At What Temperature Do Pipes Freeze?
Pipes generally start to be at risk when the outdoor temperature holds at or below about 20F for several hours. The air temperature alone is not the whole answer, because duration, wind and where the pipe runs matter as much as the number.
What to do right now
Do these first. None of them need tools or plumbing knowledge, and they limit what this ends up costing you.
- Watch the forecast for duration, not just the lowA single hour at 18F is far less dangerous than twelve hours at 22F. Sustained cold is what freezes pipes.
- Think about where the pipe is, not where the thermostat isA crawlspace or a garage can sit ten to fifteen degrees below the living space. The number that matters is the temperature at the pipe.
Does this need a plumber tonight?
- A pipe that has already frozen
- No water during a cold snap
- Cold weather with no symptoms
- Preventative work before a forecast freeze
Why 20F is the number people quote
Because it is the point at which an uninsulated pipe in an unheated space, exposed to outside air, will typically reach freezing itself after several hours. Water freezes at 32F, but pipes rarely sit at outdoor air temperature.
A pipe inside a heated house is protected by the building. A pipe in a vented crawlspace is not, and it will approach outdoor temperature within hours. That gap is why the threshold is stated below freezing rather than at it.
Wind matters because it strips away the thin layer of warmer air around a pipe and around the building. A windy 25F night can do more damage than a still 18F one.
What that means here
In Ogden, overnight lows sit below 20F regularly through winter. In the Ogden Valley they do so for extended stretches. This is not a rare risk locally, it is a normal seasonal condition.
The practical consequence is that prevention should be routine here rather than reactive. Disconnecting hoses in October and closing crawlspace vents is cheap seasonal maintenance in this climate rather than an unusual precaution.
It also explains why frozen pipe calls in our area cluster on the second and third night of a cold snap rather than the first. It takes sustained cold to bring a pipe down to freezing.
Questions people ask about this
Will my pipes freeze at 30F?
Pipes inside a heated house almost certainly not. A pipe in an unheated crawlspace exposed to wind, over a long night, possibly. Where the pipe runs matters more than the headline temperature.
How long does it take a pipe to freeze?
Typically several hours of sustained cold rather than minutes. That is why the second and third nights of a cold snap produce more failures than the first.
Does it matter if the pipe is full or empty?
Enormously. A drained pipe cannot freeze in any damaging way, which is why draining outside lines and unoccupied properties is such effective prevention.
If that is not quite what you have
Not sure how urgent this is?
Describe what you can see and hear. We will tell you whether it needs someone tonight, and what to do in the meantime either way.
Or send it over
Four things and a photo.