Why prewar NYC buildings freeze
New York's older buildings were not built around modern insulation. Risers run up through exterior walls and unheated chases; supply lines hug brick that's twenty degrees colder than the room; brownstone garden floors and cellar pipes sit close to the cold ground and the street. When a polar snap drops the city into the single digits, the cold finds those weak points and the water inside them stops moving. The pipe doesn't have to be outdoors — it just has to be on the wrong side of an uninsulated wall.
The pipes most likely to freeze are the ones nobody is using. Water that's flowing carries a little heat and resists freezing; water sitting still in a line behind a kitchen cabinet on an exterior wall, in a vacant apartment, or in a rarely-used bathroom is the first to lock up. This is why a freeze often shows up at the worst-insulated, least-used fixture in the building rather than the most obvious one.
Brownstones and small buildings have their own exposure: an unheated cellar, a pipe near a drafty bulkhead door, a hose bibb on the back wall that was never shut off and drained for winter. In larger prewar buildings the failure is usually a riser or a branch line in an exterior wall, which means the freeze — and the eventual leak — is shared by a whole line of apartments, not just one.
Prevent it before the cold front arrives
When a hard freeze is forecast, the single most effective move is to keep water moving. Open the affected faucets — both hot and cold — to a thin, steady trickle, especially at fixtures on exterior walls. Moving water is far harder to freeze than still water, and a slow drip overnight costs pennies against a burst pipe. Prioritize the taps farthest from where your water heats, and any fixture you already know runs cold in winter.
Let the warm air reach the pipes. Open the cabinet doors under sinks on exterior walls so room heat circulates around the supply lines hiding behind them. Keep the apartment heated — don't drop the thermostat to save money during a cold snap, and never let an apartment go unheated while you travel in January. If you own a brownstone, close and drain exterior hose bibbs, seal obvious drafts near exposed pipes, and consider foam pipe sleeves on any line you can reach in the cellar.
If you're a tenant in a building that's chronically cold, the freeze risk is also a heat problem — and during heat season the building owes you minimum temperatures. A building that can't hold heat is a building whose pipes are exposed. Our no-heat guide covers the heat-season rules and how to put the landlord on notice; getting the heat fixed is also frozen-pipe prevention. Report cold spots near pipes to the super before the freeze, not after the flood.
You found a frozen pipe — do this now
The tell is simple: you open a tap and nothing comes out, or only a dribble, while other fixtures run fine — and it's cold out. Before you do anything else, find the shutoff for that line and be ready to use it. The danger with a frozen pipe isn't the freeze; it's the thaw, because ice can split the pipe wall and you won't see the leak until the water flows again. Knowing where the valve is now means you can stop a flood the instant it starts.
Open the frozen faucet — both handles. As you thaw the line, an open tap gives the melting water and the pressure somewhere to go, and the first trickle tells you the ice is releasing. Leave it open the whole time you work. Then locate the frozen section: follow the dead line toward the exterior wall it runs along, and feel for the coldest stretch, or look for frost or a faint bulge on an exposed pipe in the cellar or under the sink.
In an apartment, loop in the super early. If the frozen line is a riser or sits inside the wall, it's the building's pipe and the building's access — and a frozen riser is everyone's problem on that line. Building staff can shut the riser, reach the basement, and get into the apartments above and below. You handle the exposed pipe under your own sink; the super handles anything in the walls or shared.
Thaw it safely — and what never to use
Apply gentle, even heat to the frozen section with the faucet open. A hair dryer worked slowly back and forth along the pipe, a heat lamp or space heater kept a safe distance away, or towels soaked in hot water and wrapped around the line all work. Start near the faucet and move toward the cold spot, so meltwater can drain out the open tap instead of getting trapped behind more ice. Patience matters more than power here.
Never thaw a pipe with an open flame. A blowtorch, a propane torch, or any open fire is how frozen-pipe calls become fire-department calls — torches ignite wall framing and old finishes, and they heat the pipe so unevenly it can rupture on the spot. Don't use a torch even on an exposed metal pipe in a cellar. The slow methods cost you twenty minutes; the fast one can cost you the building.
Watch the pipe as it thaws, because this is when a freeze-damaged line reveals itself. If water starts spraying or weeping from the pipe as the ice releases, shut that line's valve immediately and switch to our burst-pipe playbook for the next ten minutes. If you can't find the frozen section, can't reach it safely, or the pipe is inside a finished wall, stop and call a licensed plumber — opening a wall to chase a frozen line is their work, not a DIY afternoon.
The signs it's about to burst
Some frozen pipes give warning before they fail. A pipe that's visibly bulging, split, or beaded with frost has likely already been stressed by expanding ice, and the moment it thaws it may let go. Strange sounds when you run nearby water — banging, whistling, or a sudden change in pressure across the apartment — can mean ice is partially blocking a line and the pipe is under strain. Treat any of these as a pipe telling you it's close to the edge.
If you suspect a pipe is on the verge, don't force a thaw and walk away. Keep the valve within reach, keep the affected faucet open, and apply heat slowly while you watch. If the freeze is in a wall, a riser, or anywhere you can't monitor the pipe directly, the safe move is to get the line shut and a plumber dispatched rather than gamble on an unattended thaw. A controlled shutoff beats a 3 a.m. ceiling collapse every time.
Know your worst case so you can react without hesitation: a burst supply line pushes water continuously until someone closes a valve, and in a stacked building that water finds the units below. If your frozen pipe sits above finished space — yours or a neighbor's — assume a thaw could flood downward and have the shutoff and the super's number ready before you apply the first bit of heat.
Who to call — and how Reset helps in a freeze
Call a licensed plumber when the frozen pipe is inside a wall, when it's already split or leaking, when you can't safely reach or thaw it, or when it's a building riser the super needs help with. In NYC, anything beyond thawing the exposed line under your own sink — opening walls, replacing a burst section, working on a riser — is licensed work that belongs to a Licensed Master Plumber. Our guide to verifying a plumber's license shows how to check any license number against the public DOB roster in about two minutes.
A freeze rarely hits one apartment alone, which is what makes a hard cold snap a brutal night to find a plumber: the whole city is calling at once. Reset's board shows which licensed plumbers can actually move right now, with price bands and published trip fees shown before you book — so a 2 a.m. freeze is a comparison, not a phone tree. Every profile is verified against the DOB roster, and when Reset's own crew takes the job it's labeled In-House, never disguised as an independent shop.
If it's an emergency — a pipe that's burst, or one about to — the Reset Guarantee applies: emergency requests are confirmed within 30 minutes, or Reset's in-house crew is dispatched automatically. Reset covers the Bronx, Manhattan, Brooklyn, and Queens today, with Staten Island opening later in 2026. We're a young network recruiting our Founding 50, so the roster is honest rather than padded — but on the coldest nights, that's exactly when knowing someone real is on the way matters most.