Why a Boston, MA Chimney Needs a Sweep Every Year
Boston's long winters mean heavy chimney use, and heavy use means creosote. Here is what creosote actually is, why it causes chimney fires, and why a yearly sweep is the cheapest safety measure a Boston homeowner can take.
What creosote is and where it comes from
Creosote is the residue that wood smoke leaves behind on the inside of a chimney, and understanding what it is makes clear why it is so dangerous. When wood burns, it never burns completely, especially in the cooler, slower fires that an older Boston flue tends to produce, and the smoke carries unburned particles and gases up the chimney. As that smoke rises and cools against the chimney walls, those particles condense and stick, building a layer on the inside of the flue. In its earliest form it is a light, sooty powder, but as it accumulates and bakes through a season of fires it hardens into a thick, tarry glaze that bonds to the flue tile and is genuinely difficult to remove.
The reason this matters is simple and serious. Creosote is fuel. It is, in effect, concentrated combustible material lining the very passage that carries a fire's heat and sparks, and once there is enough of it, the conditions inside a working chimney can set it alight. A chimney fire is not a small thing. It burns at extreme temperatures, it can roar audibly up the flue, and the heat is high enough to crack the clay-tile liner and, through a cracked liner, reach the wood framing built around the chimney. Many house fires that start at the chimney begin exactly this way, with a creosote buildup that a yearly sweep would have removed.
Why Boston builds creosote faster
Several things about heating a home in Boston work together to produce creosote faster than a milder climate would. The first is simply the length and severity of the winter. A New England heating season is long and cold, so a fireplace or wood stove in regular use sees a great many more fires here than it would in a place with a brief, mild winter, and every fire adds to the layer inside the flue. A chimney that might stay reasonably clean over a short season can finish a Boston winter heavily glazed.
The second factor is the chimneys themselves. So much of Boston's housing is old, with original clay-tile flues that often draft a little sluggishly, and a slow draft means the smoke moves up the chimney more slowly and cools more before it exits, which gives more of the smoke a chance to condense onto the walls as creosote. The third is fuel. Burning wood that is not fully seasoned and dry, which is easy to do when firewood has sat through a damp New England fall, produces far more smoke and far more creosote than a clean, hot fire from dry hardwood. A long season, an older slow-drafting flue, and the occasional load of less-than-perfect wood add up to a chimney that needs a sweep every year without fail.
The warning signs between sweeps
A yearly sweep is the rule, but it helps to know the signs that something is wrong in the meantime, because a chimney will often tell you it needs attention before its next scheduled cleaning. A fire that does not draw well, with smoke spilling back into the room instead of rising up the flue, is a common signal, and it can mean creosote or a blockage is narrowing the passage. A strong, tarry, smoky smell coming from the fireplace, especially in warm or humid weather when it is not in use, points to creosote buildup inside the flue. Dark, oily staining around the firebox opening is another sign.
Some signs point to more than a routine cleaning. A loud, rumbling or roaring sound from the chimney while a fire is burning, or seeing dense smoke or sparks pouring from the top of the chimney, can indicate an active chimney fire, and that is a call-the-fire-department emergency, not a wait-and-see one. After any suspected chimney fire, the flue should be inspected before it is used again, because the event may have cracked the liner even if the fire seemed to burn itself out. If you notice the everyday warning signs, do not wait for the calendar. Have the chimney swept and looked at, because the buildup that produces those signs is exactly what a sweep removes.
- Smoke spilling back into the room instead of drawing up
- A strong tarry or smoky smell from an unused fireplace
- Dark, oily staining around the firebox opening
- Visible creosote flakes or buildup at the firebox
- A roaring sound or heavy smoke from the chimney top, which can mean an active fire
What the yearly sweep actually buys you
Set against the cost of a chimney fire or a house fire, a yearly sweep is one of the least expensive and most worthwhile things a Boston homeowner does. Removing the creosote takes away the fuel that a chimney fire needs, which is the whole point, and the cleaning restores the draft so the fireplace or stove burns more cleanly and efficiently, which in turn lays down less creosote going forward. A clean flue is a safer flue and a better-burning one, and the difference is immediate the next time you light a fire.
The sweep also doubles as the moment your chimney gets looked at, which is its own value. A clean flue is the only flue you can really inspect, so the annual cleaning is the natural time to catch a cracked tile, an open mortar joint, a rusted damper, or the first signs of water working through the masonry, while each of those is still a small repair. A homeowner who keeps up with a yearly sweep and inspection rarely faces the kind of large, sudden chimney problem that catches up to a chimney left unattended for years. The habit is the protection.
If your Boston chimney has not been swept this year, or you are noticing any of the warning signs above, the next step is a sweep and an inspection, before the heating season hits its stride. We will clean the flue, tell you honestly what shape the chimney is in, and put any recommendation in writing with no pressure. Call 508-296-8030.
When it suits you, call 508-296-8030 and we will get a look at the chimney.