How to read this chimney parts glossary
Start at the cap and read down: that is the order in which rain, animals and a sweep’s brush meet the parts, and the order an inspection report lists them.
Most of these words first come up during a chimney inspection, and the inspection levels guide explains the report they land in.
At the top of the chimney
The top of a chimney has one job in Portland, keeping about 37 inches of rain a year out of the brick and the flue, and five parts share it: the cap, spark arrestor, crown, chase cover and top-sealing damper.
| Part | What it is and what it does | Connects to |
|---|---|---|
| Cap | A metal hood over the flue opening that keeps rain, leaves and animals out while smoke leaves freely. Stainless steel lasts; galvanized rusts. | Water in the firebox; chimney cap installation |
| Spark arrestor | The wire mesh on the sides of a cap. It stops embers leaving and birds entering; mesh that is too fine clogs with creosote. | A clogged screen reads as smoke coming into the room |
| Crown | The sloped concrete slab over the top of the masonry around the flue, shedding water off the brick. It cracks from freezing water and thin construction. | Cracked chimney crown; chimney crown repair |
| Chase cover | The sheet metal lid on the framed chase of a factory-built fireplace, the crown’s counterpart. A flat one ponds water and rusts through. | A factory-built fireplace item; rust streaks on the siding |
| Top-sealing damper | A gasketed lid at the top of the flue, worked by a cable from the firebox. It seals far tighter than a throat damper and doubles as a cap. | Cold draft from the fireplace; damper repair and replacement |
Where the chimney meets the roof
The joint between chimney and roof is the hardest one on the house to keep dry, because two materials that move differently meet there under running water.
| Part | What it is and what it does | Connects to |
|---|---|---|
| Flashing | L-shaped metal pieces woven into the shingle courses and turned up against the chimney, carrying roof water around the stack. | Water leaking around the chimney; chimney flashing and leak repair |
| Counter flashing | A second metal layer set into a mortar joint and bent down over the base flashing, so water on the brick cannot get behind it. | Ceiling stains after wind-driven rain |
| Cricket | A small peaked saddle on the uphill side of a wide chimney that splits water and debris around it instead of letting them pond. | Leaks only in heavy rain on a wide chimney |
| Chase | The framed, sided box around a factory-built fireplace’s metal pipe. Carpentry, not masonry; it rots from the top when the cover fails. | Soft siding on a prefab chimney |
Inside the stack
The stack is a passage, and every part here is about keeping heat and gases inside it and water out of the brick around it.
| Part | What it is and what it does | Connects to |
|---|---|---|
| Flue | The passage from the smoke chamber to the cap that smoke and gases rise through. One chimney can hold several, each serving one appliance. | Sized to the appliance; an oversized flue runs cold |
| Flue liner | The inner wall of the flue, separate from the structural brick, that keeps heat and gases off the masonry: clay tile, stainless steel or a cast-in-place mix. | Chimney liner installation |
| Clay tile liner | Fired-clay sections about two feet long, stacked and mortared, and a very common liner in American chimneys. Tiles crack from chimney fires, settlement and water. | Cracked tiles on a Level 2 scan; an unlined brick chimney has none |
| Stainless liner | A flexible or rigid stainless tube run down an existing flue and connected to the appliance, often insulated, giving an unlined or damaged flue a continuous passage of the right size. | Inserts, stoves and the flue a new furnace leaves behind; see the orphaned chimney guide |
| Mortar joints | The beds of mortar between the bricks, softer than brick on purpose and the first thing to weather. Open joints let water in and, on an unlined chimney, gases out; tuckpointing grinds them out to a set depth and repacks them. | Loose or missing mortar; tuckpointing and masonry repair |
The throat, between the firebox and the flue
Between the firebox and the flue sits the throat, where smoke turns a corner, and many draft problems and odor complaints begin right there.
| Part | What it is and what it does | Connects to |
|---|---|---|
| Damper | The movable metal plate that closes the flue when the fireplace is cold, so heated air stays in the house. Open before lighting, closed only after the ashes are cold. | Left shut, it sends smoke and carbon monoxide into the room; damper stuck or won’t close |
| Throat damper | The common type: a cast iron plate on a hinge or rod just above the firebox, worked by a handle or chain. Rust, warping from a chimney fire and fallen debris jam it. | Freed, or replaced by a top-sealing damper |
| Smoke shelf | The flat ledge behind the damper that catches rain and debris coming down and turns downdrafts back up. It fills with wet soot. | Where a fireplace smells bad after rain starts |
| Smoke chamber | The inverted funnel above the damper that gathers smoke from the wide firebox into the flue. Its stepped brick catches creosote and slows the draft unless parged smooth with refractory mortar. | Smoke chamber and firebox repair |
The firebox, the hearth and what sits beneath them
The firebox takes the heat, the hearth takes the sparks, and the parts beneath them carry the ash away; this is the part you can inspect yourself with a flashlight.
