Short answer: yes, when the forecast drops below about −25°C, on the taps that actually need it. But dripping is the least important of the things worth doing, and a lot of people do it instead of the measures that matter rather than alongside them.
It also isn't free. A tap running for four days in a cold snap uses a meaningful amount of metered water, and if it's the hot tap you're heating that water too. So it's worth knowing which taps, how much, and when it's genuinely doing something — because on most Calgary homes, most winters, it isn't. If a pipe has already stopped running, skip ahead to frozen pipe repair — that's a different problem with a clock on it.
Why a dripping tap helps at all
Two reasons, and the second matters more than the first.
Moving water freezes more slowly. Not "never freezes" — a thin trickle in a −30°C rim joist will still ice up eventually. It buys time, not immunity.
It relieves pressure. This is the real mechanism, and it's the one almost nobody explains.
When water freezes it expands by roughly nine percent. But a pipe rarely bursts at the ice itself. What happens is an ice plug forms somewhere, and the water still liquid between that plug and your closed tap has nowhere to go as the plug keeps growing. Pressure climbs in that trapped section until the pipe splits — often at a spot well away from the actual ice, sometimes in a completely different room.
An open tap gives that trapped water somewhere to go. The pipe can still freeze solid, but it's far less likely to split, which is the difference between a bad morning and a flooded basement.
That's why the advice is "leave it open," not "leave it dripping." The opening matters more than the flow.
Which taps, and how much
Not all of them. Dripping every tap in the house is waste with no added protection.
Open the taps on pipes with cold exposure — those are the ones at risk:
- Anything on an exterior wall, especially a kitchen sink under a window
- The fixture furthest from your mechanical room, which sits at the end of the longest run
- Anything above an unheated space — a cantilevered bump-out, a garage, a crawlspace
- Bathrooms in a bonus room over the garage
Open both hot and cold on those fixtures. Hot lines freeze too, and people are consistently surprised by that. Hot water actually holds less dissolved air and, in some conditions, can begin freezing sooner than cold — the hot line is not the safe one.
On flow: aim for a thin continuous stream, roughly the thickness of a pencil lead — not a slow drip. A drip that falls once a second isn't enough movement to matter, and a drip can stop entirely if the line ices partway. A visible steady trickle is doing the job.
If your kitchen and bathroom share a mixing tap, set it to lukewarm so both lines are moving.
The things that matter more
If you only do a few things before a deep freeze, do these instead — and add the dripping on top.
Open the cabinet doors under sinks on exterior walls. Cheap, instant, and it does more than the tap. The pipe under your kitchen sink is often separated from outside air by nothing but the cabinet back and the wall sheathing. A closed cabinet is an insulated box keeping your house heat out of the space where the pipe lives. Open the doors and let the room reach it.
Keep the heat on, everywhere. Not just the rooms you use. A closed door on an unused bedroom on the north side, with the vent shut to save money, is exactly how the pipes in that wall freeze. If you're going away, don't drop the thermostat below about 15°C, whatever the savings look like.
Disconnect the garden hose. Every autumn, and every autumn people forget. A hose left connected traps water in the bib and the short run behind it, and that section is outside the building envelope. It's the single most common freeze we attend, and it's completely preventable in about a minute.
Know where your main shutoff is, and that it turns. If a pipe does let go, the time between the split and the water stopping decides how expensive the day is. Find the valve now, and turn it a quarter turn to confirm it isn't seized — plenty of them are, and finding out during a flood is the worst way to learn.
How long does it actually take to freeze?
The question underneath the dripping question. There's no single number, because it depends entirely on exposure, not just temperature.
An exposed pipe in an unheated space — a garage, a crawlspace, an uninsulated bump-out — can freeze within a few hours once it's below about −18°C, and faster with wind moving across it. Wind is the underrated variable. A rim joist with a gap in the sheathing behaves very differently in still air than in a north wind.
A well-insulated interior pipe in a heated home might not freeze at all, through the worst night of the year.
Which is why "how cold does it have to get" is the wrong question. The right one is "where in my house does outside air reach a water line" — and that's what actually decides it. Our frozen pipe repair page has the specific spots we find over and over in Calgary homes, and it is a short list that repeats itself across thousands of houses.
The Calgary versions of this problem
Chinooks make it worse, not better. A freeze-thaw-freeze cycle is harder on plumbing than a steady cold spell. Things shift, a pipe that thawed unnoticed on Tuesday is refrozen by Thursday, and a split that opened during the thaw doesn't announce itself until it's under pressure again.
Weekends in the mountains. A house that would be perfectly fine occupied gets its thermostat dropped, the doors closed, and no one home to notice the kitchen tap has stopped running. Most burst pipes we attend in vacant houses ran for hours before anyone knew. If you're away and it's forecast cold, leave the heat at 15°C or above and have someone look in.
Cantilevered bump-outs. Very common in Calgary builds and a genuine weak point — the floor of that bay is exposed to outside air on the underside, and builders routinely ran supply lines through it with thin insulation. If you have a bump-out with plumbing in it, that's your most likely freeze point in the house.
Newer homes are not exempt. Tighter building envelopes are better in general, but a poorly sealed rim joist or an unsealed hole where a service enters is a cold-air path regardless of the year on the permit. We attend freezes in ten-year-old houses most winters.
Does PEX change any of this?
Somewhat. PEX has more give than copper and can sometimes expand with an ice plug and survive where copper splits. That makes it more forgiving — not freeze-proof.
The fittings are still rigid, and it will still burst if the pressure has nowhere to go. It also freezes at the same temperature as everything else; there is no material that stops water turning to ice. Treat a PEX house exactly as you'd treat a copper one.
When dripping is not the answer
If a tap that was running has slowed to nothing during a cold snap, you're past prevention. There's already an ice plug and the section between it and your tap is where the pressure is building.
Leave the tap open — that's the pressure relief — and start warming the area. Do not go at it with an open flame. Every winter someone tries a blowtorch on a pipe in a wall cavity and the call we get afterwards is not a plumbing call.
If you have no water at all, or you can hear water running when everything is shut off, that's the point to stop working through a list and get someone out. Details on what we do and how fast we get there are on the frozen pipe repair page, or the Airdrie version if you're north of the city.
The honest summary
Leave the right taps open during a genuine cold snap. Open the cabinets. Keep the heat on everywhere. Disconnect the hoses in October. Find your shutoff before you need it.
Dripping every tap in the house all winter, on the other hand, is a water bill without a benefit — and worse, it's the kind of thing that feels like you've handled the problem when the bump-out over your garage is still the actual risk.
If you've had a freeze before, in the same spot, that's not bad luck — it's a detail of the house that hasn't been fixed yet, and it's fixable outside of winter for a fraction of what the emergency costs. Call 587-834-3668 and we'll look at where it's happening and why.
