Windbox is a technical term that refers to the area in a furnace where air is introduced to support combustion. Although there are no one-word synonyms for windbox, some phrases that are commonly used in the field of furnace engineering include combustion air chamber, air plenum, and air inlet duct. Other related terms include air distribution system, combustion chamber, and air supply unit. In general, any synonym for windbox will likely focus on the function of the area, which is to provide a controlled flow of air to support the combustion process in a furnace.