Black stains above the fireplace opening

What the stain is a record of

The masonry just above a fireplace opening sits directly in the path of anything that escapes under the lintel, the steel angle or arch that carries the brick over the opening. Warm smoke that gets out there rises against the face, cools as it touches the brick, and drops fine carbon into the pores. A single puff leaves almost nothing. A season of small puffs builds the gray-to-black fan that many people first notice when they repaint or hang something over the mantel.

So the brick is the witness, and the smoke is the event. The stain cannot tell you on its own why smoke chose the room over the flue, but it narrows the list, especially when you pair it with what you remember about the fires that made it.

Reading the shape and position

A narrow plume centered over the opening

A tight, central smudge usually comes from short bursts of smoke rather than a steady leak. The most common moment is lighting: a flue full of cold air resists moving until the fire warms it, and the first smoke rolls forward. Reloading a hot fire with an armload of wood, or building the fire close to the front of the firebox, can do the same thing.

A band across the full width of the lintel

An even band from one side of the opening to the other points to a low, steady spill that lasts through the fire. That pattern fits a chimney that never quite pulls enough for the size of the opening, a damper that does not open all the way, or a house that keeps drawing air in through the fireplace while it burns.

Darker on one side

A stain heavier at one corner often follows air moving across the room: a nearby doorway, a stair, a return grille or a ceiling fan. A fire built off to one side, or a damper plate that sticks partly closed on one end, can also tip the spill toward a corner.

Soot that reaches the mantel or ceiling

When the dark area climbs past the mantel shelf, the escapes are larger or more frequent. Check the mantel itself while you are looking. Darkened or scorched wood close to the opening is a heat and clearance question as well as a soot one; see clearances to combustibles.

Soot above gas logs or a gas fireplace

Gas flames are expected to burn far cleaner than wood, so treat soot here as a burner problem first. Vented decorative logs are a partial exception. One vented log manufacturer, Mason-Lite, states in its manual that the realistic flame of a log burner produces carbon monoxide and soot, that soot builds up on the logs when they are not set in the positions shown in the instructions, and that the damper must be fully open and any glass doors open while the logs burn. A sealed direct-vent fireplace or insert should not be leaving soot on the wall at all. In either case, turn the appliance off and get it looked at before the next use. Our guide to film and soot on gas fireplace glass explains the difference between harmless white film and sooting.

Keep notes over the next few fires

Before anyone climbs a ladder, a few evenings of observation will tell you more than the stain does. Photograph the stain with a tape measure beside it so you can compare later, or clean a small test square as described below. Then, for three or four wood fires, jot down:

• When smoke appeared: only while lighting, while adding wood, throughout, or as the fire died down.
• The damper: whether the handle or cable was at its fully open stop.
• The house: whether the range hood, bath fans or clothes dryer were running, and whether any window was open.
• The weather: calm, windy, mild or very cold.
• The wood: how long it had been split and dried. EPA's Burn Wise program puts the target at under 20 percent moisture content, measured with a moisture meter.
• The fire: a small hot fire or a large smoky one. Burn Wise also favors hot fires, since smoldering is unsafe and wasteful in most appliances.

Patterns matter more than any single fire. If smoke appears only during lighting, the step-by-step checks in why smoke comes into the room and why a fireplace won't draw will take you further.

The usual drivers behind the stain

A flue that is slow to warm

A chimney pulls because the hot gas in it is lighter than the outside air. Until the column warms, the pull is weak. Chimneys on outside walls and flues that are tall and cold take longer to get going, which is why the plume-at-lighting pattern is so common.

The house pulling the other way

CSIA describes how a house that exhausts enough air ends up under negative pressure, so air is drawn down a chimney and smoke follows it. Its preferred remedy is make-up air for the house. Exhaust fans and dryers that run while the fire burns are the everyday version of this problem.

An opening that is large for its flue

The Brick Industry Association's fireplace design note sizes the flue from a chart that uses both the area of the opening and the overall height of the chimney. It also calls for the throat to sit at least 8 inches above the highest point of the opening and for a throat damper with an open area about twice that of the flue. When those proportions are off from the start, or a later change alters them, smoke tends to spill at the top of the opening. Raising the hearth, enlarging the opening during a remodel, or leaving a small liner in place after an appliance is removed are the kinds of changes worth mentioning to whoever inspects it.

Something in the way

A damper that no longer opens fully, debris or a nest on the smoke shelf, a clogged cap screen and heavy deposits in the flue all shrink the path. These tend to show up as a fireplace that used to burn cleanly and has started staining.

Cleaning the stain without damaging the brick

Brick around a fireplace is often softer and more porous than people expect, and aggressive cleaning can leave a scar that looks worse than the soot. Work only on a cold fireplace with no hot ash.

1. Lift loose soot dryVacuum with a soft brush attachment before using any water. A federal preservation procedure for smoke stains on brick from the U.S. General Services Administration warns that cleaning can drive stains deeper into porous masonry, so get the loose material off first.
2. Test a hidden spotThe Brick Industry Association recommends a trial clean in an inconspicuous area before treating a whole surface. Let the test area dry fully and judge it in daylight.
3. Scrub gentlyFor smoke, the BIA's cleaning note says scrubbing with scouring powder, particularly one containing bleach, and a stiff bristle brush is often effective. GSA's procedure also lists an alkaline detergent. Rinse with as little water as practical and blot.
4. Stop before it is perfectThe GSA procedure advises stopping at roughly 85 percent clean, because most damage happens while chasing the last of a stain.

Things to avoid on brick, all from the BIA note: unbuffered muriatic acid, wire brushes and high-pressure water. Do not mix cleaning products. Painted brick, natural stone and historic masonry each need their own approach; for older houses, see chimneys on historic homes.

Use the clean brick as a test

Once the face is clean, it becomes a gauge. Burn the way you normally do and look at the brick after each fire. A faint haze after a lighting puff is useful information; a dark line that returns within a few fires means the spill is regular and the cause is still there.

That is the point to have the system looked at. When we assess a fireplace that stains, we check that the damper opens fully, look at the smoke chamber and smoke shelf, send a camera through the flue if its shape permits, and look at the cap and chimney top from the roof if conditions allow. Your notes and the before-and-after photos of the stain are worth sharing. You see our findings, photographed, before any repair is booked. Our fireplace repair page covers smoking fireplaces specifically.

When a stain means stop using the fireplace

Stop burning and arrange an inspection if:

• A gas log set, gas fireplace or insert is leaving soot on the face, louvers or glass.
• Soot appears along cracks in the brick or mortar above the opening, instead of rising from under the lintel. Smoke coming through the masonry is a different and more serious problem.
• The lintel is sagging, rusted through or pushing the brick above it out of line.
• Dark staining shows up on walls or ceilings away from the fireplace; see stains on walls and ceilings near the chimney.
• You have noticed loud roaring, popping or puffy flakes of creosote, which can follow a chimney fire; see signs you've had a chimney fire.

Questions homeowners ask

Sources

1. Chimney Safety Institute of America (CSIA), Frequently Asked Questions
2. Brick Industry Association, Technical Note 19: Residential Fireplace Design
3. Brick Industry Association, Technical Note 20: Cleaning Brickwork
4. U.S. General Services Administration, Removing Smoke Stains From Brick Masonry
5. Mason-Lite (Masonry Fireplace Industries), Virginiana vented gas log standard burner manual
6. U.S. EPA Burn Wise, Best Wood-Burning Practices

This guide is general information. It can't diagnose a specific chimney; an inspection can.