At what temperature do pipes freeze? And when to drip your faucets

At what temperature do pipes freeze?

Pipes in unheated spaces start to freeze when it falls to about 20°F outside. That "temperature alert threshold" comes from University of Illinois Building Research Council field tests: uninsulated pipes in an unheated attic began to freeze when the outside temperature fell to 20°F or below, according to the "Freezing and Bursting Pipes" guidance hosted by Multnomah County, Oregon. The City of Phoenix and Texas A&M AgriLife Extension give the same 20°F figure, and Farmers Insurance puts the danger point for indoor pipes at around 20 degrees.

It is a starting point, not a guarantee. The same guidance says freezing can happen above 20°F, especially when wind reaches pipes through cracks in an outside wall or gaps in insulation. Baltimore's public works department warns about stretches below 25°F, and Summit County, Utah says insulated pipes can freeze below 20°F. The document itself says the 20°F threshold is aimed primarily at homes in the South, so in colder regions treat it as a warning sign, not a safe floor.

Do pipes freeze at 32 degrees?

Water freezes at 32°F, Raleigh Water notes, but a 32°F night rarely freezes pipes inside a house. The University of Illinois findings note that an insulated attic may still be 37 or 38°F when it is 32°F outside. Summit County, Utah puts it this way: uninsulated pipes can technically freeze at 32°F but may not freeze hard until it drops below 21°F. Pipes outdoors, in a crawl space or a garage are the exception, and Milwaukee Water Works says the risk builds when it stays below freezing for a long time.

How long does it take for pipes to freeze?

Pipes can freeze in as little as six to eight hours, according to Summit County, Utah, depending on how cold it is, how exposed the pipe is and whether water is moving. That is the only government figure we found; most utilities, extension services and insurers we checked give no time at all, so treat it as a rough guide.

When to drip faucets

Drip a faucet on nights forecast below freezing when pipes run through an outside wall, crawl space, attic, garage or unheated basement. Water utilities that name a trigger use below freezing or 32°F (Portland, Cincinnati, Indianapolis, Louisville, Memphis, Milwaukee), and the City of Lawton, Oklahoma says dripping is most useful when it is well below freezing, often cited around 20°F or lower. The Red Cross says to let cold water drip from faucets served by exposed pipes when it is very cold, because running water through the pipe, even at a trickle, helps prevent freezing.

• Why it works: moving water is less likely to freeze, and if ice does form, which San Antonio Water System says can still happen, an open faucet lets out the pressure that builds between the ice and the closed tap, which is what splits the pipe (University of Illinois findings).
• How much: a stream about the width of a pencil lead (Oklahoma City, Baltimore, Wichita and Cleveland utilities).
• Which faucet: one on an outside wall (Oklahoma City, Louisville), or the one farthest from where water enters the house (Denver Water), from the main shutoff (Austin Water), from the meter (Cleveland Water) or from the front door (Seattle Public Utilities).
• Hot or cold: most utilities say cold. Dallas Water Utilities says hot and cold during a hard freeze, and the University of Illinois findings say each line should contribute to the drip, since both can freeze.
• If the drip stops, leave the faucet open; the pipe may have frozen and still needs the pressure relief.
• Check your utility first. In Houston, the city advises against dripping, and San Antonio and Austin treat it as a last resort.

What 31 city water utilities say about dripping

• Most big-city water utilities never say what temperature to drip at. Of the 31 utilities we checked, 5 give a number (Phoenix 20°F; Baltimore 25°F; Louisville, Memphis and Milwaukee 32°F) and 5 say only "below freezing." The other 21 give no temperature at all.
• The numbers they do give run from 20°F to 32°F. Phoenix says pipes typically begin to freeze at 20°F, Baltimore warns about long stretches below 25°F, and Memphis and Milwaukee use 32°F.
• Houston Public Works advises against dripping, because its system runs on re-pump stations and mass dripping cuts water pressure, KPRC 2 reported. San Antonio has called dripping "not preferred" (December 2020) and Austin calls it a last resort.
• 3 large cities give no drip advice on the winter pipe pages we found: New York, Fort Worth, Charlotte.
• Where they do say how much, it is a pencil lead. Oklahoma City, Baltimore, Wichita and Cleveland all describe a stream about the width of a pencil lead; Wichita puts it at no more than 1/8 inch.

Download the data (CSV)

Checked against each utility's own page or document on October 18, 2026, except Houston (statement reported by KPRC 2) and Memphis (32°F figure reported by WKNO; MLGW's own page asks customers to stop dripping without a number). "None given" means the page gives drip or pipe advice but no temperature. We found no usable official guidance for Los Angeles, San Diego, Jacksonville, Columbus, Kansas City, Atlanta, St. Louis, Las Vegas, Tucson or Albuquerque.

How often it gets cold enough: nights at or below 32°F and 20°F

Minneapolis averages 81.8 nights a year at or below 20°F and Denver 64, in NOAA's 1991 to 2020 climate normals. Houston averages 0.1, so a hard freeze there catches pipes that are rarely tested.

Source: NOAA NCEI U.S. Climate Normals, 1991 to 2020, annual averages for the station shown. Dallas and Fort Worth share the DFW Airport station.

For a ranking that also weighs how old each city's housing is, see our frozen pipe risk rankings. If a pipe has already frozen, how to unfreeze pipes safely covers the steps, and burst pipe repair covers the cost if it split.

Cite this data

Home Repair Dispatch, What city water utilities say about dripping faucets, 2026, https://homerepairdispatch.com/at-what-temperature-do-pipes-freeze/, accessed [date].

The table and CSV are free to use with a link to this page. Please also credit the utilities and NOAA.