Chimney Fires in Boston, MA: Causes, Warning Signs, and Prevention
A chimney fire can crack the liner and reach the framing in minutes. Here is what causes them, how to recognize one, and the steps that keep a Boston chimney from ever having one.
How a chimney fire starts
A chimney fire happens when the creosote built up inside the flue ignites, and once you understand that, the causes and the prevention both become clear. Creosote, the tarry residue that wood smoke deposits on the chimney walls, is combustible, and when enough of it has accumulated, the heat of a hot fire below can set it alight. Sometimes the trigger is an overfired stove or fireplace, burning too hot and sending a surge of heat up the flue. Sometimes it is a stray ember or a burst of sparks reaching the glazed creosote higher up. Either way, the fuel for a chimney fire is the creosote, and the amount of creosote is what determines whether a chimney is at risk.
Some chimney fires are dramatic and unmistakable, with a loud roaring like a freight train, dense smoke and sparks shooting from the top of the chimney, and a glowing flue. Others, and this surprises people, burn slow and quiet, smoldering inside the flue without the noise, sometimes without anyone in the house realizing it is happening. The slow ones are dangerous precisely because they go unnoticed. They can reach temperatures high enough to crack the clay-tile liner and damage the chimney even when no one saw flames, leaving the chimney compromised and far more dangerous to use the next time, with the homeowner none the wiser.
The damage a chimney fire leaves behind
The immediate danger of a chimney fire is the obvious one, that the fire can spread from the flue to the house. But the lasting danger is what a chimney fire does to the liner, because that damage turns a one-time event into an ongoing hazard. The intense heat of a chimney fire, often well above what the flue is built to handle, cracks and can even shatter the clay tile that lines the chimney. That liner is the barrier that keeps the heat and gases of every future fire away from the wood framing packed around the flue, and once it is cracked, that barrier is breached.
This is why a chimney that has had a fire, even a small or unnoticed one, must be inspected before it is used again. A camera scan up the flue will reveal whether the liner has cracked, and if it has, the chimney is no longer safe to burn in until it is relined, because the next ordinary fire now has a path for its heat to reach the structure. Many homeowners do not realize their chimney has had a slow, quiet fire until an inspection turns up the telltale damage, puffy or honeycombed creosote, cracked tiles, warped metal components, and discoloration. Finding that evidence is one of the most important things a chimney inspection does.
- Cracked or shattered clay-tile liner from extreme heat
- A breached barrier between the flue and the wood framing
- Warped or discolored metal damper and connector parts
- Puffy, honeycombed creosote that signals a past fire
- A chimney that is unsafe to use until it is inspected and relined
Preventing a chimney fire in a Boston home
Because a chimney fire is fueled by creosote, preventing one comes down to keeping the creosote in check and burning in a way that produces less of it. The foundation is the yearly sweep, which removes the buildup before it reaches a dangerous level, and the yearly inspection that goes with it, which catches a cracked liner or a sluggish draft that would otherwise let creosote accumulate faster. In Boston's long heating season, that annual maintenance is not a luxury, it is the single most effective thing a homeowner can do to keep a chimney fire from ever starting.
How you burn matters too, and a few habits make a real difference. Burn only well-seasoned, dry hardwood, never wet or green wood, because damp wood burns cool and smoky and lays down far more creosote. Never burn trash, cardboard, or treated wood, which produce heavy residue and can flare unpredictably. Build hot, clean fires rather than damping a fire down to smolder overnight, since a slow, oxygen-starved fire is exactly the condition that produces the most creosote. And keep the chimney capped, so the flue stays dry and drafts well. None of these replace the yearly sweep, but together with it they keep a Boston chimney burning safely.
What to do if you suspect a chimney fire
If you ever suspect an active chimney fire, the loud roaring, the sparks and dense smoke from the top, the intense sound from the flue, treat it as the emergency it is. Get everyone out of the house and call the fire department. A chimney fire can spread to the structure quickly, and it is not something to fight yourself. Do not assume that because a chimney fire seems to have burned itself out the danger has passed, because the heat may have already cracked the liner and the chimney may have spread fire into concealed spaces in the structure.
After any chimney fire, suspected or confirmed, do not use the chimney again until it has been professionally inspected. The fire may have damaged the liner in ways that are invisible from the firebox but plainly visible to a camera, and using a chimney with a cracked liner risks a far worse fire next time. Have the flue scanned, find out exactly what the fire did, and reline if the inspection shows the liner is compromised. The whole point of the inspection after a fire is to make sure the chimney is genuinely safe before another match is struck, rather than gambling that the damage was minor.
The surest defense against a chimney fire is the boring one, a yearly sweep and inspection that keeps the creosote down and catches a problem early. If your Boston chimney is overdue, or you suspect it has had a fire, call us for an inspection and a camera scan before you burn again. Call 508-296-8030.
When it is time, reach us at 508-296-8030 and a real person will pick up.