Chimney 101: get to know your smokestack

Photo by Heidi Murphy / Shutterstock

Chimney 101: get to know your smokestack is one of our three-part series about chimney maintenance, along with:
The essential guide to cottage chimney maintenance
Worried about creosote? Here’s what to look for

Ready to learn more about how a chimney works? Welcome to Chimney 101.

A chimney’s key attribute is “draft”—its ability to pull air from the stove or fireplace up and out of the cottage. This natural flow through a bed of coals, for example, makes it easier to kindle fires and helps the blaze reach efficient combustion temperature. As a bonus, draft increases as the fire grows. “The greater the temperature difference between the exhaust gases in the chimney and the outside air, the stronger the draft,”says John Gulland, one of the originators of Canada’s Wood Energy Technical Training (WETT) certification program. Likewise, “the taller the chimney, the more draft it will produce.”

The most reliable draft comes from a straight, well-insulated interior chimney that emerges near the highest point of the roof. It’s an express lane for the fire’s heat and combustion gases: they stay hot and ascend quickly. This approach is most common with newer woodstoves and fireplace inserts. 

Almost any departure from this straight-up layout will slow the gases and potentially cause headaches. Every 90-degree elbow in the system causes turbulent airflow, allowing flue gases to bog down in transit. Exterior chimneys are cold, whether they’re brick or metal, making gases less buoyant. Chimneys that are too short or vent too close to a roof produce a draft that is weak or unreliable. The results include smoky downdrafts; smoke that spills from the stove when you open the door; and that dank, sooty odour when the fireplace isn’t in use. Worst of all, these layouts tend to accumulate more creosote, making maintenance a bigger concern.

Worried about creosote? Here’s what to look for

This article was originally published as part of”Up in Smoke” in the Fall 2021 issue of Cottage Life. Read the rest at The essential guide to cottage chimney maintenance.

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