Water freezes when the temperature falls below freezing, like making ice cubes in your freezer. When water freezes it expands,and in a pipe it may expand enough to burst the pipe depending on how much pressure builds up in the pipe. If a plumbing pipe bursts, the water escapes and goes in many directions and may cause serious damage … and the worst case is when the pipe bursts inside the walls, where you can hear it but can't see it. That's when you need to shut your water off as quickly as possible (read Learning to Shut Your Water Off).
Houses in northern climates are built to withstand freezing temperatures. Pipes have insulation between the exterior wall and the water pipes, protecting them from freezing weather. The biggest risk is where there are holes or cracks that allow cold air to enter the home and cause the temperature surrounding the pipe to drop. Water pipes in warmer climates are more likely to lack adequate insulation to protect them from freezing temperatures as they occur infrequently and homeowners aren't as aware of the problems.
What Causes a Pipe to Burst
Let's explore more familiar instances of freezing water. Ice cube trays allow the water to expand up as the water freezes. If you leave a full bottle of water/soda in the car during the winter or put it in the freezer to cool quickly and forget it, the bottle may burst. As the water in the bottle freezes and expands, the air compresses and the pressure builds until it bursts to relieve the pressure.
In the same way ice forms in the pipe, typically creating an ice blockage that initially doesn't cause the pipe to burst. It's not until continued freezing occurs and more water freezes between the ice blockage and the closed faucet, that the pressure builds until the pipe bursts. On the other side of the ice blockage, the water is able to back up towards the source of the water.
Uninsulated pipes in unconditioned spaces will begin to freeze when the outside temperature reaches 20 degrees Fahrenheit or lower. Most problems occur with temperatures in their teens although high winds can force cold air through cracks in the outside wall and freezing may occur above 20 degrees.
Which Pipes are Most Likely to Freeze
You first want to understand which pipes are most vulnerable to freezing, as these are the ones you want to focus on as you take steps to avoid future freezing risk. Pipes located in the following areas are most vulnerable:
- Pipes that carry water outside the house like exterior faucets.
- Water pipes on the exterior walls that aren't insulated, don't have enough insulation or don't have the insulation between the pipes and the exterior wall.
- Pipes carrying water in unconditioned places like the garage, basement or attic.
- Water pipes under kitchen and bathroom sinks on exterior walls are vulnerable to freezing when room temperatures are set low, i.e. 50 degrees when you leave on vacation. Cabinets doors prevent warmed air from mixing with the colder air coming through exterior walls.
Preventing Frozen Pipes
Ideally most water pipes are placed in heated spaces, running along interior walls. This is good home design but sometimes gets lost while satisfying more functional and aesthetic requirements. Here are some of your choices for dealing with pipes that are vulnerable to freezing.
- When accessible, consider having a plumber re-route the pipes through an inside wide … so maybe that bathroom remodel you've been thinking about will happen sooner?
- If pipes can't be moved, you can wrap the pipes with insulation sleeves, and fill any nearby gaps and cracks responsible for exposing the pipes to cold air.
- Heating cables aren't ideal but if you decide to use them, make sure the product you buy is UL rated for the job and follow the manufacturer's directions to avoid the risk of a fire. Heat tape with a built-in thermostat to control the heat is safer than one you have to remember to plug in each time it's needed.
- Letting the water run at a slow flow won't prevent freezing but should reduce the pressure build-up that causes pipes to burst … and leave the faucet open even if drip stops, until temperatures are above freezing. Remember that a dripping faucet does waste water so only do this for faucets that are likely to freeze.
- Don't set thermostats too low when going away for an extended period. Leave kitchen and bathroom cabinet doors open so the pipes under sinks are as warm as the room.
- Add insulation to an exterior wall where there are water pipes. My handyman business has worked with several customers to do this where a master bedroom/bathroom was added over a garage and no insulation was put in the walls.
- The best safeguard is to drain the system if the risk is high, i.e. the way summer homes are closed for the winter.
When the Pipe Freezes
When you think a pipe has frozen, i.e. when you open a faucet and no water comes out, it's time to call a plumber. Turn off the water at the main shut-off valve (read Learning to Shut Your Water Off) until needed repairs are completed. You can try thawing the pipe with a hand-held hair dryer starting close to the faucet. If there is any standing water, do not use any type of electrical appliance. Don't try using any type of open flame as this could start a fire.