How to Keep Pipes From Freezing (and at What Temperature)

At what temperature do pipes freeze?

Water turns to ice at 32°F, but the air outside has to be colder than that before the water inside a sheltered pipe gets there. The figure to plan around is 20°F: Texas A&M AgriLife Extension writes that water pipes have the potential to freeze and burst when the outside temperature reaches 20°F or below. Treat a forecast of 20°F as the night to act.

The same source lists the pipes that freeze first:

• Outdoor faucets (hose bibs).
• Swimming pool and lawn sprinkler supply lines.
• Pipes in basements, crawl spaces, attics and garages.
• Pipes that run against outside walls with little or no insulation.

A hot water line can freeze just as a cold one can, once the water in it has stood long enough to go cold. It is a bigger worry in the South than many people expect, because pipes there often run through attics and crawl spaces with little insulation.

Eight steps to keep pipes from freezing

The first four are jobs for the fall, and the last four are for the cold night itself. They come from Texas A&M AgriLife Extension and University of Illinois Extension.

1. Insulate the exposed pipes. Fit foam tubes (pipe sleeves) on the pipes near outside walls, in the crawl space, the attic and the garage. The tables below give the tubes to buy.
2. Seal the air leaks. Close the gaps that let cold air blow onto the pipes. For the doors and windows, see the weatherstripping calculator: one 36 × 80 in door takes 16.3 ft.
3. Disconnect and drain outside. Take off the garden hoses, close the inside valve that feeds each outdoor faucet if there is one, drain the line and fit an insulated cover.
4. Think about heat tape. On a pipe that has frozen before, a heat tape or heat cable with a UL listing, fitted by the maker’s instructions, adds warmth that foam alone cannot.
5. Keep the heat steady. Hold the thermostat at the same setting day and night in a cold snap, and never below 55°F, including when you are away.
6. Open the cabinet doors. Let the warm air of the room reach the pipes under the kitchen and bathroom sinks.
7. Let a faucet trickle. Run a thin stream of hot and cold water overnight from a faucet on an outside wall.
8. Keep the garage door shut if water lines run through the garage.

Going away in winter? Leave the heat on at 55°F or more, and have someone look in each day to check it is still running, or shut off and drain the water system.

How many foam tubes to buy

Each pipe size needs its own tube, so measure the 1/2 in and the 3/4 in pipe separately. Elbows and tees use extra, about 6 in each, and 10% is added for cutting. The counts here are for tubes of 6 ft; check the length printed on the package, because 50 ft of pipe takes 12 tubes of 6 ft but 9 tubes of 8 ft.

Pages for one length of pipe, with other tube lengths and fitting counts: 10 ft, 20 ft, 30 ft, 50 ft, 75 ft and 100 ft.

Tubes for common trouble spots

These jobs are examples to show the method, so measure your own pipes before you buy:

Worked example

A house has 20 ft of 1/2 in pipe with 4 fittings and 30 ft of 3/4 in pipe with 6 fittings in the crawl space. With 6 in for each fitting and 10% extra, the 1/2 in pipe comes to 24.2 ft, which is 5 tubes of 6 ft. The 3/4 in pipe comes to 36.3 ft, which is 7 tubes. That is 12 tubes in all. The short pipes under a sink on an outside wall (6 ft with 4 fittings) take 2 tubes more.

If a pipe has already frozen

A faucet that gives only a trickle, or nothing, on a freezing morning can mean ice in the line. Texas A&M AgriLife Extension gives these steps:

1. Keep the faucet open. As the ice melts, running water helps to melt the rest.
2. Find the main water valve before you start. The pipe may have split, and it will leak once it thaws.
3. Warm the frozen stretch with a heating pad, a hair dryer, a portable space heater or towels soaked in hot water. Keep electrical cords away from water.
4. Never use a blowtorch, a kerosene or propane heater, a charcoal stove or any open flame. They can start a fire and give off carbon monoxide.
5. Keep going until full water pressure returns, then check the other faucets, since one frozen pipe often means more.
6. Call a licensed plumber if you cannot find the frozen part, cannot reach it, or cannot thaw it.

The damage is the reason to hurry: University of Illinois Extension notes that a crack one eighth of an inch long can release up to 250 gallons of water a day. Take care around standing water and electricity, and call your insurance agent if a pipe has burst.

What else to get ready

A long power outage in a hard freeze stops the furnace, so pipes are at more risk then: the generator size calculator adds up what you need to keep the heat running. Sealing two doors and ten windows takes about 223 ft of weatherstripping, and the attic insulation calculator covers the attic floor. For the rest of the season, follow the winter home prep checklist.

The tube counts are estimates from the lengths you enter. The temperatures are general guidance from the two extension services named above, not a guarantee for your house.

Frequently asked questions