Preventing Frozen Pipes in NYC Basements

Cellars and basements in the city's older housing stock were not built to modern insulation standards, and in most of them they were not insulated at all. The supply lines running along a foundation wall or past an old coal chute are the freeze points we return to every winter, usually in the same handful of spots.

This is about the preparation that keeps that from happening. If a pipe has already frozen or burst, the emergency steps are a separate matter and are covered in our article on why pipes burst during winter.

Find the cold spots before the cold does

Pipes do not freeze because the cellar is cold generally. They freeze because a specific run sits in a specific draft. On a genuinely cold day, walk the cellar and put your hand near the foundation wall at each point where a pipe runs along or through it. The places you feel moving air are the places that will freeze.

The usual suspects in NYC houses are consistent: foundation vents that were never closed after summer, gaps around the old coal chute or cellar hatch, unsealed penetrations where the gas or water service enters, basement windows with failed glazing or missing panes, and the junction where a rear extension meets the original building. That last one catches people, because the extension is often heated to a lower standard than the rest of the house and the pipe feeding the back kitchen runs straight through it.

Sealing beats insulating

Given a choice of one thing to do, seal the drafts rather than wrap the pipes. Pipe insulation slows heat loss; it does not add heat. A wrapped pipe sitting in a stream of 15-degree air coming through a foundation vent will still freeze — the insulation just means it takes slightly longer.

Close and seal foundation vents for the winter. Fill gaps around service penetrations with expanding foam or an appropriate sealant. Repair or temporarily board failed basement windows. Weatherstrip the cellar hatch. None of it is glamorous and all of it does more than the pipe sleeves.

Then insulate, properly

Once the air is not moving, insulation earns its keep. Foam sleeves sized to the pipe are inexpensive and adequate for most runs; the common mistake is leaving gaps at elbows, tees, and valves, which is exactly where the pipe is most exposed. Insulate continuously, including the fittings.

Pay particular attention to any run inside or against an exterior wall, since that pipe has cold on one side and no room air on the other. Where a pipe runs through an unheated crawl space or an uninsulated extension, insulating the space itself is often more effective than insulating the pipe within it.

Heat tape, where insulation is not enough

For a run that has frozen before despite sealing and insulation — a pipe through an unheated garage, an exposed section in a crawl space, a line in an extension that cannot practically be heated — electric heat tape or heat cable is the right tool. Use a product rated for the pipe material, follow the manufacturer's instructions on overlap, and use one with a built-in thermostat so it is not running all winter.

Heat tape needs a working outlet and it fails silently. If you rely on it, check it at the start of each season rather than discovering in January that it stopped working in March.

Before the first hard freeze

• Disconnect garden hoses and shut off and drain the outdoor hose bibs — a hose left attached traps water in the bib and splits it
• Close and seal foundation vents
• Seal gaps at the coal chute, cellar hatch, service penetrations, and any failed basement window
• Insulate exposed runs continuously, including elbows and valves
• Check any existing heat tape actually works
• Confirm you know where the main shutoff is and that it turns
• Keep cellar doors closed so the building's ambient heat stays where the pipes are

During a cold snap

Let a faucet fed by a vulnerable run drip. Open cabinet doors under sinks on exterior walls so room air reaches the pipe behind them. Do not drop the thermostat overnight during a hard freeze — the saving is small and the failure is expensive.

If you have a vacant unit, an empty rental, or a floor you are not using, set the heat low rather than turning it off. Unheated empty units are one of the most reliable sources of burst-pipe calls in two- and three-family houses across Brooklyn and Queens, and the damage almost always exceeds the heating bill that was being avoided.

If it has happened before, it is not bad luck

A cellar that froze last winter has a specific, findable gap — a draft, a missing insulation run, a pipe routed somewhere it should not be. Homes repeat the same freeze in the same spot year after year because the underlying condition never got addressed, only worked around.

That is worth having looked at in the fall, when it is an afternoon's work, rather than in January when it is an emergency and a wet cellar.