How to Keep Pipes from Freezing in a Cold Snap

A hard freeze is forecast for the next few nights and the house has pipes running through places that never see heat. Pipes rarely burst at the coldest point of the night; they burst because ice forms, blocks the line, and pressure builds between that plug and a closed faucet. Everything below either keeps the water moving or keeps the pipe warmer than the air around it.

Find which pipes are actually at risk

The vulnerable runs are inside exterior walls, in unheated crawlspaces, basements, garages, and attics, and under sinks on outside walls. Interior pipes in heated space almost never freeze. Walk the house and note which lines cross cold air, because those are the only ones worth protecting tonight.

Let a pencil-thin trickle run overnight

Open the faucet farthest from where water enters the house to a steady stream about the width of a pencil, cold side and hot side both. Moving water is much harder to freeze, and an open faucet relieves the pressure that does the actual damage if a plug forms upstream. Leave it running until temperatures climb back above freezing.

Open cabinet doors under sinks on exterior walls

Room air cannot reach a pipe boxed inside a vanity. Open the cabinet doors so warm air circulates against the supply lines. Move cleaners, drain openers, and anything else hazardous out of reach of children and pets before the doors stay open overnight.

Hold the thermostat at 55F or above

Keep the house at 55F (13C) or warmer, day and night, including while away for the weekend. Setting back at night to save fuel is what leaves a crawlspace line below freezing by 4 a.m. Keep interior doors open so heat reaches rooms on outside walls.

Disconnect garden hoses and close outdoor lines

Pull every hose off every outdoor spigot and drain it. A hose left attached traps water in the spigot where it can freeze and split the pipe inside the wall. If there is an interior shutoff valve for an outdoor line, close it and open the spigot outside to drain what remains.

Insulate exposed pipe and use heat cable correctly

Slip foam pipe sleeves over accessible pipe in cold spaces and seal the seams, paying attention to elbows and the run nearest an exterior wall. For pipe that still freezes every year, use only heat cable that is UL listed for potable water pipe, install it exactly as its instructions specify, and never wrap it over itself or run it under insulation unless the product says to.

When to call a licensed plumber. If the same pipe freezes every winter, the fix is rerouting or insulating the space, not another season of running faucets.