| Part | What it is and what it does | Connects to |
|---|---|---|
| Firebox | The chamber where the fire burns: firebrick in a masonry fireplace, a metal shell with refractory panels in a factory-built one. | Repaired along with the smoke chamber |
| Firebrick | Dense, pale, heat-resistant brick laid with thin refractory mortar joints to line the firebox. Ordinary red brick spalls in that heat. | Rust on the damper or firebox means water is reaching it |
| Refractory panel | The molded, cement-like panels lining the firebox of a factory-built fireplace. Hairline cracks are normal; cracks you can see through, or crumbling, mean replacement before the next fire. | Replaced panel by panel |
| Hearth | The noncombustible floor of the fireplace and its extension into the room, brick, stone or tile over a slab, that catches sparks. | A Level 1 item; a wood stove needs its own floor protection |
| Ash dump | A small metal door in the firebox floor that drops ash into a pit below, reached from the basement or the outside base of the chimney. | A draft and odor path when open over a full pit |
| Cleanout door | The small iron door at the base of the chimney, outside or in the basement, opening into the bottom of the flue or the ash pit. It must close tightly. | Checked on every chimney sweep; missing, it is a draft and carbon monoxide path |
Stove and insert parts
Wood stoves and inserts bring four parts of their own, the thimble, connector pipe, baffle and catalytic combustor, and a stove sweep spends most of its time on the pipe and baffle.
| Part | What it is and what it does | Connects to |
|---|---|---|
| Thimble | The lined opening through a wall or chimney breast that a stove’s connector pipe passes through, holding the hot pipe a set distance from framing and plaster. | A Level 1 finding on a wood stove when packed or unlined |
| Connector pipe | The single or double wall black stovepipe from the stove’s flue collar to the thimble or chimney. Short, few elbows, seams up; brushed on every stove sweep. | Wood stove and insert sweep |
| Baffle | A plate or row of firebrick inside the top of a stove or insert that makes smoke take a longer path over the fire. Fly ash piles on it and chokes the outlet. | Cleaned on a stove sweep; sagging means a stove run too hot |
| Catalytic combustor | A ceramic honeycomb coated with a metal catalyst, in some stoves, that lets smoke burn at a lower temperature than flame needs. Ash clogs it and burning trash poisons it. | Smoky output from a stove or fireplace insert that used to burn clean |
What a sweep finds and names
The last five terms are findings rather than parts: the three degrees of creosote and the two signs of water that every inspection report uses.
| Term | What it is | Connects to |
|---|---|---|
| First degree creosote | Dry, flaky or powdery soot from a hot, well-aired fire. It brushes off with ordinary rods and is what a yearly sweep removes once it reaches an eighth of an inch. | A routine sweep; see the creosote stages guide |
| Second degree creosote | Harder, crunchy flakes or tar-like scales from smoldering fires or wood that was not dry. Stiffer brushes or a rotary head take it off. | Wet wood and shut-down air; see seasoned firewood |
| Third degree creosote | A shiny, hard, tar-like glaze baked onto the liner from repeated cool, smoky, air-starved fires. It is the fuel most chimney fires burn, and brushes will not move it. | Black shiny creosote in the flue; creosote removal |
| Efflorescence | A white, powdery mineral deposit on the face of the brick, left when water moves through the masonry and evaporates. The powder is harmless; the water is the problem. | White stains on chimney brick |
| Spalling | The face of a brick flaking off, usually because water soaked in and froze, which happens on about 32 nights a year at Portland’s airport. Once the face is gone, the core weathers fast. | Spalling or crumbling brick; chimney waterproofing once repaired |
The three parts that matter most for safety
If you remember three words, make them liner, damper and cap: the liner keeps gases in, the damper decides whether they reach the room, and the cap keeps out the water that wrecks both.
A chimney fire in progress is not a glossary question: get everyone out and call 911, and leave the flue cold until a Level 2 inspection has seen it. A carbon monoxide alarm on the same floor as the appliance covers the quieter failures, the blocked flue or shut damper the CDC warns about.