Two numbers answer the question. A chimney should be inspected once a year, and it should be swept when the soot on the flue wall is an eighth of an inch thick. For a fireplace lit on a few winter weekends, that can mean an inspection every year and a sweep less often. For a wood stove that runs every evening from November to March, it can mean a sweep every year and a mid-season check on top. The rest of this article explains where the two numbers come from and how they fit the way people on the peninsula burn.
Where the rule comes from
CSIA, the Chimney Safety Institute of America, reproduces the relevant line of NFPA 211 for homeowners: a yearly inspection at minimum, looking at soundness, at deposits and at clearances. CSIA then gives the threshold for cleaning a masonry fireplace, which is an eighth of an inch of sooty buildup. Shiny, tar-like glaze is a reason to act sooner, at any thickness.
Washington's own fire officials say the same thing in fewer words. The State Fire Marshal's Office issued its home-heating warning on September 21, 2026. It reports six lives lost in Washington during the preceding year to fires that began with a home heating source, and it asks residents to get the chimney inspected and cleaned each year.
So the interval is not really a number of months. It is a measurement, taken once a year by someone who can see the whole flue.
Matching the rule to how you burn
The table applies the two numbers to the situations we meet most. The right-hand column is a starting assumption, and the soot measurement at the visit always overrides it.
A flue with an unknown past is the one case where we do not start with a brush. A camera inspection comes first, because sweeping tells you nothing about the tiles behind the soot.
| How the appliance is used | Inspection | Sweeping |
|---|---|---|
| Open fireplace, a few fires each winter | Every year | When soot reaches 1/8 inch; often not every year |
| Open fireplace, most weekends in the cool season | Every year | Expect it yearly |
| Wood stove or insert burned daily | Every year, before the season | Yearly, with a mid-season look if the glass blackens fast |
| Fireplace kept as backup heat for outages | Every year | By measurement; keep it ready before storm season |
| House just bought, burning history unknown | Before the first fire, with a camera | Decided by what the camera shows |
| Gas appliance on its own vent | Every year | Rarely needed; the vent is checked for blockage |
How wood is actually burned on the peninsula
Census figures explain why the first row of that table is the common one. Across Seattle, the American Community Survey finds that wood is the principal heating fuel for roughly 0.2 percent of occupied homes; electricity and utility gas together heat more than nine in ten. In the ZIP code areas that cover West Seattle, very few homes report wood as their main heat, and the margins of error on those small estimates are wider than the estimates. The survey asks only about the primary fuel. It does not count fireplaces at all.
Read together, those figures describe a place where a wood fire is nearly always a choice for the evening and not the furnace. That lowers the soot load. It does not lower the need to look, since a flue that sits cold and damp for ten months has its own problems.
Outages are the exception to the occasional-use pattern. The gale of December 2006 left 49 percent of City Light's customers in the dark, and the city's hazard analysis records that people in King County died from burning charcoal indoors to keep warm. A fireplace that has been inspected is a far better plan than that, which is one reason to have the visit done before the windy months and not after the first storm.
Habits that stretch or shorten the interval
What you burn decides how fast the flue coats. Only two fuels are allowed by the Clean Air Agency in a household fireplace or stove: dry, seasoned firewood and manufactured logs. Ban or no ban, the agency's opacity rule applies: chimney smoke denser than 20 percent, held that way for six minutes running in an hour, is a violation. Thick smoke is fuel that left the firebox unburned, and part of it condenses on the flue wall on the way up. A fire that burns clean enough for the agency's rule also leaves less behind for the brush.
Burn bans work the other way on your planning. The agency calls them mostly in cold, still fall and winter weather, the very evenings a fire is most tempting. During one, the fireplace stays unlit unless the home holds an approved exemption.
When to book, and what a sweep runs
On WeatherSpark's Seattle profile the cool months run from November 12 to March 1, and the wetter season is under way by October 10. Late summer and early fall are the sensible window: nothing has been burned for months, the roof is dry, and if the visit turns up a cracked crown or open mortar joints there is still dry weather to repair them.
Our sweep is $189 to $449, with the low end for a straight flue on an easily reached roof and the high end for steep roofs and difficult access. When only a look is needed, the inspection is $99 plus tax per chimney, deducted from any work you approve afterwards.
For reference, Jason L. Chimney Co., which gives an address on SW Admiral Way, lists a standard sweep at $150 to $250 on its pricing page. HomeBlue's Seattle estimate, on a page dated June 3, 2024, is $160 to $180 for one chimney.
Frequently asked questions
We light the fireplace a handful of times a year. Is a yearly visit still worth it?
The yearly item is the inspection, not necessarily the sweep. A flue that sees five fires may not reach an eighth of an inch of soot in a year, and we will tell you so. What a lightly used chimney does collect is everything unrelated to burning: a nest, a cracked tile, a cap knocked loose by a branch, water from a failing crown. Those are found by looking, and they matter the first evening you light a fire.
Does sweeping let me burn during a burn ban?
No. A burn ban is about the air outside, not about your flue. Under Stage 1 of the Puget Sound Clean Air Agency's bans, an open wood fireplace may not be lit, and neither may a stove or insert without certification; When Stage 2 is called, the ban also takes in certified appliances and stoves that burn pellets. The only households exempt are those the agency has approved as lacking any other adequate heat source, and even they must keep the chimney from showing smoke.
What should I do with the ashes between sweeps?
The State Fire Marshal's Office, in its release of September 21, 2026, advises putting ashes in a metal container with a lid and keeping that container outdoors. Ash holds live embers far longer than it looks. Do not use a paper bag, a plastic bucket or the garage.
Does a gas fireplace vent need the same attention?
It needs the yearly look. The NFPA 211 wording that CSIA quotes covers chimneys, fireplaces and vents alike. Gas does not leave the soot that wood does, so the eighth-of-an-inch rule seldom comes into play, but a vent can still be blocked, disconnected or corroded.
Sources
- CSIA — homeowner resources page — accessed October 4, 2026
- State Fire Marshal — home heating safety (Sept. 2026) — accessed October 4, 2026
- Census Reporter — ACS 2020–2024, heating fuel (B25040) — accessed October 4, 2026
- Seattle emergency management — windstorms analysis — accessed October 4, 2026
- PSCAA — legal overview of wood burning — accessed October 4, 2026
- Clean Air Agency (Puget Sound) — the two ban stages — accessed October 4, 2026
- WeatherSpark — Seattle, average weather — accessed October 4, 2026
- Jason L. Chimney Co. — 2026 price guide — accessed October 4, 2026
- HomeBlue — chimney sweep estimate, Seattle — accessed October 4, 2026
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