In more than forty years of sweeping Denver chimneys, I have stood in a lot of living rooms after a chimney fire. Nobody in those rooms ever thought it would be their house. The frustrating part of my job is knowing that nearly every one of those fires was preventable, usually with nothing more exotic than a yearly appointment and a few good habits. So the week before serious burning season, let me lay out how these fires actually start and what keeps them from starting.
How a chimney fire begins
A chimney fire is creosote catching fire inside your flue. Creosote is the condensed residue of wood smoke, it coats the inside of every working chimney to some degree, and it is flammable. Give it enough buildup and enough heat, a roaring fire below, a stray spark, an overloaded firebox, and the deposits ignite. Now the fire is not in your fireplace anymore. It is inside the structure of your house, burning at temperatures the flue may not be built to contain.
Some chimney fires announce themselves: a roar like a freight train, flames or dense smoke from the chimney top, a shuddering sound in the walls. Neighbors sometimes see them before the homeowner does. But many are quiet. They burn for a few minutes, run out of fuel or air, and go out on their own, leaving behind cracked flue tiles, warped metal, and a homeowner who has no idea it happened. That second kind worries me more, because a flue damaged by a quiet fire is compromised the next time you light up, and heat now has a path toward the framing of your house.
Signs you may have already had one
When we inspect chimneys, we find the fingerprints of past fires all the time: puffy or honeycombed creosote that looks like it boiled, cracked or missing tile sections, discolored caps, bits of creosote on the roof. If your damper is warped, your chimney has made noises you dismissed, or you once had a fire that seemed to breathe more fiercely than usual, say so at your next chimney inspection. Knowing what happened is the difference between a repair and a rebuild later.
Prevention, in order of importance
First, keep the fuel out of the flue. No creosote, no chimney fire; it is that direct. An annual chimney sweeping removes the year’s accumulation before it can matter. I went into the full story of how creosote builds and its three stages earlier this month, and the short version is that buildup you catch early brushes right out, while buildup you ignore hardens into something far more serious.
Second, burn like you mean it. Dry, seasoned wood and bright, hot fires produce the least creosote. Smoldering, damped-down overnight burns and green wood produce the most. If your habit is loading the box and choking the air down before bed, your flue is paying for that convenience.
Third, respect the size of your firebox. A fire built too large, or fed with wrapping paper, cardboard, or a dried-out Christmas tree branch, sends flames and torrents of sparks up a flue that was never meant to see them. The flue is a chimney, not an incinerator. Household trash never goes in a fireplace, period.
Fourth, keep the top of the chimney honest. A proper chimney cap with a spark screen keeps embers in and nesting material out. A nest sitting on your smoke shelf is kindling stored inside your chimney, which is about as bad an idea as it sounds.
Fifth, handle ashes like they are alive, because they often are. Coals buried in an ash bed can stay hot for days, far longer than anyone expects. Ashes go into a metal container with a metal lid, the container goes outside on a non-combustible surface well away from the house and the deck, and it stays there for several days before the ashes go anywhere else. Every winter, houses burn down over a paper bag of ashes set in the garage for just a minute. Do not be that story.
And keep the area around the hearth honest: the mantel decorations, the basket of newspapers, the dog bed that migrated toward the warmth. An open fireplace throws sparks, and a spark only needs one lucky landing. A proper screen in front of an open fire is cheap insurance that works every single evening.
If a chimney fire starts
Get everyone out of the house and call 911 from outside. That is the whole plan, and it is not negotiable. If it is safe to do so on your way, close the fireplace doors or the damper and shut any air controls, because starving the fire of air can slow it. But nothing about a chimney fire is worth staying inside for, and even a fire that seems to die on its own needs the fire department’s eyes and, afterward, a full inspection before you ever light another match in that fireplace. Chimneys can hold heat in hidden places for hours.
Afterward, the chimney is guilty until proven innocent. A fire hot enough to ignite creosote is hot enough to crack tiles and open joints you cannot see from the hearth, so the system gets a thorough top-to-bottom inspection, including a look inside the flue, before it carries another fire. Insurance companies generally want that documentation too, which is one more reason to have it done properly rather than eyeballed.
The appointment that makes this whole article boring
Here is what I want for you: a chimney fire should be something you only ever read about. A yearly sweep and inspection, dry wood, hot fires, a capped chimney, and nothing in the firebox that does not belong there. Do those things and the odds move overwhelmingly in your favor. We have been keeping metro Denver and Boulder chimneys safe since 1982, there is a certified technician on every truck, and the calendar between now and the holidays fills quickly. Call 303-973-7376 and let’s make sure your fireplace stays the best seat in the house.
Jon Geypens
Owner, Chimney Sweeps Of America
303-973-7376
