Guide

How to Keep Pipes From Freezing

How do I stop my pipes freezing tonight?

Start with the pipes outside — drain and disconnect hoses, cover outdoor taps. Then open cupboard doors under sinks on exterior walls, keep the heating on overnight instead of setting it back, and run a pencil-thick trickle from the furthest tap once the overnight low approaches 20 °F. Insulation is a summer job.

Tonight, in order of how much it helps

If the forecast has turned and you have an hour, do these in this order. The list is ordered by protection per minute spent, not by category.

Disconnect the hoses. A hose left attached holds water against the tap and stops the tap draining. This is the single most common cause of a burst outdoor tap, and it takes thirty seconds to fix.
Drain and isolate anything outdoors. Outdoor taps, irrigation, pool lines. If there is an indoor shut-off for an outdoor tap, close it and then open the outdoor tap to let the section between them empty.
Cover the outdoor taps. A foam tap cover costs very little. A towel and a plastic bag, tied on, is most of the benefit.
Open the cupboards. Under sinks on exterior walls, open the doors so room air reaches the pipes. On a kitchen sink against an outside wall this is worth several degrees at the pipe.
Leave the heating on overnight. Do not set it back on a night below about 20 °F. Everything protecting the pipes in your walls and voids is heat leaking out of the heated rooms.
Set a trickle running. Once the low is near or below 20 °F, a pencil-thick trickle on the furthest tap. Moving water freezes more slowly, and an open tap gives pressure an escape route if an ice plug forms anyway — which is the part that prevents a burst.
Find the stop tap. Before you need it, in the dark, with water coming through a ceiling. Make sure it turns.

The jobs that belong to summer

Everything above is a response. These are the fixes that mean you stop having to respond, and none of them can be done usefully on the night:

Insulate the pipes in unheated spaces. Foam sleeve on every run in the crawl space, garage, attic and any unheated basement. Pay attention to the joints and bends, which is where sleeve kits are usually left short.
Seal the air leaks near pipes. A gap in the siding or a missing plate around a pipe penetration lets outside air blow directly onto the pipe. Sealing the leak is often worth more than the insulation.
Close the crawl space vents for winter, and check nothing has pulled the insulation down off the underside of the floor.
Fit a frost-proof outdoor tap if you keep losing the same one. The valve sits inside the heated envelope and the pipe drains itself every time you close it.
Fit a heating cable to the run that always freezes. If it has frozen twice, it will freeze again.

What does not help as much as people think

Turning the heating up during the day. The pipes freeze overnight. A warm afternoon does not carry through to 4 am; a thermostat left at its evening setting does.
Opening every tap. One trickle on the right tap does the job. Six taps running is six times the water for no extra protection.
Insulating a pipe and nothing else. If the space around the pipe is at 10 °F for twelve hours, insulation is delaying the inevitable rather than preventing it.
A space heater left in a crawl space unattended. The fire risk is real and the coverage is poor. A heating cable on the pipe is the safer version of the same idea.

The exception that causes most of the serious damage

An empty house in a cold snap. No one is running taps, no one notices the heating has failed, and no one is home when the thaw arrives. If you are away in winter, hold the thermostat at 55 °F (13 °C) or above, shut off the water supply if you can drain the system, and ask someone to look in.

If you are leaving the house for the winter

The full version, for a property standing empty for weeks:

Close the main stop tap.
Open every tap, upstairs first, and let the system drain down.
Drain the water heater if the manufacturer's instructions allow it.
Leave the heating running at 55 °F (13 °C) anyway, for the parts that will not drain and for the building itself.
Have somebody check the property, especially after a cold night.

Draining is what makes the difference. A pipe with no water in it cannot burst, no matter how cold the night gets.

How cold before you bother

There is a threshold below which none of this is worth doing, and it is higher than people expect:

Low above 32 °F (0 °C): nothing to do.
Low of 32 to 25 °F (0 to −4 °C): hoses off, outdoor taps drained and covered.
Low of 25 to 20 °F (−4 to −6 °C): add the cupboard doors and the overnight heating.
Low at or below 20 °F (−6 °C): add the trickle, and check the stop tap turns.
Low below 15 °F (−9 °C), or several such nights running: all of the above, and expect the risk to compound each night rather than reset.

The reason the threshold sits near 20 °F rather than freezing point is covered in what temperature pipes freeze at — briefly, a heated house keeps the spaces its pipes run through above the outdoor air temperature, so the outdoor number has to overshoot before the water inside turns to ice.

Common questions

Should I leave the heating on all night, or is a setback fine?

On a night at or below about 20 °F, leave it on. A setback saves a small amount of money and costs you the margin that keeps the spaces around your pipes above freezing. Through the rest of winter a setback is fine — this is an exception for the coldest nights of the year, not a change of habit.

Which tap should I leave dripping?

The one furthest from where the water enters the house, so the trickle pulls water through the longest run of pipe. If the vulnerable run serves a particular sink, use that one instead. A trickle roughly the thickness of a pencil lead is enough; a fast-running tap wastes water without adding protection.

Does insulating pipes actually stop them freezing?

Insulation slows heat loss, it does not add heat. It buys hours, which is usually the difference on a normal cold night, but a long enough cold snap will freeze an insulated pipe too. Insulation on a pipe in an unheated space works best combined with something that keeps the space itself above freezing.

What about heat tape or a trace cable?

An electric heating cable is the one measure that adds heat rather than conserving it, so it is the right answer for a run that freezes every year. Buy one rated for the pipe material, fit it to the manufacturer's instructions, and do not spiral it under insulation unless the instructions say to.

My pipe is already frozen — what now?

Open the tap that pipe feeds, so meltwater and pressure have somewhere to go, then warm the pipe from the tap end back towards the blockage with a hairdryer, a heat gun on low, or towels soaked in hot water. Never use an open flame. If you cannot reach the frozen section, or you see a bulge or a split, close the stop tap and call a plumber.

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