How long and how cold
An Arctic front on Saturday, February 7, 2026 brought a dusting of snow, wind gusts past 45 mph and a falling temperature all day. On February 7 and 8, Central Park, LaGuardia, JFK, Newark, Islip, White Plains and Bridgeport all recorded single-digit lows on two days in a row, which had not happened since January 30 and 31, 2019. Central Park reached 3 degrees on Sunday morning.
The bigger number is the length of the cold. Across the 16 days from January 24 through February 8, the city's mean temperature stayed under 20 degrees. The last 16-day period that cold was January 11 to 26, 1982. Ice filled the Hudson River even south of the George Washington Bridge. Earlier in the stretch, January 31 had marked the eighth straight day with highs below freezing.
Sixteen days of boiler exhaust
In most brownstones, rowhouses and small apartment buildings, heat comes from an oil or gas boiler venting into a brick chimney. In a mild week that boiler cycles on and off. In a stretch like this one it barely rests. Every hour of firing sends hot, wet exhaust up the flue.
When the flue is the right size and lined, that exhaust stays warm enough to leave the top as vapor. When the flue is an old, oversized clay or bare brick passage, often built for a coal furnace, the gases cool on the way up and the water condenses on the walls. Condensate from gas and oil combustion is acidic. Over seasons it softens mortar joints, cracks clay tiles and leaves a crust of debris at the base of the chimney.
Heat loss up the chimney adds to the effect. A tall masonry chimney on an outside wall cools quickly in hard cold, and the flue walls can stay below the temperature at which water vapor condenses for much of the run. That is why condensation problems often appear first after a long cold spell rather than after a single frigid night.
Signs that the cold did damage
Look for stains or peeling paint on the chimney breast inside the house, a white or brown streak on the outside brick near the top, small piles of clay or mortar in the cleanout, and rust at the breach where the boiler pipe enters the chimney. A boiler that tripped off on a safety switch during the cold, or a technician who found poor draft, is also worth noting. Each of these points back to a flue that is losing the fight with condensation.
Where this leads
A flue that is too large or deteriorated for the appliance it serves is usually corrected with a properly sized liner, often stainless steel, run from the appliance connection to the top. That keeps exhaust warm, protects the masonry and gives the boiler a steady draft. It is a common job in older city buildings after a hard winter exposes the problem.
Want a professional look? See our boiler chimney relining service, or call (844) 468-2410 for a free written estimate.
