Chimneys are natural sources of drafts because they are gaping holes that emit and pull in air. Anyone who owns a wood burning appliance should understand the concept of draft. Air moving up a chimney follows the same physical principles as does water flowing in a hose. Addressing chimney draft issues enables the fireplace and chimney to operate in peak condition.
When the fireplace chimney is filled with hot air, additional air is pulled through the firebox in a process called draft. A chimney is an example of a negative pressure system because air pressure is negative. Increasing the chimney draft is similar to opening a water faucet connected to a hose. By burning a fire hotter, lighter air is created, increasing the draft in the chimney through increased pull. Increasing the chimney height will also provide more draft.
Given the same amount of draft, a flue that is larger will exhaust more smoke from a fireplace. However, just as a water hose may become plugged, chimney airflow may be restricted by several conditions, slowing the flow of smoke up the chimney. A closed or improperly operating damper, excessive deposits of creosote, or dirty chimney cap can create poor air flow within a chimney.
An improperly constructed chimney or structural damage to the area can also prevent the maximum amount of smoke from being exhausted from the fireplace. In some cases, smoke may be emitted backwards, ending up in the home. This forces occupants to breathe the contained chemicals and impurities, which is a health hazard.
A chimney sweep can inspect the chimney to identify whether the proper amount of draft and air flow are occurring. If creosote has built up or something is obstructing the air flow, the sweep will remove it by cleaning the chimney. Structural issues can be addressed by chimney repair or in the most severe cases, replacement.