Francis D. K. Ching  characterizes a chimney as an “incombustible vertical structure, which contains a duct through which smoke and gases from a fire or furnace are pushed outwards and through which an air current is created.” While its pipes can be hidden in walls or other structures, the chimney top usually remains prominent in order to transfer dangerous gases from the inside out without dirtying the interior or harming the health of the occupants. Being vertical elements, there are chimneys that become major landmarks in the urban landscape, especially in industrial projects. At the time of drawing, deciding on the “weight” that the chimney will have in a project is essential. At Casa Milá, for example, Gaudí crowns the building in sinuous and curvy sculptural chimneys. In other cases, the solemnity of the building aesthetic is mirrored in its chimney, whereas in others, the architects render the chimney as hidden as possible. Recently, too, many chimneys have been refurbished for new uses or to accommodate new cleaner technologies. Whether it takes a prominent role or is hidden from view, see below some chimney design tips and possibilities of use.
Building an efficient chimney is not a simple task. In addition to having to be well dimensioned to drain the smoke properly, one must take into account the surrounding context, such as wind, nearby structures, or building height limits. In theory, the operation is simple. As the gases inside the chimneys are much hotter than the outside air, they are also much less dense. This creates a pressure difference inside the chimney, where the denser part stays lower and the lighter part rises higher, forming a natural flow of air. If a chimney is too long, it may be that the gases cool down before reaching the top, and eventually return to the source. For these and other reasons, designing chimneys requires a mixture of technical and empirical knowledge, and it is always prudent to consult someone with experience in this type of project or work.
In general, the chimney top must be at least 50 centimeters higher than the roof. There are local regulations that determine minimum heights so that the smoke does not disturb neighboring buildings. The less complex the chimney shaft shape, the less chance of problems, and in general, the chimney should be 1/10 to 1/12 the size of the opening of the fireplace. In addition, dirt in the chimney can greatly interfere with its performance, so periodic maintenance is essential.
There exist many design possibilities for creative chimneys. Large industrial chimneys attract attention as urban landmarks. In the Campus De La Comunicació Poblenou project, by RQP Arquitectura, the iconic chimney of the site's former textile mill was conserved and brought back into operation in association with a neighboring power plant. The huge chimney of the Tate Modern Museum, in London, is one of the most striking features of the skyline along the River Thames. In a project for a bakery in Pozoamargo, a large chimney stands at the top of the roof, a unique element that reminds us of the industrial character of the building. Inside, the chimney becomes a “well of light” over the wood oven. In the ARCH 4 F-house, the chimney is highlighted as a prominent vertical element, using the same material as the building's foundation. And in TW Ryan Architecture's Three Chimney House project, the three vertical chimneys break the horizontality of the design. Finally, in a Japanese project by Nadamoto Yukiko Architects, the solemn language of the house is augmented by its chimney closely adhering to the aesthetics of the rest of the project.
However, due to concerns about pollution and safety (due to the possibility of carbon monoxide poisoning), there are some places that have outright banned wood-burning fireplaces. In addition, with the deindustrialization of many countries and the obsolescence of most industrial chimneys, many remain as large inactive monuments or are reused for new uses. The structures can remain intact, be preserved, or even serve artistic transformations or other uses.
But on the domestic scale, fire continues to fascinate human beings. While wood burning fireplaces have been banned in some places, gas, bioethanol, and pellet fireplaces have gained a lot of prominence, reducing smoke and much of the pollution associated with wood fireplaces. A widely used alternative is the pellet, which utilizes of small cylinders of dry sawdust. Likewise, the bioethanol option does not emit smoke, eliminating the need for chimneys. There are also electric fireplaces, which do not produce dirt or smells, but consume a high amount of electrical energy. In gas fireplaces, the flame is generated like in a stove, and the heat is spread into the environment by heating volcanic stones located at the base of the fireplace.
Evidently, when working with fire, architects must take a lot of care to ensure safety and fulfill important requirements. Whether in an oven, a barbecue, a fireplace, or an industrial furnace, it is vital that all regulations are observed and that the chimneys are considered from the design stage, so they do not become an unpleasant annex to the already constructed building.
See, in this folder, a series of possibilities in the use of chimneys in architecture.