Where must a vertical duct terminate when introducing combustion air into a confined space?

The requirement for a vertical duct that is introducing combustion air into a confined space is based on ensuring that the air being supplied is not contaminated by other factors within the space. Terminating the duct 1 foot above the floor allows for several advantages. It helps to avoid any possible accumulation of harmful gases or products of combustion that could be present at the floor level, where heavier-than-air gases might settle. Additionally, this height facilitates better mixing of the incoming combustion air with the air already present in the confined space, supporting efficient combustion processes.

The choice of terminating at this height also aligns with safety standards and codes that mandate maintaining a safe distance from elements that could impact air quality and performance. By maintaining a distance of 1 foot from the floor, the system promotes a healthy airflow dynamic, reducing the risk of creating a negative pressure environment or pulling in potentially harmful gases.

Other options, such as terminating at ground level, 15 feet above the floor, or at ceiling level, either do not effectively address the need for clean combustion air or potentially expose the system to conditions that could disrupt its function. Thus, the ideal termination point is set at 1 foot above the floor to ensure optimal performance and safety.