Frozen pipes: keep the heat at 55°F or higher, and let a faucet drip on hard-freeze nights

Why pipes burst

Water expands as it freezes, and the Red Cross says that expansion can break metal or plastic pipes no matter how strong they are. [S1]

IBHS explains where the break usually happens. Once ice fully blocks a pipe, more freezing pushes up the water pressure in the stretch between the ice and a closed faucet. That trapped section is where the pipe tends to burst, often where little or no ice has formed. On the other side of the plug, water can retreat toward the main, so pressure doesn’t build there. [S2]

The damage adds up fast. Illinois Extension says a crack an eighth of an inch wide can release up to 250 gallons of water a day. IBHS says frozen pipes remain among the most common causes of insurance claims for interior water damage. [S3] [S6]

Which pipes freeze first

The Red Cross lists the usual trouble spots: outdoor hose bibs, swimming pool and sprinkler supply lines, pipes in unheated basements, crawl spaces, attics, garages and kitchen cabinets, and pipes that run along outside walls with little or no insulation. Texas A&M AgriLife adds that a hot water line can freeze too, if water isn’t moving through it. [S1] [S4]

Warm climates aren’t off the hook. IBHS says homes in the South often run plumbing through attics, crawl spaces and outside walls, outside the insulation, and that owners there tend to be less aware of the risk. Northern homes usually keep pipes inside the insulation, but extreme cold and air leaks can still freeze them. Pipe material matters less than you might think: Nebraska Extension says plastic and copper pipes both freeze. [S2] [S3] [S5]

How cold is too cold?

IBHS uses an outdoor “temperature alert threshold” of 20°F for homes in the South and other places where freezes come only once or twice a season. It comes from University of Illinois research in which uninsulated pipes in an unheated attic started to freeze when the outdoor temperature fell to about 20°F. An unheated attic or crawl space usually stays a few degrees warmer than outside, and water “supercools” several degrees below freezing before ice forms. [S2] [S4]

Treat 20°F as an alert, not a guarantee. IBHS says pipes hit by cold air through cracks, or with no insulation at all, can freeze above it, especially on a windy night. Nebraska Extension says that in severe wind chill, even a tiny opening can let in enough cold air to freeze a pipe. [S2] [S5]

The check uses the outdoor forecast low. It can’t see wind, drafts or how well your pipes are protected.

Fall prep, before the first freeze

• Hoses off. Disconnect garden hoses, drain them and store them. [S1] [S5] [S6]
• Outside faucets. Close the inside valve that feeds each outdoor faucet, then open the outside faucet to let it drain. The Red Cross says to leave it open so leftover water has room to expand. Texas A&M suggests an insulated cover over the faucet. IBHS says homes built before 2010 usually don’t have frostproof outdoor faucets. If there’s no inside shutoff, IBHS suggests having a plumber add one. [S1] [S2] [S3] [S4]
• Pool and sprinkler lines. Drain them the way the manufacturer or installer says. The Red Cross says not to put antifreeze in these lines unless the directions call for it, because it’s harmful to people, pets, wildlife and landscaping. [S1] [S4]
• Insulate exposed pipes. Wrap both hot and cold pipes in attics, crawl spaces, garages, under sinks on outside walls and along exterior walls. IBHS says the more insulation the better, and not to leave gaps. Home centers carry sleeves with 1/8 to 5/8 inch of insulation, and specialty dealers sell sleeves up to 2 inches thick. In mild areas, the Red Cross says even ¼ inch of newspaper gives real protection. [S1] [S2] [S3]
• Seal the drafts. Caulk cracks and holes near pipes, including where wiring, dryer vents and pipes pass through outside walls, and seal gaps around windows and doors. [S2] [S3] [S5] [S10]
• Find the main shutoff. IBHS says to know where your home’s main water shutoff is and how to work it. Texas A&M points out why: a frozen pipe may already be cracked, and it will start leaking as soon as it thaws. [S3] [S4]

