The full winter storm sequence for a house with a well, a septic tank and no neighbors within shouting distance.
Read the winter storm guide →Every January, plumbing supply houses sell out of couplings in the same forty-eight hours. To prevent frozen pipes you have to understand one thing that is not obvious: the pipe almost never splits where the ice is. It splits somewhere else entirely, and knowing why tells you exactly which faucet to open and which valve to close when the heat is out and the house is dropping a degree an hour.
Ice does not burst the pipe. Pressure does
Water expands roughly nine percent when it freezes, but copper and PEX both have enough give to absorb that locally. What happens instead is that an ice plug forms in the coldest section — usually a run through a crawl space, a rim joist, or an exterior wall on the north side. Water keeps arriving behind that plug from the pressurized side. It has nowhere to go, because the plug blocks one end and a closed faucet blocks the other. Pressure in that trapped segment climbs until the weakest fitting lets go.
That is why the split is often found in a warm part of the basement, ten feet from the actual ice, and why homeowners insist the burst pipe “wasn’t even cold.” It also explains the single most effective thing you can do, which costs nothing.
The drip is a pressure relief valve, not a warming trick
A running faucet does not keep water warm enough to stop freezing. It gives the trapped water an escape path so pressure never builds. The Red Cross puts it plainly: let the cold water drip from the faucet served by exposed pipes. Two practical refinements the advice usually skips.
- Drip the fixture at the far end of the longest, coldest run — usually a bathroom over a crawl space or above an unheated garage. Dripping the kitchen sink protects the kitchen sink.
- If the fixture has separate hot and cold handles, crack both. The hot line runs through the same joist bays and freezes just as readily once the water heater stops firing.
- A steady drip, three or four per second, is enough. A pencil-thick stream is what empties a well pressure tank and makes a pump cycle all night.
- Open the cabinet doors under sinks on exterior walls so room air reaches the trap and supply lines.
Where the cold actually gets in
Ambient air temperature is a poor predictor on its own. The number people use as a working threshold is about 20°F outdoors, sustained for six hours or more, for uninsulated pipes in unheated space. But wind matters more than the reading. A crawl space vent facing into a 25 mph north wind will freeze a line that a still 12°F night leaves alone, because air movement strips heat off the pipe far faster than still air at the same temperature.
Walk the house once in daylight before the cold arrives and note every place a supply line leaves conditioned space: crawl space, garage ceiling, attic runs to a second-floor bath, the hose bibbs, and the well line where it comes through the foundation. Those five spots account for the large majority of failures in a rural house.
Insulation, heat cable, and what each is worth
Foam pipe sleeves are the cheapest useful thing you can buy, and they are also the most misunderstood. A sleeve does not add heat. It slows the rate at which a pipe loses heat, which buys hours, not immunity. On a line with no water moving and no warm air around it, insulation only delays the freeze. It is still worth doing because most cold snaps are measured in hours.
Self-regulating heat cable is the actual solution for a chronic problem run. It draws roughly 3 to 10 watts per foot depending on the model, and it throttles itself down as the pipe warms, so a 30-foot run pulls something like 90 to 300 watts at full cold and much less most of the time. Cable typically runs a few dollars per foot. The catch is obvious and gets people every winter: heat cable is an electrical appliance, and the storm that freezes your pipes is usually the same storm that takes the power out.
| Measure | Rough cost | Needs power | Buys you |
|---|---|---|---|
| Drip a faucet | Pennies | No | Indefinite, if water flows |
| Foam sleeves | $1–3 per ft | No | Several hours’ delay |
| Self-reg heat cable | $3–6 per ft | Yes | Full protection while powered |
| Drain the house | Free | No | Total immunity, no water |
When to stop protecting and start draining
There is a decision point most guides avoid. If the heat is out, the forecast is below freezing for more than about a day, and you have no realistic way to keep the interior above 40°F, dripping will not save you — and if you are on a well, the pump has no power to supply the drip anyway. At that point, drain.
- Shut the main, or the well pressure tank outlet valve if you have one.
- Open every faucet, highest first then lowest, and both hose bibbs. Flush every toilet.
- Kill power to the electric water heater at the breaker, or set a gas unit to pilot, then drain the tank from the bottom valve to a hose.
- Pour a cup of RV antifreeze into each drain trap and the toilet bowls so the traps do not split.
- Leave the faucets open. A closed faucet is half of the pressure trap that breaks pipes.
Draining costs you an evening and a hot shower. A burst line in a crawl space costs a ceiling, a floor, and an insurance claim. Once the heat is genuinely gone for the duration, this is not a close call.
If a pipe is already frozen
Open the faucet that line feeds and leave it open — as the plug melts, flow through the opening tells you it is working and keeps pressure from building. Then apply gentle heat starting at the faucet end and working back toward the cold section, so meltwater has somewhere to go. An electric heating pad wrapped around the pipe, a hair dryer, or a space heater aimed at the joist bay all work. It takes patience, not power.
Safety: Never thaw a pipe with a blowtorch, a kerosene or propane heater aimed into a wall cavity, or a charcoal fire. Open flame in a joist bay full of dust and old insulation is how a frozen pipe becomes a house fire, and unvented combustion in a sealed crawl space is a carbon monoxide problem on top of it.
What we would actually do the night before
Thermostat held at one temperature day and night rather than set back — the setback saves a dollar and costs you the thermal mass in the walls that keeps the crawl space above freezing at 4 a.m. Cabinet doors open on the two exterior-wall sinks. One drip at the far bath. Hoses off the bibbs and the bibbs drained. And the shutoff valve located and tested in advance, because finding it by flashlight in six inches of water is a bad first experience with your own plumbing.
If the house is empty for the season, skip all of it and drain. Red Cross advice for an occupied house away from home is to hold the thermostat no lower than 55°F, and that only works if someone is paying the bill and the power stays on.
Frequently Asked Questions
Should I drip hot or cold water?
Both, if the fixture has separate handles. The cold line is more likely to freeze first, but once a water heater stops firing the hot line is just another cold pipe in the same joist bay.
Does dripping work if I’m on a well and the power is out?
Only until the pressure tank empties, which is usually a few gallons and under an hour of dripping. With no pump, plan on draining the system instead of protecting it.
At what indoor temperature do pipes inside walls start to freeze?
Interior wall cavities usually stay above freezing until the house itself drops into the low 40s and stays there. Pipes in crawl spaces, garages and attics are exposed long before that, which is why they fail first.
Is wrapping pipes in newspaper actually useful?
As a stopgap, yes. The Red Cross notes that even a quarter inch of newspaper provides meaningful protection on a pipe in an unheated space. It is a delay tactic, not a substitute for sleeves or cable.