Will pipes freeze tonight?
Enter a ZIP code to see the National Weather Service forecast lows for the next week, and whether any night drops to 32°F or into the 20°F pipe-freeze alert range. Free, no sign-up.
How the checker reads the forecast
| 20°F or colder | Pipe-freeze alert range. In University of Illinois field tests, uninsulated pipes in an unheated attic started to freeze at an outdoor temperature of 20°F or below (ICC summary). |
|---|---|
| 21°F to 32°F | Below freezing. Exposed pipes can still freeze: hose bibs, pool and sprinkler lines, and pipes near drafts in outside walls (ICC, Red Cross). |
| Above 32°F | No freezing night in the forecast. |
The 20°F figure is a worst-case finding for uninsulated attic pipes and is aimed mainly at southern homes, where pipes often run through attics. Every house is different. This is a forecast check, not an inspection.
Before a freezing night
From the American Red Cross: open kitchen and bathroom cabinet doors so warm air reaches the plumbing; let cold water drip from a faucet served by exposed pipes; keep the thermostat at the same temperature day and night; keep garage doors closed if water lines run through the garage; and if you're away, leave the heat on, set no lower than 55°F. If a pipe is frozen and you can't find or reach it, call a licensed plumber.
For plumbing and HVAC shops: send the reminder before the cold night
ForecastBooked checks the NWS forecast for the ZIPs you serve every 3 hours. When the first freeze is in the forecast, a ready-to-edit email, text, Google post and social post for your customers appears on your kit page. Planning the earlier fall message? Use the free tune-up email timer.
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Questions
At what outdoor temperature do pipes freeze?
There is no single number, because it depends on where the pipe runs and how well it is insulated. In University of Illinois Building Research Council field tests, uninsulated pipes in an unheated attic started to freeze when the outdoor temperature fell to 20°F or below. The International Code Council calls 20°F the "temperature alert threshold", mainly for homes in southern states.
Can pipes freeze above 20°F?
Yes. The International Code Council notes that pipes exposed to cold air, especially moving air through cracks in an outside wall, can freeze above 20°F. The American Red Cross lists outdoor hose bibs, swimming pool supply lines and sprinkler lines among the pipes that freeze most often.
Why is 20°F the threshold and not 32°F?
Water in a pipe usually supercools a few degrees below 32°F before ice forms, and an unheated part of a house is usually a few degrees warmer than outside, according to the International Code Council's summary of the University of Illinois research.
How do I keep pipes from freezing?
The American Red Cross recommends opening kitchen and bathroom cabinet doors, letting cold water drip from a faucet served by exposed pipes, keeping the thermostat at the same temperature day and night, and, if you go away, leaving the heat on and set no lower than 55°F.
Where does the forecast come from?
From the National Weather Service forecast for the center of your ZIP code, through the public api.weather.gov service. ForecastBooked is not affiliated with or endorsed by NOAA or the National Weather Service.
See also: Freeze Watch vs Freeze Warning and first freeze dates by city.
Sources
- International Code Council, "Freezing and Bursting Pipes" (summarizing University of Illinois Building Research Council research)
- Gordon, J. R. (1996). An Investigation into Freezing and Bursting Water Pipes in Residential Construction. University of Illinois Building Research Council (IDEALS)
- American Red Cross, "Preventing & Thawing Frozen Pipes"
- National Weather Service API (api.weather.gov)
- National Weather Service, cold weather watches, warnings and advisories
Data: NOAA/NWS. Forecasts come from the National Weather Service API for the center point of each ZIP code. ForecastBooked is not affiliated with or endorsed by NOAA or the National Weather Service.