Chimneys are structures designed to ventilate hot smoke or fumes from boilers, stoves, ovens, or fireplaces. They are typically vertical, or as close to vertical as possible, to ensure smooth gas flow and to allow air to be drawn in, creating the so-called chimney draft or chimney effect. The space inside the chimney is called the flue. Chimneys can be found in buildings, steam locomotives, and ships.

The height of the chimney affects its ability to transport flue gases to the external environment due to the chimney effect. Additionally, using chimneys in high-altitude areas can reduce the impact of pollutants on the surrounding environment. Dispersing pollutants over a larger area can lower their concentration and promote compliance with regulatory limits.