An essential part of both indoor and outdoor fireplaces, are fireplace chimneys, they vent the hazardous and noxious gases, produced by the combustion of fuels, safely to the outside atmosphere. Fireplace chimneys regulate the flow of air and keep excessive heat from combustible materials that surround the fireplace.
Initially, fireplace chimneys were made of brick and mortar, bordered with fireproof tiles. But the newer models of metal are easy to install. Fireplace chimneys must be able to withstand the recurrent heating and cooling process of the fireplace and also the corrosive compounds produced after combustion.
The flue, containing the products of combustion, forms the inner and the most important layer of fireplace chimneys. In the case of wood burning fireplaces, a highly flammable substance called creosote is deposited on the flues, which blocks the passage of air through the system. A clean flue is crucial for the unhindered dispersal of combustion products.
Apart from flues, fireplace chimneys include chimney caps, chimney flashing, chimney dampers, chimney liners, and cleanout doors. Chimney caps usually made of copper, stainless steel or black steel act as the chimney cover that prevent downdrafts and protect the chimney against rain and animal invasions. Chimney Dampers close the fireplace chimneys when they are not in use, whereas the Chimney flashing provides waterproofing to the chimneys. Stainless Steel, cast-in place (a thick layer of cement-like material), and terracotta chimney liners create a smooth path for drafting and improve the performance of fireplace chimneys. The cleanout doors are metal doors, found at the base of the fireplace chimneys, which facilitate easy cleaning of ash pit.
The design and size of fireplace chimneys can affect the performance of fireplaces. A good diameter and height is needed for the proper combustion of fuels. Further, the fireplace chimneys must be tall enough to allow a smooth airflow.
In order to avoid the risk of chimney fires, the fireplace chimneys must be cleaned at least once in a year. This will also prevent carbon monoxide poisoning.