Ventilation (architecture)

Ventilation is the intentional introduction of outdoor air into a space, primarily to control indoor air quality by diluting and displacing indoor pollutants. It can also influence indoor temperature, humidity, and air movement, affecting thermal comfort and building energy use. Ventilation is important where combustion occurs indoors, as fireplaces, heaters, and other combustion sources consume oxygen and produce gases, smoke, and water vapor that may need to be removed. Ventilation is commonly classified as natural ventilation, mechanical ventilation, or mixed-mode ventilation. Natural ventilation relies on passive forces such as wind pressure and the stack effect, while mechanical ventilation uses fans to move outdoor air into or out of a building. Mixed-mode systems combine natural and mechanical processes. Ventilation design considers both the amount and distribution of airflow. Ventilation rates may be expressed as volumetric flow, as airflow per person or unit of floor area, or as air changes per hour (ACH). Airflow distribution affects ventilation effectiveness, while required ventilation rates can depend on occupancy and pollutant sources. Natural ventilation can reduce the risk of airborne disease transmission. If outdoor air is polluted, introducing it without adequate treatment can worsen indoor air quality. Demand-controlled and smart ventilation systems can adjust ventilation rates according to occupancy or environmental conditions to balance indoor air quality and energy use. Ventilation rates are addressed by building codes and standards, including ASHRAE Standards 62.1 and 62.2. Passive ventilation techniques have been used since antiquity, while mechanically driven systems have been developed from the 18th century; modern ventilation-rate standards began to emerge in the 19th century.