What Time of Year Should You Have a Chimney Swept?

Why spring and summer work so well

Right after the last fire of the season, the year's soot and creosote are still in the flue. Leave them there all summer and humid air brings out a sour, smoky smell that drifts into the room, especially in July and August when the air conditioning pulls air down the chimney. Acidic deposits also sit on the damper and the flue tile for months, and rust starts on cast iron parts.

Sweeping in spring clears that out and leaves the chimney clean for the quiet months. It also means that any problem the inspection finds, such as a cracked crown, a rusted damper or loose flashing, can be fixed in mild, dry weather when masonry and roofing work goes best.

The calendar problem

Almost everyone thinks about the chimney on the first cold weekend of fall, and that is when booking gets hard. A sweep in May, June or August usually means more choice of dates and a crew that is not racing between calls. In the Northeast, that window also avoids the late-fall stretch when rain, early frost and short days make roof work slower.

If you burn wood heavily, a spring sweep has a second benefit: the inspection sees the flue at its worst, right after a full season, which shows exactly how much creosote your burning habits produce.

Early fall: the last good moment

If spring slipped by, September and early October still work. The weather is usually mild, roofs are dry, and you can be ready before the first frost. Try not to wait until the week you want to light a fire. If the inspection finds a problem that needs parts, a liner or masonry work, you may end up without a working fireplace for part of the season, and mortar and crown repairs need temperatures above freezing to cure.

Fall is also when animals look for winter shelter. A sweep that finds an open flue can fit a cap before squirrels and raccoons move in.

Storm season is another reason not to leave it too late. Late-summer and fall storms, and the first nor'easters, test caps, crowns and flashing. A chimney that was checked beforehand is less likely to surprise you with a leak or a blown-off cap in December, when repairs are harder to schedule.

Can a chimney be swept in winter?

Yes. A chimney can be swept any time the appliance is cold. The fireplace has to be out with no hot embers, so most winter sweeps happen in the morning before anyone lights a fire, and a stove is let die down the night before. Roof access in snow and ice is the main limit, which can push the top inspection to a better day. Winter sweeping makes sense in a few situations.

• You burn wood most days and the flue is building creosote fast
• Black flakes are falling into the firebox mid-season
• Smoke has started to roll into the room when it did not before
• You hear animals in the flue or see nest material
• You just bought the house and have not had it checked
• You suspect a chimney fire happened, even a quiet one

Boiler, furnace and water heater flues

Many homes have a heating appliance venting into the same chimney as the fireplace, often in a separate flue. Those flues run on the heating calendar, not the fireplace calendar. An oil boiler leaves soot and scale through the winter, so its flue is commonly cleaned once the heating season ends, or just before the yearly burner service so the technician tunes the flame against a clean flue. A gas appliance makes little soot but still needs its flue checked for debris, tile damage and condensation problems.

A boiler that also makes hot water runs all year, so pick a mild day and expect it to be off for part of the visit.

Timing by appliance

Since one visit can cover every flue in the stack, it is worth telling the sweep what each flue serves when you book. Timing usually works like this for each kind of appliance.

• Open wood fireplace: late spring to early fall, which clears the season's creosote and leaves time for repairs
• Wood stove or insert in heavy use: before the season, plus a midwinter check, since long burns build creosote faster
• Oil boiler or furnace: after the heating season or just before the burner tune-up, since soot and scale collect all winter
• Gas boiler or water heater: any time of year, yearly, to catch debris, nests and condensation damage
• Gas fireplace: before the first cold night, so the vent and burner are checked after sitting idle

Timing versus how often

The season you choose matters less than doing it on schedule. NFPA 211 calls for chimneys, fireplaces and vents to be inspected every year and cleaned when deposits build up, and inspected after a chimney fire or anything else that may have damaged them. Pick a time of year you will remember, tie it to something else on the calendar such as the burner service or the end of the school year, and keep to it.

Not every inspection ends in a full sweep. A lightly used fireplace may show only a thin dry layer, and an honest technician will say so. A family-owned crew that handles the same kinds of houses season after season can tell you whether a sweep is due or whether the inspection alone covers it this year.

Getting ready for the visit

Stop using the fireplace or stove a day before so it is fully cold. Clear the hearth and a path from the door, move fragile items off the mantel, and keep pets in another room. If a boiler shares the chimney, know where its service switch is. Note anything you have noticed during the season, such as smoke spillage, smells or sounds, so the technician knows where to look first.

Afterward, ask for a short written record of what was cleaned and what was found in each flue. Kept with your house papers, it shows the next technician how fast deposits build in your chimney, which is the real answer to how often it needs sweeping. It is also useful to an insurer after a claim and to a buyer's inspector if you sell.