A chimney vent is the part of a chimney which provides an outlet for the hot gases which are carried up the chimney. Many regions of the world have specific laws about how chimneys should be vented which are designed to address concerns about fire safety and pollution. There are also some specific design considerations which have to be taken into account when making or installing a chimney vent, as a poorly designed vent can cause gases to build up inside the chimney, which is very undesirable.
Chimneys are used to transport the byproducts of combustion away from the area where they are generated. When things like coal, wood, and gas are burned to generate energy or heat, they create flue gases, which include a mixture of gases and particulate matter. These flue gases can be harmful to inhale and if they are allowed to build up they may suppress the fire, so they need to be vented away from the area where they are produced, and this is where a chimney comes in.
The body of the chimney, known as the flue, is designed at a height and width which is intended to create draft, a gentle pull which draws the flue gases up the chimney and away from their source. The chimney vent provides an outlet, releasing the gases safely into the surrounding air. Many regions require that chimney vents have filters to trap particulates, and some also include traps for certain flue gases. The chimney vent must also have a cap so that water cannot enter the flue, and it may need a spark arrestor to prevent stray sparks from drifting out of the chimney and starting a fire.
Maintaining a chimney system in good working order is critical for efficiency and safety. If a chimney is allowed to become clogged, it may not be able to vent gases as effectively. Buildups can also become a fire hazard. The chimney vent requires periodic inspection to confirm that filters are still in place and do not need to be replaced or cleaned.
Historically, chimneys were designed to vent straight up into the air, and some were quite long. Some chimney systems now vent out sideways, or may vent gases through a series of bends, depending on the design. For certain applications, such as dryers and small gas heaters, it may only be necessary to have a very short vent to the outside which prevents gases from building up indoors.