At what temperature do pipes freeze?

What the code says, and what nobody says

Two things have to happen before a pipe bursts. The water in it has to freeze, and the ice has to keep expanding until the pressure in the closed section exceeds what the pipe can hold. Water starts that process at 32°F, but a pipe is not sitting in open air at the temperature on your phone. It sits in a cavity buffered by the building around it, sometimes insulated, often carrying water that is still moving.

The plumbing code handles that uncertainty by regulating placement rather than predicting failure. IRC Section P2603.5 reads: In localities having a winter design temperature of 32°F (0°C) or lower as shown in Table R301.2 of this code, a water, soil or waste pipe shall not be installed outside of a building, in exterior walls, in attics or crawl spaces, or in any other place subjected to freezing temperature unless adequate provision is made to protect it from freezing by insulation or heat or both. IRC Section P2603.5, Freezing (2021 edition). In other words the trigger is a 32°F winter design temperature, and the remedy is insulation or heat rather than a promise about a particular night.

You will find a widely repeated claim that pipes are at risk once the air hits 20°F, usually attributed to a university building research programme. We went looking for the study and could not find it stated by any university, by IBHS, or by any federal source, so we do not repeat it as fact. We do report nights below 20°F, because NOAA publishes that count as one of its standard thresholds and it is a good proxy for a hard freeze rather than a light frost. It is a measurement, not a burst point.

Wind matters as much as any number. A cold night with wind driving through the gap where a water line enters a crawl space will freeze a pipe that would have survived a stiller, colder one. This is also why burst calls cluster in the South: a Texas or Georgia house has pipes in unconditioned attics and uninsulated exterior walls, because it was never built for the freeze that arrives once a decade.

How cold your area actually gets

NOAA publishes, for every long-record US station, the average number of nights a year the temperature drops below 20°F and below freezing. Those two numbers describe winter plumbing risk better than any regional generalisation does.

Source: NOAA NCEI U.S. Climate Normals, 1991 to 2020, retrieved 2026-09-09. Each city is matched to the nearest reporting station to its centre, all within about seven miles.

The national spread runs wider still. CENTRAL #2 in AK averages 201 nights below 20°F, roughly 7 months of them. TAMPA INTL AP averages 0.8 nights below freezing and has never recorded enough 20°F nights for NOAA to publish a normal at all. Both places have plumbing. Only one of them has a winter plumbing problem, and the houses in the other one are the ones that split when the rare freeze arrives.

What to do about it

If your ZIP crosses 20°F more than a handful of nights a year, the work is routine and worth doing every autumn: foam sleeves on any pipe in an attic, crawl space or garage, sealed gaps where lines enter the house, hose bibs drained and hoses disconnected, and a plan for which faucet to drip. IBHS advises letting a couple of faucets slowly drain on the lowest floor of the home, and keeping the thermostat at 55°F or higher even when nobody is there. IBHS winter weather ready guide. Fuller prevention guidance is on This Old House, how to prevent frozen pipes.

If it crosses rarely, the risk is concentrated into the one night a decade that catches an unprepared house, and the response is to watch the forecast rather than the calendar. Either way the two pages worth knowing before the cold arrives are when the first freeze lands where you are and what to do the moment a faucet goes quiet. If one has already split, burst pipe repair cost covers what the repair and the water damage behind it tend to run.

Where these numbers come from

The cold-night counts are NOAA normals for the station nearest the ZIP centroid, capped at 75 miles. Two things you will find on competing pages are deliberately absent here. We do not assert that pipes are at risk at 20°F, because we could not find that threshold published by any university, by IBHS, or by any federal source, and we report nights below 20°F only because NOAA publishes that count. And we do not give an hours-to-freeze figure, because no authority publishes one that holds up.

• Freeze dates and cold-night counts: NOAA NCEI U.S. Climate Normals, 1991 to 2020, annual and seasonal by station. Retrieved 2026-09-09. Field definitions are in the by-variable readme.
• ZIP code locations: U.S. Census Bureau 2023 ZIP Code Tabulation Area gazetteer, matched to the nearest station by great-circle distance.
• 2021 International Residential Code, Section P2603.5 (ICC free code viewer) The code trigger for protecting pipes in unheated space, quoted verbatim above.
• IBHS winter weather ready guide The dripping-faucet and thermostat advice quoted on this page.
• This Old House, how to prevent frozen pipes Prevention guidance, the same source used on our frozen pipes page.

The full method, including how we pick a station and what we do when there is not one close enough, is on our methodology page.