How NYC weather affects your apartment: a season-by-season cleaning guide

Heat season: October 1 to May 31, by law

New York City's heat law requires residential buildings to provide heat from October 1 through May 31 — at least 68°F inside during the day whenever it drops below 55°F outside, and 62°F at night no matter the outdoor temperature. In a steam-heated building, that means your radiators run for eight months of the year. And for those eight months, they drive the convection currents that pull dust through the apartment, bake it onto the fins, and redistribute it around every room.

Steam heat also dries the air out — in a January cold snap, indoor humidity in a radiator-heated apartment can fall into desert range. Dry air keeps dust airborne longer and adds static, which is why it clings to screens and dark furniture all winter. Two things help more than any amount of extra dusting: clean the radiators in September, before the heat comes on and the summer's dust gets baked on, and run a humidifier toward 35–40% humidity so dust settles instead of circulating.

One more heat-season habit: after cold nights, check the sills of single-pane windows. Warm interior air condenses on cold glass, water pools on the sill, and by March you have mildew speckling in the paint. A ten-second wipe after a cold night prevents a spring repaint.

Winter: salt season is floor season

From November to March, every sidewalk in Manhattan is dressed with rock salt and calcium chloride, and a share of it comes home on your shoes. The white haze it leaves isn't ordinary dirt: dry mopping won't lift it, calcium chloride residue stays faintly tacky and attracts more grime, and ground underfoot the crystals work like fine sandpaper on a floor finish. The six feet inside your front door take a whole winter's worth of that wear.

The fix happens at the door, not after the fact: a stiff-bristle mat outside, an absorbent washable mat inside, and a boot tray so wet soles aren't parked on hardwood. Then damp-mop the entry zone weekly through the winter with a pH-neutral cleaner — if a white film survives the first pass, that's salt residue, not dirt, and a second pass with plain water and a well-wrung mop takes it off. On original pre-war floors, don't let salt slush sit; the standing-moisture rules from our pre-war floor care section apply double in January.

Spring: plane-tree pollen and the open-window trap

The first 70-degree week of spring, the whole city throws its windows open — which is exactly when the London plane trees, Manhattan's most common street tree, release their pollen. From late April into May, that's the yellow-green film that appears on sills, sticks to window screens, and smears instead of lifting when you dry-dust it. Right behind it comes the fluff from the trees' seed balls, which drifts through any open window and collects along baseboards.

During those weeks: keep screens in even when it's beautiful out, and wipe sills with a damp cloth weekly — pollen is sticky, so dry dusting just spreads it. And time your spring deep clean for after the pollen peak, not before. A deep clean in mid-April looks wonderful for about a week; the same clean in late May resets the apartment for the whole summer. That's when we book them for our own recurring clients.

Summer: humidity is a cleaning problem, not just a comfort problem

Once indoor humidity sits above roughly 55–60% — most of July and August in New York — two things wake up: dust mites, which thrive in humid textiles, and mold, which gets its foothold in bathroom grout and caulk lines. Pre-war apartments have it hardest, because many pre-war bathrooms have no exhaust fan at all — a window or an air-shaft vent is the only ventilation, and on a still August day neither moves much air.

The routine that works: after showers, leave the bathroom door open and the window cracked; squeegee the tile if your bathroom is mold-prone. Check caulk lines monthly through the summer — pink or black speckling caught in its first weeks wipes away with a bathroom cleaner, but mold that's colonized the caulk itself has to be recaulked, not scrubbed. No amount of cleaning fixes caulk that's gone dark all the way through.

Window air conditioners deserve their own line item. A window unit recirculates your room air through its filter dozens of times a day — a clean filter is a dust trap working for you, a dirty one is a dust distributor. Most filters slide out from behind the front grille and rinse clean under a faucet in five minutes; do it monthly in season. Wipe the intake grille while you're there, and check that the unit tilts slightly outward so condensation drips outside, not into the wall or down your sill.

All year: avenue soot doesn't take a season off

One Manhattan constant ignores the calendar entirely: traffic soot. If your windows face an avenue or a bus route, the black film on your sills is oily exhaust particulate, and it lands every day of the year. It needs a degreasing wipe — warm water with a drop of dish soap — not a dry dust, and it rewards a weekly cadence over a monthly scrub. The full technique is in our pre-war cleaning guide, and it applies to new construction just as much.

The seasonal calendar we build for recurring clients

Put together, the year looks like this — it's the rhythm we build into recurring plans, and you can run it yourself between professional visits:

• September: radiator and heat-prep clean — fins, behind the units, window gaskets — before the October 1 heat comes on.
• November–March: weekly damp-mop of the entryway to keep salt off the floor finish, on top of the normal cleaning rhythm.
• Late May: the spring deep clean, timed after plane-tree pollen peaks — windows, screens, sills, and everything heat season left behind.
• July: AC filter rinse, bathroom caulk-and-grout check, and a look inside closets and under-sink cabinets for humidity trouble.
• Every week, all year: a damp wipe of avenue-facing sills. Two minutes that keeps soot from becoming a scrubbing job.

A schedule beats a heroic clean

The pattern in all of this: Manhattan apartments don't get dirty randomly, they get dirty on a schedule — so the cleaning has to run on one too. A single deep clean fixes a moment; a calendar fixes the year. That's the thinking behind our recurring plans, and you can see what the switch looks like in practice in our West Village family reset case study, where the fix wasn't one heroic clean — it was a system.