Heat tape and heat cable

Electric heat tape or heat cable runs along a pipe to keep it from freezing. The Red Cross and Illinois Extension say to choose a UL-listed product. IBHS says to use it with extreme caution, follow the instructions closely, and look for a cable that conforms to UL 2049, the UL outline for residential pipe heating cable. It also suggests one with a built-in thermostat, since a cable without one has to be plugged in each time and can be forgotten. Nebraska Extension adds: use it only where it’s meant to go, indoors or outdoors. [S1] [S2] [S5] [S6] [S8]

The Consumer Product Safety Commission’s heat tape steps date from 1996, but they are still its published guidance:

• Grounded and protected. Plug the 3-prong plug into a 3-prong outlet, on a circuit protected by a GFCI. Our GFCI guide covers the monthly test. [S7]
• On the pipe, not over insulation. Put it directly on the pipe, never on top of the insulation, and don’t wrap it over itself unless the instructions allow it. [S7]
• No foam over it. Don’t cover heat tape with insulation unless the manufacturer says to. If you do, use nonflammable insulation such as fiberglass, not foam or vinyl that could catch fire if the tape fails. [S7]
• Keep the end dry. Keep the end cap sealed and off the ground. Moisture can lead to a fire. [S7]
• Water pipes only. Don’t use water-pipe heat tape on gutters, driveways or fuel lines. [S7]
• Check it each year. Replace it if you see discolored spots (especially at the plug), charring, cuts, breaks in the insulation or bare wire. CPSC also urged replacing uncertified tapes more than 3 years old with tapes certified by UL, CSA or FM. [S7]

In that 1996 release, CPSC estimated that faulty heat tapes caused about 1,500 fires, 10 deaths and 100 injuries a year, and said newer tapes that meet national standards have a much better safety record. [S7]

On a hard-freeze night

• Start a slight drip. Let a faucet fed by exposed pipes drip. IBHS says the drip can be very slight, because its main job is to relieve pressure. Where one faucet has both hot and cold lines, let both drip. Only faucets on pipes at risk need it. [S1] [S2]
• If the drip stops, leave it open. IBHS says a drip that stops may mean ice is blocking the pipe, and the pipe still needs that pressure relief. [S2]
• Open the sink cabinets. Open kitchen and bathroom cabinet doors so room air reaches the pipes. Move cleaners and other chemicals out of children’s reach while the doors are open. [S1] [S5]
• Close the garage. Keep the garage door shut if water lines run through the garage. [S1]
• Hold the heat steady. The Red Cross, Texas A&M and Nebraska Extension say to keep the thermostat at the same setting day and night. The Red Cross admits that may raise the heating bill, but says it can prevent a far costlier repair. [S1] [S4] [S5]
• Heat safely. Ready.gov says never to heat your home with a gas stovetop or oven. [S10]

What’s happening?

Pick the closest match to highlight what the sources say to do next.

Thawing a frozen pipe safely

• Faucet open. Leave the faucet open. As the ice melts, moving water helps melt the rest. [S1] [S4]
• Gentle heat only. Use an electric heating pad wrapped around the pipe, a hair dryer, a portable space heater kept away from anything that can burn, or towels soaked in hot water. Our space heater guide covers plugging one in safely. IBHS suggests starting near the faucet end and working toward the coldest section. [S1] [S2]
• No flame. Never use a blowtorch, a kerosene or propane heater, a charcoal stove or any open flame. Texas A&M says these are a serious fire hazard and give off carbon monoxide. Our CO alarm guide covers where alarms go. [S1] [S4] [S6]
• Mind the water. Keep cords out of water, and don’t use electrical appliances while standing in water. [S2] [S4] [S6]
• Know when to stop. Keep the heat on until full water pressure comes back. Call a licensed plumber if you can’t find the frozen spot, can’t reach it, or can’t thaw it. [S1]

Before the first hard freeze

Run through this once in the fall. Ready.gov also asks for tested smoke and CO alarms with battery backup before winter storms. [S10]

Quick answers