How to winterize pipes: the checklist, and when heat cable makes sense

Where pipes freeze, and at what temperature

Water pipes do not freeze because the house is cold. They freeze because one section of pipe sits in air that is much colder than the rest, usually with a draft moving across it. The suspects are the same in every house: outside hose bibs, supply lines in a vented crawl space, pipes in an unheated garage or along a garage wall, lines inside exterior walls behind kitchen and bathroom cabinets, anything in an attic, and plumbing in an unheated addition, porch or bonus room over a garage.

The number to watch is 20°F. The Insurance Institute for Business & Home Safety puts the point where unprotected pipes in unheated spaces begin to freeze at about 20°F outdoors, and the first night the forecast crosses it is when the calls started for us. In cold climates the risk is a long stretch of single digits; in the South it is the one hard freeze a decade that finds every uninsulated pipe at once, because nobody there has ever had to think about it.

Insulation slows heat loss; it does not add heat. A sleeved pipe in a 10°F crawl space with a draft on it will still freeze, just later. That is why the checklist starts with keeping cold air off the pipes and ends with heat cable only where nothing else works.

Tools and materials

• Foam pipe sleeves sized to the pipe's outside diameter (1/2 in. copper is 5/8 in. OD, 3/4 in. is 7/8 in. OD; PEX and CPVC are labeled by nominal size on the sleeve bag), with the seams taped
• Spray foam or caulk for gaps where pipes pass through the rim joist, sill, walls and floors; foam blocks or vent covers for crawl space vents
• Insulated hose bib covers
• A flashlight, gloves, a utility knife and tape
• If a run needs it: UL- or CSA-listed self-regulating pipe heat cable in the right length, a GFCI-protected outlet within reach of its plug, and fiberglass pipe wrap if the cable's instructions allow insulation over it
• For a vacant house: RV (propylene glycol) antifreeze for traps and toilet bowls, never automotive antifreeze
• A thermometer or a leak sensor that reports temperature for the coldest spot

Heat cable: when it makes sense and how to do it safely

What it is. Pipe heat cable (heat tape, heat trace) is an electric heater that runs along the pipe under insulation. Self-regulating cable changes its own output with temperature, puts out more heat where the pipe is coldest, can be cut to length from a reel, and can usually be overlapped and run under insulation; it is the kind we would use on anything we cared about. Constant-wattage cable comes in fixed lengths with a plug and a built-in thermostat, costs less, and has stricter rules about overlapping and insulating because it keeps heating regardless.

When it is the right answer. A run that stays in freezing air after you have sealed the drafts and sleeved the pipe, and that you cannot move inside the heated envelope: crawl space supply lines with no insulated floor above, well house and outbuilding lines, pipes on the cold side of a garage, mobile home risers, and the occasional sump discharge or condensate line that freezes solid. It is the wrong answer for a pipe in a kitchen cabinet; open the door and fix the draft.

The safety rules, from the CPSC and the cable makers. The Consumer Product Safety Commission has estimated that about 1,500 fires, 10 deaths and 100 injuries a year result from faulty heat tapes, most of them old, uncertified or misapplied. Its guidelines, which match what every manufacturer's instruction sheet says:

• Buy only cable certified by UL, CSA or FM, and use it only on the pipe material the instructions list; some cables are for metal pipe only, and plastic pipe needs a cable rated for it.
• Plug it into a GFCI-protected outlet, with a grounded three-prong plug, and never an extension cord.
• Apply the cable directly to the pipe, not over insulation, following the maker's spacing or spiral pitch; do not wrap it over itself unless the instructions specifically allow it (self-regulating usually does, constant-wattage usually does not).
• Insulate over it only if the instructions say so, and then with fiberglass pipe wrap, not foam or vinyl, unless the cable is listed for use under foam.
• If the cable has a thermostat, mount it where the instructions say: in contact with the pipe, under the insulation, at the coldest point.
• Keep the end seal and the plug dry and off the ground. Do not run the cable through walls, floors or ceilings, and keep it off valves and unions unless the instructions show how.
• Inspect it every fall: discoloration at the plug, charring, cracked or cut jacket, bare wire. The CPSC recommends replacing uncertified tape more than three years old; we would replace any cable that shows damage regardless of age.
• Test it before the freeze: a self-regulating cable warms slowly to the touch when plugged in on a cold day; a thermostatic cable will not turn on until the pipe is near 40°F, so test it per the instructions rather than assuming.

