Preventing and Thawing Frozen Pipes

Why pipes burst

Water expands when it freezes, and the pressure it puts on its container can break any pipe, metal or plastic ¹. The split often isn’t at the ice itself: the ice plug traps water between it and a closed faucet, and that’s where pressure builds.

The pipes that freeze first, per the Red Cross ¹:

• Outdoor hose bibs and sprinkler lines.
• Pipes in unheated spaces: basements, crawl spaces, attics, garages.
• Pipes in kitchen and bath cabinets on outside walls.
• Pipes running along exterior walls with little insulation.
• Where the water service enters through the foundation.

What the code does

Wisconsin’s plumbing code builds in freeze protection ²:

• All parts of the water supply must be protected from freezing.
• Water services and private water mains are buried below the predicted frost depth (from the code’s frost-zone map and soil table, next lesson), unless protected some other way.
• Any hose bibb or hydrant through the exterior wall of a heated building must be frost-proof and self-draining: the valve seat sits back inside the warm wall, and when you shut it off, the length of pipe in the cold wall drains out. A hose left connected keeps it from draining, which is how frost-proof bibbs still split.

Before and during the cold

The Red Cross list ¹:

• Before winter: drain sprinkler lines; remove, drain, and store hoses; close the inside valve feeding any old-style bib and leave the outside faucet open so trapped water can expand.
• Insulate hot and cold pipes in unheated areas with foam pipe sleeves, or install UL-listed heat cable following its instructions. A hot pipe freezes just as fast once the water in it sits still.
• In a cold snap: keep the garage door closed if there are pipes in it; open cabinet doors under sinks on outside walls; let the cold water drip from faucets on exposed lines, since moving water is above freezing.
• Keep the thermostat the same day and night during severe cold.
• Away from home, leave the heat on at no lower than 55 °F.

Thawing a frozen pipe

A faucet that only trickles in cold weather is the sign. Find the likely spot, usually where the pipe runs along an exterior wall or comes in through the foundation, then ¹:

1. Open the faucet. As the ice softens, flowing water melts the rest.
2. Warm the pipe with an electric heating pad, a hair dryer, a space heater kept away from anything flammable, or towels soaked in hot water.
3. Keep at it until full pressure returns, and check other faucets for more frozen spots.

Never use a blowtorch, kerosene or propane heater, or any open flame. Water trapped in the pipe can boil and burst it, and flames inside walls start fires and make carbon monoxide ¹. If you can’t find or reach the frozen section, or a pipe has split, shut off the main and call a plumber.

What to take from this

Freezing water expands and splits pipes, starting with hose bibs and lines in garages, crawl spaces, attics, and outside walls. Wisconsin’s code buries services below frost depth and requires frost-proof, self-draining wall bibbs, which only work with the hose off. Insulate cold-space pipes, open cabinets and drip faucets in a cold snap, and keep the heat at 55 °F or more when away. Thaw with the faucet open and gentle heat, never a flame.