.

Your forecast and your pipes

Nothing is stored or emailed. If a pipe has burst, close the main first.

— Risk reading

— What to do now

— If it has already burst

What this assumed —

A forecast and a location, not a survey of your pipes. HyreRestore is not a plumber.

Why a pipe bursts somewhere other than the ice

Ice does not split the pipe where it forms. The split comes from pressure further along the line, and that is why a dripping tap helps.

What fails. Once ice blocks a pipe, more freezing pushes water toward the closed tap at the end. Pressure builds in that trapped section, between the ice and the tap, until the weakest point gives. Upstream of the ice, water can retreat toward the supply, so no pressure builds there.

Why a dripping tap works. An open tap gives the trapped water somewhere to go, so the pressure never builds. The drip is not about moving water fast enough to stop it freezing.

Why the water arrives later. A pipe that splits while full of ice can stay plugged until it thaws. When the ice melts, the split is open and the supply is live. If you suspect a freeze, have someone in the building as it warms up, and know where the main shutoff is before then.

The 20°F line. Building Research Council field tests at the University of Illinois found freezing began in uninsulated pipes in an unconditioned attic when the outside air fell to 20°F. Treat it as a trigger to act, not a promise: wind through a gap in an outside wall can freeze a pipe above 20°F.

Where pipes freeze, and the fix for each place

The American Red Cross names the same places: outdoor hose bibs, pipes in unheated basements, crawl spaces, attics and garages, and pipes in kitchen and bathroom cabinets.

Where	Why it freezes	The fix
Outdoor tap with a hose on	The hose holds water in the tap, so even a frost-free sillcock cannot drain back inside.	Remove and drain the hose, close the indoor valve that feeds the tap, open the tap to drain.
Crawl space	Unheated air, and open vents that let cold wind across the pipe.	Foam sleeves on the runs; close or cover vents in winter; listed heat cable on the worst sections.
Attic run above the insulation	The pipe sits in the coldest air in the house, outside the insulated envelope.	Move the run below the insulation where you can; otherwise insulate it and add listed heat cable.
Outside wall cavity	The pipe is indoors but on the cold side of the wall insulation.	Open the cabinet doors in a cold spell and drip the tap; reroute the run if the wall is ever opened.
Garage	Unheated space with a large door, and sometimes a water heater or laundry hookup.	Insulate the runs and connections; keep the garage door shut in hard cold.
Unheated basement	Cold air, and drafts at the rim joist where pipes come in.	Seal and insulate the rim joist and sleeve the pipes.
An empty house	No heat and nobody there, so a burst can run for days.	Heat on at 55°F or more with someone checking, or the main closed and the system drained.

The fixes are from American Red Cross frozen-pipe guidance and standard plumbing practice. We publish no prices for them.

Before the first freeze: six jobs, done once

None of these needs a contractor.

Take every hose off and drain the outdoor taps
The Red Cross lists it first: remove, drain and store hoses, close the inside valves that feed hose bibs, and open the outside bibs so they drain.
Sleeve the exposed runs
Foam pipe insulation on the pipe you can reach in crawl spaces, garages, attics and unheated basements.
Find the main shutoff and make sure it turns
Do it in daylight, before you need it at night with water coming through a ceiling. A valve that will not move is a job for a plumber now, not during a burst.
Seal drafts that reach the pipes
Crawl space vents, gaps where pipes enter, the edge of the garage door. Moving cold air freezes a pipe faster than still air at the same temperature.
Check attic pipes sit under the insulation
A pipe laid on top of the insulation is in the coldest air in the house. Fix it before winter.
If the house will be empty, choose: heat on, or drained
Heat at 55°F or more, or the main closed and the lines drained. Water in the pipes with the heat off is the risky middle, and the HO-3 specimen form excludes that freeze damage.

During a cold snap, in order

The American Red Cross gives these steps for very cold weather.

1
Drip the cold tap served by the exposed pipe
The tap at the end of the run you are worried about, not every tap in the house.
2
Keep the thermostat at one setting, day and night
Skip the overnight setback for the cold spell. If you are away, the Red Cross says to leave the heat no lower than 55°F.
3
Open kitchen and bathroom cabinet doors
Room air then reaches pipes on outside walls. Move cleaning products out of reach of children and pets first.
4
If a tap slows to a trickle, treat it as frozen
Leave that tap open and warm the pipe with a heating pad, a hair dryer or towels soaked in hot water, working from the tap back toward the cold section.
5
Never use an open flame
The Red Cross says no blowtorch, kerosene or propane heater, charcoal stove or other open-flame device. If you cannot find or reach the frozen section, call a plumber.

If a pipe has already burst

Safety and the shutoff come before anything else.

