Water expands when it freezes, no matter the “container” that it’s in. If frozen water expands enough in a pipe, it will burst and result in serious costs in damages. Ice forming in a pipe does not typically cause the break. With complete ice blockage, continued freezing and expansion inside the pipe causes water pressure to increase downstream, leading to pipe failure. Usually the pipe bursts where little or no ice has formed. Pipes are safe when they are within a building’s insulation or there’s insulation on the pipe itself.
In southern states and other areas where freezing weather is the exception, “temperature alert threshold” is 20°F. Field tests of residential water systems subjected to winter temperatures demonstrated that, for un-insulated pipes installed in an unconditioned attic, the onset of freezing occurred when the outside temperature fell to 20°F or below. Freezing incidents can also occur when the temperature remains above 20°F. Pipes exposed to windy, cold air because of cracks in an outside wall or lack of insulation are vulnerable to freezing at temperatures above the threshold.
The best way to keep water in pipes from freezing is to slow or stop this transfer of heat. Place water pipes in only heated spaces and keep them out of attics, crawl spaces and outside walls. A plumber can re route at-risk pipes to protected areas, although this may not be a practical solution. Vulnerable pipes should be fitted with insulation sleeves or wrapping. DO NOT leave gaps that expose the pipe to cold air. Cracks and holes in outside walls should be sealed with caulking. Keep cabinet doors open during cold periods to let the warm air circulate around the pipes. Electric heating tapes and cables are available to run along pipes to keep the water from freezing. Use with extreme caution; follow the manufacturer’s instructions carefully and check to make sure the product conforms to UL 2049.
Letting a faucet drip during extreme cold weather can prevent a pipe from bursting. Opening a faucet will provide relief from the excessive pressure that builds between the faucet and the ice blockage when freezing occurs. If there is no excessive water pressure, there is no burst pipe, even if the water inside the pipe freezes. Pipes vulnerable to freezing should be left with the water flowing. Even the slowest drip at normal pressure will provide pressure relief when needed. Where both hot and cold lines serve a spigot, make sure each one contributes to the drip, since both are subjected to freezing. If the dripping stops, leave the faucet(s) open, since a pipe may have frozen and will still need pressure relief.
If you open a faucet and no water comes out, don’t take any chances. Call a plumber. If a water pipe bursts, turn off the water at the main shut-off valve. Leave the faucet(s) open until repairs are completed. Don’t try to thaw a frozen pipe with an open flame; as this will damage the pipe and may even start a fire. You might be able to thaw a pipe with a hand-held hair dryer. Slowly apply heat, starting close to the faucet end of the pipe, with the faucet open. Work toward the coldest section. Don’t use electrical appliances while standing in water; you could get electrocuted.