At What Temperature Do Pipes Freeze? The 20°F Rule and Risks
At what temperature do pipes freeze? Exposed pipes can freeze when the outdoor temperature stays near 20°F (-7°C) for hours. See the risk table.
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** Water freezes at 32°F (0°C), but pipes inside a heated home are protected. Uninsulated pipes in outside walls, attics, crawl spaces or garages can start to freeze when the air around them stays at about 20°F (-7°C) or lower for several hours, and sooner in a strong wind. The risk grows with each hour of cold.
The risk grows with each hour of cold.
At what temperature do pipes freeze: the short answer
There is no single number, because pipes freeze when heat loss beats the heat they receive. As a general rule, the danger zone is outdoor air near 20°F or below for several hours. Pipes in exterior walls, unheated spaces and outdoor faucets can freeze at higher temperatures when wind drives cold through gaps.
| Quick facts: at what temperature do pipes freeze | |
|---|---|
| Water freezes | 32°F (0°C) |
| Risk of freezing in exposed pipes | Around 20°F (-7°C) or colder for several hours |
| Faster freezing | Wind, drafts, uninsulated walls, thin or exposed pipes |
| Biggest danger | A frozen pipe that splits as the ice expands and thaws |
What changes the risk
| Factor | Effect |
|---|---|
| Insulation | Slows heat loss; uninsulated pipes freeze sooner |
| Location | Exterior walls, attics, crawl spaces and garages are the worst |
| Wind | Pushes cold air through gaps and speeds freezing |
| Duration | Several hours of deep cold is worse than a brief dip |
| Pipe material | Metal conducts cold quickly; PEX tolerates some freezing better |
| Water flow | Moving water freezes less easily than still water |
| House heat | Low indoor heat lets cold reach the walls |
Where pipes freeze first
Outdoor hose bibs and the pipes behind them, pipes along the north side of the house, kitchen and bathroom plumbing on exterior walls, pipes in unheated garages, crawl spaces and attics, and any line near a vent, a gap or a cold draft are the usual victims.
Signs a pipe is freezing
- A faucet runs with only a trickle or no water.
- Frost on exposed pipes.
- A cold spot on a wall or pipe.
- Odd smells from the drain, if the drain line is partly frozen.
- Banging or strange noises as water tries to pass.
How to prepare when it gets cold
Open cabinet doors under sinks so warm air reaches the pipes. Let a faucet drip on the coldest nights. Keep the thermostat at 55°F or higher, even if you are away. Disconnect and drain outdoor hoses and shut off water to outdoor faucets. Insulate exposed pipes and seal drafts. Know where your main shutoff is, so you can use it fast if a pipe bursts.
What to do if a pipe freezes
Open the faucet, apply gentle heat with a hair dryer or warm towels, starting near the faucet and moving toward the frozen part, and never use an open flame. Turn the water back on slowly and check for leaks. If you cannot find the frozen section or the pipe is split, shut off the main water supply and call a plumber.
How long does it take
Freezing can occur within a few hours in severe cold on an exposed pipe, and much longer in a well-insulated wall. A pipe can be frozen but not yet burst, so check promptly after a cold night.
At what temperature do pipes freeze in different regions?
In mild climates, a single cold night can catch homeowners out because the pipes are rarely insulated, so a dip to the mid-twenties can be enough to cause trouble. In cold climates, builders place pipes in heated walls, and trouble is more likely during extreme cold or when the heat fails. Either way, the question of at what temperature do pipes freeze is best answered with a margin: act when the forecast shows hours below freezing, not minutes.
Use the forecast
Watch the overnight low, the wind chill and how many hours the temperature stays below 25°F. A short dip is far less dangerous than a long cold night. Take simple steps by the afternoon before the cold arrives.
When to call a professional
If you hear running water inside a wall, see a stain spreading, find a split pipe or cannot thaw a line safely, call a plumber. Knowing at what temperature pipes freeze helps you act before the cold arrives, not after.
Related reading
- What temperature does pipe burst: What to Do First
- How to Thaw Frozen Pipes Safely: 6 Steps and What to Avoid
- Does frozen pipe always burst: What to Do First
- How to prevent burst pipe: A Step-by-Step Guide
Browse all plumbing guides, or find a plumber in your city from the plumbing directory.
Frequently asked questions
At what temperature do pipes freeze?
Water freezes at 32°F, but pipes in heated spaces are protected. Exposed or uninsulated pipes can start to freeze when the air around them stays at about 20°F (-7°C) or lower for several hours, sooner in wind.
How long does it take for pipes to freeze?
In severe cold, an exposed or uninsulated pipe can freeze within a few hours. In an insulated wall with house heat, it can take much longer. Wind and gaps speed it up, so risk depends on conditions as well as temperature.
Will pipes freeze at 25 degrees?
They can if the pipes are exposed, uninsulated or in a drafty area and the cold lasts for hours. Pipes in a heated, insulated part of the house usually do not. Outdoor faucets and unheated spaces are the usual victims.
Do pipes freeze at 32 degrees?
Rarely at first. Water freezes at 32°F, but pipes inside a house have heat around them and insulation, so freezing usually needs sustained colder temperatures. Exposed pipes outdoors can freeze near 32°F in wind.
Which pipes freeze first?
Outdoor hose bibs, pipes in exterior walls, in attics, crawl spaces and garages, and lines near drafts or vents. Pipes on the north side of the house and those with little insulation are most likely.
How do I keep pipes from freezing when it is cold?
Open cabinet doors, let a faucet drip, keep the thermostat at 55°F or higher, insulate exposed pipes, seal drafts and disconnect and drain outdoor hoses. Know where the main shutoff is in case a pipe bursts.
At what temperature do pipes freeze and burst?
Pipes usually split when the water has frozen and the ice expands, often noticed after thawing. That can follow several hours near or below 20°F, and the leak shows when the ice melts and water flows.
Does dripping a faucet really prevent freezing?
It helps. Moving water freezes less easily and a drip relieves pressure if ice does form. It is not foolproof, so combine it with insulation, warmth and open cabinet doors on the coldest nights.
What should the thermostat be set to in freezing weather?
Keep it at 55°F or above, even when you are away, so heat reaches exterior walls and the pipes inside them. Lower settings risk freezing, especially in older or poorly insulated houses.
When should I call a plumber about frozen pipes?
Call if you cannot find the frozen section, the pipe is split, water is leaking, or the line is inside a wall. Shut off the main water supply first if there is any sign of a burst.
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