1
Close the main shutoff
Nothing else limits the damage while water is still coming in.
2
Keep away from wet electrics
If water is near outlets, the panel or a ceiling light, switch off at the breaker only if you can reach it without standing in water. If not, call the electric utility and stay out of that room.
3
Open the taps to drain the lines
Hot and cold. It empties the pipes so the break stops discharging what is left in them.
4
Photograph before anything moves
Wide and close, every room, and the broken section of pipe. The photos are the evidence for the claim and the estimate.
5
Tell your insurer and start drying
The HO-3 “Duties After Loss” ask for prompt notice and for you to protect the property from further damage. Both run at once: waiting for an adjuster before drying does not meet the second.
6
Get the water out and the drying started
The EPA puts it this way: “If wet or damp materials or areas are dried 24-48 hours after a leak or spill happens, in most cases mold will not grow.” The 24–48 hours run from the leak, not from when help arrives.
7
Keep the broken section of pipe
It shows a sudden break rather than slow corrosion, and sudden versus gradual is the line a homeowners policy draws on water damage.

Why a freeze in an empty house does more damage

A burst in an occupied house is found fast. In an empty one it can run for days before anyone sees it.

The size of the loss. A burst with nobody home keeps running at supply pressure until someone visits. The difference is a wet cabinet against ceilings, walls and floors soaked through.

The policy wording. The ISO specimen HO-3 (HO 00 03, 1991 edition) excludes freezing damage to plumbing while the house is vacant, unoccupied or being built, unless you used reasonable care to keep the heat on or to shut off the water and drain the system.

Your insurer may use a later edition or its own wording, so read yours.

Who it catches. Second homes, a house for sale after the owners moved out, a rental between tenants, and anyone away for weeks in winter. Turning the heat off to save money is the act that can take away the cover.

A cheap backstop. A low-temperature alarm or a leak sensor that alerts your phone works in exactly the case where nobody is there to notice. The prevention ROI calculator shows what a shutoff valve has to save to pay for itself.

What this check cannot tell you

The freeze check cannot see your pipes. It knows where you say they run and what the forecast is. Insulation, which side of it the pipe sits on, and drafts decide the outcome, and the check cannot see any of them.

20°F is a trigger, not a forecast of failure. How long the cold lasts and how much wind reaches the pipe matter as much as the low itself.

It cannot read your policy. Vacancy and heat conditions are in your own form and vary by insurer and state. HyreRestore is not a plumber, does not do restoration work and does not adjust claims.

Questions this calculator answers

At what temperature do pipes freeze?: Uninsulated pipes in unheated space began freezing at an outside temperature of 20°F in University of Illinois Building Research Council field tests. Wind through a gap in an outside wall can freeze a pipe above that, and pipes in heated rooms can hold out far colder.
Why does a dripping faucet stop pipes bursting?: It keeps the line open. A pipe bursts from pressure trapped between an ice plug and a closed tap. A drip lets that water escape, so the pressure never builds. Drip the cold tap fed by the exposed pipe.
What temperature should I leave the heat at when I go away?: The American Red Cross says no lower than 55°F. The other safe choice is to close the main shutoff and drain the lines. Water in the pipes with the heat off is the combination that fails.
How do I thaw a frozen pipe safely?: Keep the tap open and warm the pipe with a heating pad, a hair dryer or hot wet towels, working back from the tap. The Red Cross rules out blowtorches, kerosene or propane heaters and any open flame.
Is a frozen pipe covered in an empty house?: It depends on the policy and your state. The ISO specimen HO-3 excludes freeze damage while the house is vacant or unoccupied unless you kept the heat on or shut off and drained the water. Read your own form.
Why does the water show up after the cold has passed?: Ice can plug the split until it melts. When the pipe thaws, the break is open and the supply is live, so the leak starts hours after the coldest night. Be home, or have someone there, as it warms.

Sources and methodology

Figures dated September 29, 2026. Last reviewed September 29, 2026.

How Pipes Freeze and Burst (South Carolina Farm Bureau Insurance, retrieved September 29, 2026). The 20°F temperature alert threshold from Building Research Council field tests at the University of Illinois, and the pressure mechanism between the ice and a closed faucet.
Frozen Pipes (American Red Cross, retrieved September 29, 2026). Where pipes freeze; hoses; drip the cold tap; steady thermostat; heat no lower than 55°F when away; no open flame.
Homeowners 3, Special Form (HO 00 03 04 91, specimen) (Insurance Services Office, via Heritage Property & Casualty, retrieved September 29, 2026). The freezing exclusion while vacant or unoccupied, and Duties After Loss. Your insurer may use a later edition.
A Brief Guide to Mold, Moisture and Your Home (US Environmental Protection Agency, retrieved September 29, 2026). The 24–48 hour drying window.

Is it covered? How an HO-3 treats a sudden burst compared with slow leaks.
Should I file? The estimate against your deductible, before you call.
Prevention ROI calculator What a leak sensor or shutoff valve has to save.
Mold risk calculator Where wet materials stand against the 24–48 hour window.
Water damage restoration Water category and class, and what drying involves.
The first 24 hours Safety, the shutoff, photos and the claim, in order.

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