Freezing temperatures can cause major problems for plumbing systems. When water freezes, it expands, putting pressure on whatever is containing it. This includes pipes in homes and businesses. If enough pressure builds up, the pipe can burst, leading to costly water damage and repairs. However, it is possible for pipes to freeze without bursting in some cases. There are several factors that determine whether a frozen pipe will burst or not.
What Causes Pipes to Freeze?
Pipes usually freeze when exposed to prolonged freezing temperatures, generally below 32°F/0°C. Certain conditions make freezing more likely:
- Poor insulation – Exposed pipes or those with insufficient insulation are most vulnerable.
- Drafty locations – Pipes located on exterior walls or in crawl spaces are prone to freezing.
- Cracks/gaps – Small openings can let in cold air to freeze pipes.
- Low flow – Stagnant water is more likely to freeze than moving water.
- Low temperature – Extremely cold temps increase chances of freezing.
The most common places for frozen pipes include:
- Attics
- Basements
- Crawl spaces
- Garages
- Kitchen cabinets
- Exterior walls
Any exposed or poorly insulated pipe is at risk when temperatures drop.
Why Do Some Frozen Pipes Burst While Others Don’t?
When water freezes and expands inside a pipe, it puts pressure on the surrounding pipe walls. Whether the pipe bursts or not depends on:
Pipe Material
Some materials are more prone to bursting than others:
- PVC/CPVC – These rigid plastic pipes are highly susceptible to bursting.
- Copper – While strong, copper has some flexibility to withstand expansion.
- PEX – Flexible tubing that expands and contracts with freezing.
- Steel – Almost zero risk of bursting due to the high strength.
In general, rigid pipes like PVC and cast iron are more likely to rupture than flexible tubing like PEX.
Rate of Freezing
If water freezes slowly over an extended period, ice has time to expand gradually. This reduces pressure on the pipe. Rapid freezing causes quick expansion, increasing burst risk. Pipes next to exterior walls freeze faster than those deep within the home’s insulation.
Presence of Trapped Air
When a pipe freezes, any air bubbles present are compressed by expanding ice. This compression absorbs some of the pressure. If no air pockets are present, the pipe has to withstand the full pressure.
Water Pressure
Higher water pressure and volume exert greater force on pipe walls. Household water pressure normally ranges from 30-80 psi. High-end pressures increase the chance of bursting.
Pipe Size
Larger diameter pipes can withstand more internal pressure than small pipes before bursting. 1-inch diameter pipe withstands more pressure than 1/2-inch.
Freeze Location
Where the blockage occurs affects burst potential. Freezing at a joint or bend concentrates pressure in a small area, increasing risk. Freezing in a straight pipe segment distributes pressure.
Signs of Frozen Pipes
It’s important to detect frozen pipes early. Look for these signs:
- Reduced water flow from fixtures.
- No water coming from some fixtures.
- Unusual noises when turning on water, like cracking.
- Higher than normal utility bills if maintaining heat.
- Drop in water pressure.
- Icicles forming on indoor pipes.
Catching a frozen pipe early allows time to safely thaw it before any bursting occurs. Never attempt to thaw a pipe unless you’ve confirmed it’s frozen.
Factors That Prevent Bursting
While frozen pipes are always at risk of bursting, certain factors reduce or prevent rupture:
Gradual Freezing
As noted, slow freezing over hours or days allows ice to expand slowly against pipe walls. The longer the freezing occurs, the more time the pipe has to withstand pressure buildup without bursting.
Plastic Pipes
Modern plastics like PEX and CPVC have some flexibility compared to metals. This allows plastic pipes to expand slightly rather than rupture.
Small Size
Half-inch and 3/4-inch pipes withstand internal pressure better than large pipes due to the smaller volume of expanding ice. Areas most prone to freezing often use small supply lines.
Low Pressure
Household water pressure below 45 psi will typically not burst frozen plastic pipes. Copper and steel pipes can withstand higher pressures when frozen. Turning off the main valve reduces pressure on frozen pipes.
Trapped Air Pockets
Any air bubbles present cushion the pressure of ice expansion. Long horizontal runs have lots of potential for air pockets.
Proper Installation
Professional, leak-free installation leaves no gaps for freezing. Continuous insulation also prevents freezing. Correct pitch allows drainage.
Location
Freezing will occur first at the coldest spot, often at a joint, valve, or bend. Freezing in the middle of a straight pipe run makes bursting less likely.
Thawing Frozen Pipes
If you suspect or confirm a frozen pipe, thaw it safely before bursting occurs:
Locate the Frozen Section
Start by pinpointing the exact frozen location. This may take some time if it’s not obvious. Shut off the main water valve to reduce pressure.
Apply Gentle, Even Heat
Warm the frozen section slowly and evenly with a hair dryer, space heater, or hot water. This allows ice to melt gradually without weakening the pipe. Never use a torch or open flame!
Check Progress Frequently
Monitor the pipe often to avoid overheating any one spot. Melting tends to start from the open end.
Maintain Heat
It may take 30 minutes or more for a thoroughly frozen pipe to thaw. Keep applying a warm airflow until full water pressure is restored.
Test for Leaks
Once thawed, turn the water back on and check for any leaks or drips. Also check for water in the surrounding area that may indicate a burst.
Insulate the Pipe
Add insulation to prevent future freezing. For problem pipes, use heat tape or thermostatically controlled heat cables.
Be Patient
Rushing the thawing process can damage pipes and cause bursting. Allow plenty of time for the ice to fully melt.
Preventing Frozen Pipes
Prevention is the best medicine when it comes to frozen pipes. Take these cold weather precautions:
Insulate Pipes
Ensure exposed water pipes in attics, basements, and crawl spaces are properly insulated. Heat tape or foam tubular insulation helps.
Seal Air Leaks
Caulk and weatherstrip around doors, windows, and openings to prevent drafts near pipes. Insulate exterior walls that contain plumbing.
Disconnect Hoses
Detach and drain any outdoor hoses. Install frost-free hose bibs that shut off water inside to prevent freezing.
Open Cabinets
Keep doors under sinks open to allow indoor air to circulate and warm pipes.
Allow Trickle Flow
Let hot and cold taps drip during extreme cold to keep water moving in pipes. Move between faucets.
Know the Location
Be aware of where water supply lines run through unheated areas. Target these spots for insulation.
Consider Freeze-Resistant Materials
If repeating pipe freezing problems occur, replace pipes with freeze-resistant PEX or CPVC.
Install Heat Tape
Running electric heat tape along pipes provides direct heat when needed. Use UL-approved products.
Seal Windows
Check for any poorly-sealed windows allowing cold outdoor air to flow in on pipes. Caulk and weatherstrip as needed.
Conclusion
Freezing temperatures put plumbing at risk, but pipes can survive if conditions are favorable. Insulated plastic pipes with air pockets in slowly freezing low pressure systems are least likely to burst. Steel and copper pipes can also make it through a freeze. But prompt thawing is a must once discovered. With diligent prevention and early detection, the homeowner can help their plumbing withstand winter’s freezing onslaught.