What is a flue?
A flue is the internal passage or duct inside a chimney through which smoke, gases, and heat from a fireplace, furnace, or water heater travel upward and out of the home.
The flue is the open channel that runs up the interior of a chimney, carrying smoke and combustion gases from your fireplace, wood stove, furnace, or water heater to the outside air. It forms the core pathway that allows heated gases to rise and exit safely rather than backing up into living spaces.
Connecticut homes often have either a single flue or multiple flues within the same chimney structure. A single flue typically serves one appliance, while a multi-flue chimney (sometimes called a multi-stage or multi-liner setup) keeps separate appliances isolated from each other. This separation prevents gases from one heating source from entering another appliance's vent or back-drafting into the home. For example, a two-flue chimney might accommodate both a fireplace and a furnace, each with its own dedicated passage.
Flues require regular inspection and cleaning to function properly. Creosote buildup, debris, or structural damage can restrict airflow, reduce heating efficiency, or create dangerous conditions. When hiring chimney masonry professionals, part of their assessment involves checking flue condition, size, and whether your current setup matches your home's heating needs.