Creosote removal, from a routine brush-out to glazed stage 3 deposits

What you are seeing

These are the signs that the buildup in your flue has gone past what a brush will take off.

• A sweep told you the brush was sliding over something shiny and quoted a different job.
• Black, tar-like drips on the smoke shelf, the damper or the back wall of the firebox.
• The flue looks painted with black glass when a flashlight goes up past the damper.
• A strong tar smell through the house on warm, humid days, with the damper shut.
• You heard a roar or a rumble in the chimney during a fire, and now there are puffy black flakes everywhere.

What we do on a creosote removal visit

Glaze comes off in stages, and the order protects the tile as much as it protects your floors.

1. Camera first, to grade the creosote and find old fire damage

   Before any tool touches the flue, the camera goes up to grade the deposit, measure how far it runs, and look for what glaze hides: cracked or shifted tile, a missing mortar joint, puffed deposits from a chimney fire you may not have noticed. A fire-damaged flue changes the plan.

2. Seal the opening and set up the vacuum

   Glaze removal throws more debris than a sweep, so the firebox is sealed with a panel and the HEPA vacuum runs the whole time. For a stove the connector pipe comes off and the thimble is plugged; for an insert the surround comes off and the unit may come out so the shelf behind it can be reached.

3. Treat the glaze with a chemical modifier

   Third-degree glaze is too hard to brush, so we apply a creosote modifier that reacts with it and turns it brittle or powdery. Some flues respond in hours; others need the product to sit for days, and we come back for the mechanical pass. Between visits the flue stays cold and the damper closed, because treated glaze is still fuel.

4. Run the rotary tools matched to the flue

   A drill-driven flexible rod spins a head sized to the flue: chains for sound clay tile and bare brick, poly whips for a stainless liner that chains would score. We work from the top down in passes, stopping to vacuum and to check the camera, until the tile shows its own color. On soft 1910s brick we slow down rather than cut mortar.

5. Clear the smoke chamber, the shelf and the damper

   The smoke chamber is where glaze often sits thick, on the sloped corbelled brick behind the damper. We scrape it by hand, clear the smoke shelf of fallen chunks, and work the damper plate until it moves and seats. A damper warped by heat gets photographed, because warping means a fire burned hot in there.

6. Camera again, photograph, and write down the cause

   The camera goes back up and the after images sit next to the before images. The note you get names the degree we removed, how far it ran, what caused it as far as the flue tells us, and whether the flue is fit to use, fit after a liner or repair, or stays cold.

The three degrees of creosote, and why the third is a different job

First-degree creosote is dry soot a brush removes, second-degree is a crust that takes a rotary head, and third-degree is a glaze that a brush slides over, which is the line between a sweep and this page.

Glaze forms when smoke condenses on a flue wall, bakes, and takes another layer on top, over and over, until it is a hard, shiny coating. It burns hot, it feeds chimney fires, and it bonds to the tile so a brush polishes it instead of lifting it.

The trade cleans any flue once deposits reach an eighth of an inch. Glaze can reach that thickness in patches long before the whole flue does, which is why the camera decides the job, not a tape measure at the damper.

What makes a Portland flue glaze over

Glaze comes from cool, slow smoke, and in Portland that often means wet wood, an overnight smolder, or a flue that is too big or too cold for what burns into it.

With measurable rain on about 157 days a year, firewood stacked without a roof over it can stay above 20 percent moisture; it steams instead of burning and the steam carries tar up the flue. A stove shut down for the night does the same thing with dry wood.

The flue side matters as much. An insert vented into an open fireplace flue, a cold exterior chimney, and a rough unlined brick flue all cool the smoke before it gets out. A flue like that will glaze again after we clean it, and the remedy is a liner matched to the appliance, insulated where the chimney runs outside the house.

Creosote removal after a chimney fire

If there is a fire in the chimney right now, leave the house and call 911. Afterward, creosote removal starts with a Level 2 camera inspection, because cracked or collapsed tile has to be found before chains go anywhere near it.

A chimney fire burns the glaze itself, and what it leaves is puffy, honeycombed creosote that is light and brittle, plus whatever the heat did to the tile.

The puffed deposits come out easily; the question is what is under them. Cracked tile means a liner before the next fire, and a warped damper or a discolored cap are the outside signs that the fire ran hot. Our chimney fire guide walks through the day after, step by step.

What moves the price of creosote removal

The posted price covers glaze in one flue of ordinary height, and the list below is what takes it higher.

• How much of the flue is glazed: a band above the damper is one job, tile glazed to the cap is another.
• A second visit when the modifier needs days to work before the mechanical pass.
• A stainless liner, which takes slower, gentler tools than clay tile.
• Bare brick and soft mortar in an unlined flue, where we trade speed for the mortar joints.
• An insert that must be pulled to reach the smoke shelf behind it.

Keeping the glaze from coming back

Glaze stays away when the smoke stays hot: split, seasoned wood under 20 percent moisture, hot fires with the air open, and a liner sized to the appliance, and the report names which change your flue needs.

When the cause is wood or habit, the change is yours: split, covered, seasoned wood, hot fires with the air open while the load catches, and no all-night smolder. When the cause is the flue, the change is ours: a liner sized to the appliance, a cap that keeps rain off the tile, or an insert connected to its own liner.

When a repair stops making sense

Removal stops making sense when the flue will glaze again within a season: an insert in an open flue, a cold exterior chimney, or tile cracked by a fire. The honest answer is a stainless liner, and removal becomes step one of that job.

For an unlined brick flue that will not be used again, the simpler honest answer is a clean-out, a cap and a closed damper, and the report says that too.

Related pages

Services, symptoms, fireplace types and guides that connect to this page.