Is It Normal for Sparks to Come Out of a Chimney?

Where sparks come from

A wood fire throws off light, burning bits of material, and the draft carries them up the flue. Most burn out within a few feet and never reach the top. The ones that make it out tend to come from fuel that burns fast and light, breaking apart into flakes that ride the hot gases up and out before they finish burning.

How far a spark travels depends on its size, how hot the fire is and how strong the draft is. A tall chimney on a cold night pulls hard, which is good for the fire but carries more sparks out with it. That is why the same fireplace can be spark-free on a mild evening and throw a shower of them on a frigid one.

• Newspaper, cardboard, junk mail or wrapping paper in the fire
• Dry pine needles, branches, or a holiday tree burned in the fireplace
• Softwood scraps and kindling that flare up quickly
• A very hot, roaring fire with a strong draft
• Burning creosote inside the flue, which is a chimney fire

Normal sparks and warning signs

A short burst of small sparks right after you light the fire, or when you add a handful of kindling, is one thing. Sparks that keep coming long after the fire is established, embers big enough to see glowing on the roof, flaming flakes drifting down into the yard, or a loud roar or rumble from the chimney are another. Those point to creosote burning inside the flue.

Other chimney fire signs include a strong hot smell, the chimney breast or stove pipe becoming very hot, dense dark smoke from the top, and popping or cracking sounds. A chimney fire can also burn quietly and only show later as flaky, puffed creosote and cracked tiles.

• A few sparks at lighting are paper or kindling burning off; that is normal, and less paper helps
• Sparks whenever softwood goes on are light fuel flaring up; switch to seasoned hardwood
• Steady sparks with dense smoke can mean creosote is burning; stop adding fuel and be ready to leave
• A roaring sound, flames or big embers at the top mean a chimney fire; get out and call 911

If you think it is a chimney fire

Get everyone outside and call 911. If it can be done safely on the way out, close the glass doors or a stove's air controls to starve the fire of air, but do not spend time on it and do not pour water into a hot firebox or flue. From outside, watch the roof and nearby roofs for embers, and tell the fire department if you see any.

After any chimney fire, the flue should be inspected before the fireplace is used again, as NFPA 211 calls for, because the heat can crack tiles and mortar and reach the framing around the chimney even when the fire seemed small.

Why sparks matter more in dense neighborhoods

In rowhouse blocks and closely built suburbs, roofs sit close together, and one chimney can be a few feet from a neighbor's roof, a deck or a pile of leaves in a gutter. A spark that would burn out harmlessly in an open field can land on a dry roof edge, a wooden fence or a porch cushion. Flat roofs with tar-based coatings and older asphalt shingles are the surfaces most worth protecting.

Wind matters too. Gusty nights during nor'easters and cold fronts carry embers further, which is a good reason to keep fires modest when the wind picks up.

What a spark arrestor does

A spark arrestor is a metal mesh screen around the sides of a chimney cap. Smoke and gases pass through it, but embers big enough to start a fire on a roof or in a yard are caught and burn out inside the cap. The same cap keeps out birds, squirrels and raccoons and keeps rain from falling straight down the flue, so one part solves several problems.

Caps come in single-flue models that fit over one flue tile and full-width models that cover the whole top of the chimney, including several flues at once. Stainless steel and copper outlast galvanized steel, which rusts through in a few seasons in our climate.

Getting the right screen

The mesh has to be the right size for the job. Openings that are too large let embers through. Openings that are too fine clog with soot and creosote, which chokes the draft and pushes smoke back into the room. The cap also has to sit high enough above the flue that smoke can leave freely, and it has to be sized to the flue it covers.

Whether a spark arrestor is required where you live depends on local code, and an appliance maker's installation instructions may set their own rules for the cap on that flue. Some gas appliance and stove instructions call for a specific listed cap, so check before fitting a generic one.

Keeping the screen working

On a wood-burning chimney, the screen collects soot and creosote over a season. A partly clogged screen slows the draft, which makes the fire smokier, which clogs the screen faster. The screen is checked and cleaned at each sweep, and a cap that is bent, rusted through or loose is replaced.

If the fireplace has started smoking into the room midseason for no obvious reason, a clogged cap screen is one of the first things to rule out.

Gas and oil flues do not throw sparks, but they still need their caps checked. Animals, leaves and rust flakes can block a boiler or water heater cap just as easily, and a blocked cap on a heating flue is a carbon monoxide risk rather than a fire risk. The same yearly visit should look at every cap on the chimney, not only the fireplace flue.

How to cut down on sparks

Burn split, dried hardwood instead of paper, trash or holiday greenery. Use only a little newspaper or a few fire starters to light the fire. Build moderate fires rather than packing the firebox. Keep the chimney swept so there is no creosote to catch. Make sure the cap and its screen are in place and in good shape: from the ground, look for a cap that is missing, bent, or rusted through on one side, and for a screen visibly packed with black deposits.