Chimney safety
A chimney is combustion infrastructure that lives outside in one of the wettest climates in the country. This guide covers what actually fails, in what order, and which checks prevent it — methodically, with no scare tactics.
Strip away the ambiance and a fireplace is a controlled fire inside your house, with one exhaust path. That path has a job specification: contain heat, carry flammable creosote and toxic combustion gases up and out — every burn, without exception. When a component fails the spec — a cracked liner, a blocked flue, a missing cap — the failure modes are two: a chimney fire, or carbon monoxide re-entering the house.
The local inputs make the math specific. From the Sammamish River valley up to the plateau, chimneys sit under Pacific Northwest rain for most of the year; on the plateau, winter freeze events turn that absorbed water into cracked crowns and spalled brick. Redmond's 1960s-80s housing stock adds original clay liners nearing end of life, while the wood stoves working through Duvall and Carnation farm winters build creosote faster than occasional-use fireplaces. Every one of those risks is predictable — and a yearly inspection plus a few sound repairs prevents essentially all of them. Here is the checklist.
Start here
The national fire-safety standard, NFPA 211, calls for every chimney, fireplace and vent to be inspected at least once a year. The reasoning is structural: the components that fail — liner interior, crown, flashing — are exactly the ones invisible from the floor. A proper chimney inspection runs a camera through the full system and converts unknowns into a documented, prioritized list.
On cost-benefit alone it is the best line item of the year: one visit confirms the flue is clear and the structure is sound before the first cold-season fire.
The #1 fire risk
The chemistry is constant: wood smoke cooling inside a flue deposits creosote, a highly flammable tar residue. It progresses through three stages, and difficulty of removal rises with each one. Glazed Stage 3 buildup can ignite into a chimney fire hot enough to crack a liner in minutes — in the Duvall and Carnation valley, where wood stoves run all winter, buildup reaches that point faster than most owners expect.
Seasoned, dry wood slows the deposition rate; nothing stops it. Scheduled creosote removal and a routine chimney sweep keep the flue below the danger threshold — which is the entire objective.
The invisible risk
CO is colorless and odorless — you get no warning from your senses. A blocked or cracked flue can route it back into the house, so the defense is layered: sound liner, clear flue, working CO alarms on every level.
Carbon monoxide, in detail
Every fuel-burning appliance on the property — wood stove, gas fireplace, furnace or water heater venting through the chimney — produces carbon monoxide as a byproduct. In a healthy system, the flue carries it out. The failure cases are specific: a flue blocked by a nest, a passage choked with creosote, or a cracked liner leaking gases into a wall cavity. Because no human sense detects CO, the mitigation is redundant by design — a clear, correctly sized flue, an intact liner, and a working CO alarm on every floor and near sleeping areas. Test the alarms when the clocks change, and never run a fuel-burning appliance on a flue you suspect is blocked. No exceptions to that last rule.
Rain-driven wear
Brick and mortar are porous — over a wet season that runs most of the year, they load up with water like a sponge. When temperatures drop, that water freezes, expands, and breaks the masonry from the inside: the freeze-thaw cycle. On the Sammamish plateau, which sits higher and freezes harder than the valley floor, the cycle runs more times per winter — and on 1960s-80s chimneys, it works on mortar that is already decades old.
Caught early, the fix is bounded and predictable: masonry repair — repointing joints or recasting a crown. Left alone, water keeps advancing until it reaches the flue. A breathable waterproofing treatment is the most cost-effective way to slow the clock.
The flue's last defense
The liner is the sleeve that keeps heat and combustion gases inside the flue. In the tech-era neighborhoods of Redmond and the older valley farmhouses, that liner is often the original clay tile — a material that cracks with age, with moisture, and immediately after any chimney fire. An undersized or deteriorated liner leaks heat toward framing and gases toward living space.
That makes a cracked liner a safety finding, not a cosmetic one. When inspection verifies liner damage, chimney relining with a correctly sized stainless liner restores both the barrier and the draft — measured, not guessed.
Keep the weather out
Rank chimney enemies by damage caused and water wins. An open or rusted-out flue takes months of Pacific Northwest rain straight down onto the liner and damper; failed flashing routes it into the ceiling and walls instead. A stainless chimney cap closes the opening, arrests sparks, and keeps out the birds and squirrels that block a flue — from the wooded lots around Bear Creek to the pastures outside Carnation, nesting is a routine and genuinely dangerous find.
Stay in your lane
A short list of habits keeps the system safer between visits. Everything touching the flue, the roof or fuel connections belongs to trained hands with the right tools.
Before the first fire
Late summer or early fall, before the calendar fills — so any repair completes before you need to burn.
Reset the buildup to zero so the season starts with a clean flue and a strong draft.
Cap intact, crown uncracked, flashing sealed — the three checkpoints that decide whether rain gets in.
Fresh batteries, then a live test of smoke and CO alarms on every level and near bedrooms.
Seasoned, dry hardwood only. Wet or green wood smolders, cools the flue and lays down creosote fast.
Keep reading
Methodical, no-pressure references on keeping a chimney safe, efficient and watertight through a Sammamish valley wet season.
Common questions
Peace of mind starts here
Pick a verified open slot on the crew calendar. Redmond Chimney Pros photographs every checkpoint — no payment to book, and work only starts if you approve the written quote.
