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At What Temperature Do Pipes Burst?

Homeowners concerned about freezing pipes might wonder what temperature pipes can freeze and burst, but this is a more difficult questions to answer than many people realize.

While it’s true that water freezes at 32 degrees Fahrenheit, the same does not necessarily hold true for pipes. When the air surrounding pipes dips below this critical threshold, freezing can occur. However, knowing when your pipes would be susceptible to freezing requires additional information than simply just the outdoor air temperature. Understanding regional home building codes, where the pipe is located in your home, and how well the area is sealed off provides the rest of the context that’s needed before you can answer what temperature your pipes will freeze.

Homes in colder northern regions have stricter building codes around home insulation requirements and plumbing layouts, while homes in warmer southern regions have more relaxed building codes around these areas because their added expense isn’t justified based on the climate. In southern states pipes can run along uninsulated exterior walls, while this is a code violation in many northern states. The result is a lower threshold for freeze resistance. Simply put, homes up north can withstand much lower temperatures before homeowners need to worry about freezing.

Remember, your pipes don’t care what the temperature is outside. They only care what the temperature is in the air surrounding them. So, if your pipes are on interior walls or in insulated areas, the air outside needs to be cold enough to cool these areas to 32 degrees. Therefore, plumbers will usually tell you that around here you generally don’t have to worry about pipes freezing unless the outdoor temperature is below zero. However, this is not a hard and fast rule. There are many factors that can influence this number. For instance, older homes may not be as well sealed, meaning that cold air is more prone to entering, raising the “freeze danger” number to more like 10 or 15-degrees Fahrenheit. Additionally, homeowners that turn off their heat when they’re gone risk their pipes freezing because once the heat is turned back on it takes time to re-warm the air in harder to access areas like behind walls.

Interestingly, water freezing in pipes isn’t what typically causes burst pipes. Many homeowners think that water expanding when it freezes is what’s responsible for the burst pipe, resulting in water damage and necessitating a pipe replacement. However, it’s the water pressure building up behind the frozen section that usually causes the pipe to burst.

Prevent pipes freezing and bursting by keeping your heat running continuously during cold weather months and simply turning it down some while you’re gone to be more economical. Sealing up anywhere where cold air can enter, and warm air can escape, will help to keep pipes warmer regardless of where your thermostat is set. Additionally, leaving cabinets open can improve air flow in bathrooms and kitchen to keep pipes warmer. In extremely cold temperatures, leaving water trickling from sink faucets can keep water moving enough to prevent water pressure from building up behind ice and causing broken pipes.

Additional resources:
Call an Emergency Plumber for a Broken Pipe
Do You Need an Emergency Plumber?
What Should You Do When a Pipe Freezes and Bursts?
Does a Burst Pipe Count as an Emergency?
Do Frozen Pipes Burst?
What's Next when a Pipe Bursts in the Winter?