Heat cable protects the length of pipe it touches. A cable that ends a foot short of the elbow at the wall protects everything except the elbow, which is where the split happens.

The cold-snap routine

The night the forecast crosses 20°F, or any night below freezing in a house that has never been winterized:

• Open the cabinet doors under every sink on an exterior wall, kitchen and bathrooms, so room air reaches the pipes. Move the cleaners out of reach of children first.
• Let a faucet drip. A trickle the width of a pencil lead from the faucet farthest from where the water enters the house, and from any faucet fed by a pipe in an exterior wall; open the hot side a little too. Moving water freezes later, and an open faucet relieves the pressure that actually splits a pipe when ice forms behind a closed valve.
• Keep the garage door closed if there are water lines in or along the garage, and the door between the garage and the house closed too.
• Keep the thermostat at one setting day and night, and never below 55°F when you are away, which is the Red Cross guidance. A nightly setback to 60°F in a drafty house is enough to freeze a pipe in an exterior wall that was fine at 68°F.
• Leave interior doors open so heat reaches the rooms over the garage and at the ends of the house.
• Check the coldest pipe you flagged in the fall, by hand or by the sensor, before bed.

Leaving for the winter

For a house that will sit empty in freezing weather for more than a few days:

1. Close the main shutoff and open every faucet, hot and cold, highest to lowest, until they stop. Open the outside bibs and the drain on the main if there is one.
2. Turn off the water heater (breaker for electric, control to OFF or VACATION for gas) before you drain the house, so an electric element is never energized above the water line. If the house will be unheated, drain the heater through its drain valve to a floor drain.
3. Flush each toilet with the water off and hold the handle to empty the tank, sponge the last of the bowl out, and pour RV antifreeze into the bowl and into every sink, tub and shower trap. Never automotive antifreeze.
4. Drain or bypass the water softener, the icemaker line and any filter housings per their instructions; they hold water in places that split.
5. Leave the heat on at 55°F if the house is not fully drained. If it is drained and the heat is off, leave cabinet doors open anyway so the empty pipes are not stressed by trapped water at low points.
6. Have someone walk through weekly, or put a temperature-reporting sensor in the coldest room and the crawl space so your phone knows before the pipes do.

Freeze alerts: let a sensor stand watch

The sensors we already recommend for leaks earn a second job in winter. A leak sensor that reports temperature, placed at the coldest pipe you found in the fall, warns you when the crawl space or the garage wall drops toward freezing, hours before a pipe does, and the same device tells you the moment the pipe lets go. Set the low-temperature alert in the high 30s. Two that do it well, and where each belongs:

Crawl spaces and detached buildings are often beyond Wi-Fi; a long-range LoRa system reaches them, and the leak detector roundup covers the options. Our sensor placement guide has the map for the rest of the house.

When to call a pro

Call a plumber to reroute a line that freezes every winter out of the exterior wall or crawl space, to replace a standard hose bib with a frost-free sillcock, to install heat cable on a long or hard-to-reach run and the GFCI circuit it needs, to thaw a pipe inside a wall or ceiling, or to winterize a vacant house if you are not sure every low point has drained. Call a landscaper or irrigation company for the blowout if you do not own a compressor that can deliver the volume. If a pipe has burst, the first call after the main is off is the emergency page, which reaches plumbers and restoration contractors through HelpMeNow.com; the form below is for the planning jobs.