You should start dripping your faucets when the outside temperature is expected to drop to 28°F (-2°C) or below for four or more consecutive hours. That threshold, not the standard 32°F freezing point, is the trigger because it takes sustained cold to actually freeze water inside insulated walls. If the forecast shows temperatures staying above 28°F, dripping is unnecessary.
Why 28°F, Not 32°F
Water inside your home’s plumbing doesn’t freeze the instant the air outside hits 32°F. Your walls, insulation, and the heat radiating from your house all buffer the pipes. It typically takes temperatures at or below 28°F sustained over at least four hours for pipes to be at real risk. Homes with poor insulation, crawl spaces, or pipes running through unheated areas like garages may be vulnerable sooner, but 28°F for four hours is the widely recommended baseline.
How Dripping Actually Prevents Burst Pipes
A common assumption is that moving water can’t freeze. That’s not quite right. Ice can still form inside a dripping pipe. The real protection comes from pressure relief. When water freezes and expands inside a closed section of pipe, it compresses the water trapped between the ice blockage and the closed faucet. That pressure is what causes the burst. A pipe that’s open on one end, even slightly, cannot pressurize the same way because the expanding ice pushes water out through the open faucet instead of against the pipe walls.
This is also why you shouldn’t panic if the drip stops during a cold snap. A stopped drip likely means ice is forming somewhere in the line. Keep the faucet open anyway. It still provides a pressure release point and will allow water to flow again as the ice thaws.
Which Faucets to Drip
You don’t need to drip every faucet in the house. Prioritize based on two factors: wall location and distance from your main water supply.
- Exterior wall faucets. Any sink, tub, or spigot on an outer wall is most exposed to cold. These are your highest priority, especially in older homes with less insulation.
- The farthest faucet from your water meter. If you drip the faucet that’s the greatest distance from where water enters your home, you pull water through the longest stretch of your plumbing. One well-chosen faucet can protect a large portion of your system.
- Outside spigots. Outdoor faucets should drip around the clock when temperatures will be at or below 28°F for four hours or more. About five drops per minute is sufficient.
If you can identify one interior faucet on an exterior wall that’s also far from the main supply, that single faucet may be the only one you need to run.
How Much Water to Run
You need far less than most people think. A slow, steady trickle is enough, just enough to see consistent movement. For outdoor faucets, roughly five drops per minute does the job. You’re not trying to keep the pipe warm with flowing water. You’re keeping the system open so pressure can’t build. A heavy stream wastes water without adding protection.
Hot Line, Cold Line, or Both
Run the cold water line. Cold water pipes are the most vulnerable because they don’t benefit from the water heater’s warmth. If your hot and cold lines run through different parts of the house and both pass through exposed or exterior areas, dripping both offers extra protection. But if you’re choosing one, cold is the priority.
When Dripping Isn’t Necessary
If your home’s heat is running normally and temperatures aren’t dropping to that 28°F threshold, dripping is overkill. Pipes that are already kept warm by your heating system are unlikely to freeze. A more effective everyday strategy during milder cold snaps is simply opening the cabinet doors under sinks on exterior walls. This lets your home’s warm air circulate around the pipes and is often enough on its own when temperatures hover in the low 30s.
Pipe insulation (foam sleeves or heat tape) on exposed sections in crawl spaces, attics, and garages also reduces the need to drip. Homes with well-insulated plumbing in climate-controlled spaces rarely need to drip faucets at all. The dripping strategy matters most for older homes, homes in regions that don’t typically freeze (where plumbing wasn’t designed for extreme cold), and situations where the power goes out and you lose heat.
What to Do If Pipes Freeze Anyway
If you turn on a faucet and nothing comes out, or the flow slows to nothing during a freeze, a pipe is likely blocked with ice. Keep the faucet open. As the ice begins to melt, water needs somewhere to go, and the open faucet provides that outlet while preventing pressure from building further.
You can apply gentle heat to the section of pipe you suspect is frozen, working from the faucet end back toward the frozen area. A hair dryer, warm towels, or a space heater pointed at the wall all work. Never use an open flame. And before you start, check the area around the pipe for any standing water. If water has already leaked, address that first to avoid slipping or electrical hazards. If you smell something unusual coming from your drains during a freeze, that can indicate a frozen drain line is trapping sewer gases that would normally vent outside.