A burst pipe releases roughly 4 to 8 gallons of water per minute, and the average insurance claim for pipe-freeze damage runs north of $10,000. Deciding to let faucet drip to keep pipes from freezing is one of the cheapest insurance policies a homeowner can buy — a slow drip costs pennies per night, while a frozen supply line can flood a finished basement before you wake up. The trick is knowing which faucets to open, how fast the drip needs to be, and when dripping alone will not save you. After decades of winterizing homes from Texas to Minnesota, here is exactly how the technique works and where people get it wrong.
Why a Dripping Faucet Prevents Frozen Pipes
Most people assume the moving water simply refuses to freeze. That is only half the story. Water in a pipe can absolutely freeze while flowing at a trickle if temperatures fall far enough. The real protection comes from pressure relief. When ice forms inside a pipe, the blockage itself rarely splits the copper or PEX. What ruptures the line is the pressure that builds between the ice plug and a closed faucet — trapped water can spike past 2,000 psi as the ice expands, and standard residential pipe fails somewhere between 300 and 1,000 psi depending on material and age.
An open faucet gives that pressure somewhere to go. Even if a partial ice plug forms overnight, the pressure bleeds off through the open tap instead of splitting the pipe wall. The slow flow also pulls slightly warmer water from the main supply through the vulnerable sections, buying you several degrees of margin. Municipal water typically enters the house at 40 to 55°F even in deep winter, which is why moving water freezes far more slowly than water sitting stagnant in an exterior wall.
When to Start Dripping Faucets
The commonly cited threshold is 20°F, and it is a good rule of thumb for most homes. Uninsulated pipes in exterior walls, crawl spaces, garages, and attics start freezing after about six hours of sustained temperatures at or below that mark. Adjust the threshold for your situation:
- Well-insulated newer homes: Start dripping at 15°F or when overnight lows will stay below 20°F for more than a few hours.
- Older homes, pier-and-beam foundations, mobile homes: Start at 25 to 28°F. Skirted crawl spaces lose heat fast and supply lines often run through open air.
- Homes in the South: Start earlier than you think. Southern homes are built for heat shedding, not heat retention, and plumbing frequently runs through unconditioned attics. The 2021 Texas freeze burst pipes in hundreds of thousands of homes at temperatures northern plumbing shrugs off.
- Wind matters: A 10°F night with 25 mph wind drives freezing air into wall cavities and can freeze pipes that survive calm nights at 5°F.
Which Faucets to Drip — and Which Side to Open
You do not need to open every tap in the house. Prioritize by risk. Open the faucet farthest from where the water main enters the house, because dripping that fixture keeps water moving through the longest run of pipe. Then add any faucet served by lines that pass through exterior walls, unheated garages, crawl spaces, or attics. Kitchen sinks on outside walls are the classic freeze point, followed by bathroom sinks above unheated crawl spaces.
Open both the hot and cold sides, or set a single-handle faucet to the middle position so both lines flow. Hot water lines freeze too — in fact they sometimes freeze first, a quirk of the Mpemba effect and the fact that hot lines often sit closer to exterior sheathing. A drip on the cold side only leaves the hot line fully pressurized and unprotected.
Do not forget outdoor spigots. Disconnect hoses, shut interior isolation valves if you have them, and drain the exterior line. A hose left attached traps water in the sillcock and splits it, and you will not discover the damage until the first warm-weather use floods the wall cavity.
How Fast Should the Drip Be?
A drip is not enough in severe cold — you want a thin, steady stream about the width of a pencil lead, roughly 5 to 10 drips per minute at minimum and a continuous 1/16-inch stream when temperatures fall into the single digits. At that rate a faucet moves about 1 to 2 gallons per hour. Run all night, that is 10 to 20 gallons per fixture, which costs most households 5 to 15 cents on the water bill. Compare that with a $500 insurance deductible plus drywall, flooring, and remediation, and the math is not close.
In extreme cold — below 0°F with wind — increase to a stream about the thickness of a cotton string. Check the flow every few hours if you are awake. A drip that slows on its own is an early warning that ice is forming somewhere upstream, and it is your cue to act before the line blocks completely.
What Dripping Faucets Will Not Fix
Dripping is a pressure-relief tactic, not a heating system. It will not protect you in these situations:
- Extended power outages: With the furnace down, interior temperatures can drop below freezing within 24 hours. Dripping delays the freeze but cannot prevent it indefinitely.
- Pipes with no faucet downstream: Washing machine supply lines, ice maker lines, and hydronic heating loops cannot be dripped. They need insulation or heat.
- Septic and drain concerns: If your drain line has a bellied section that holds standing water, a constant trickle can freeze in the drain itself. Rare, but it happens in mobile homes with shallow drain runs.
- Vacant homes: Never rely on dripping in a house nobody is checking. Shut off the main, drain the system, and add RV antifreeze to traps instead.
Pair Dripping With These Freeze-Prevention Steps
Open cabinet doors under sinks on exterior walls so room heat reaches the supply lines — this alone can raise pipe-cavity temperature by 10°F or more. Keep the thermostat at 55°F minimum, even overnight and even when traveling. Seal foundation vents and rim-joist gaps before the cold arrives; a $6 can of spray foam blocks the wind infiltration responsible for most crawl-space freezes.
For chronically vulnerable runs, install foam pipe sleeves ($1 to $3 per 6-foot length) or, better, self-regulating heat cable such as Frost King or EasyHeat models running $30 to $80 for a typical run. Heat cable is the only reliable fix for pipes in unconditioned spaces where dripping and insulation both fall short.
If a Pipe Freezes Anyway
Leave the faucet open. If water stops flowing but nothing has burst, you have an ice plug, and the open tap is still relieving pressure. Locate the frozen section — it is usually where the pipe runs closest to outside air — and warm it with a hair dryer, heat gun on low, or towels soaked in hot water, working from the faucet back toward the blockage. Never use a torch or open flame; contractors see more house fires from pipe-thawing than most homeowners would believe, and overheated water in a blocked line can flash to steam and explode the pipe.
If you find a split or a fitting pushed apart, close the main shutoff immediately and open faucets to drain the system before the thaw turns the split into a flood. Know where your main shutoff is before winter — in a freeze emergency, the five minutes spent hunting for it is the difference between a mop-up and an insurance claim.
The Bottom Line
When a hard freeze is in the forecast, let the faucet farthest from the meter run a pencil-lead stream on both hot and cold sides, open any tap served by exterior-wall plumbing, and swing the cabinet doors open. The water you use in a week of defensive dripping costs less than a fast-food lunch. It is not a substitute for insulation, heat cable, or keeping the furnace running — but as a same-night defense against the pressure spike that actually bursts pipes, it is the most effective free tool you have.
