What is the minimum required dimension for a horizontal duct used to introduce combustion air into a confined space?

The minimum required dimension for a horizontal duct used to introduce combustion air into a confined space is set at 3 inches. This dimension is crucial because it ensures a sufficient airflow capacity that allows for adequate combustion in appliances that require outside air for proper operation.

A duct that is too narrow may not provide enough air intake, which could lead to insufficient combustion air, ultimately causing poor appliance performance or even safety concerns due to the buildup of combustion gases. The 3-inch minimum ensures efficient and safe air flow while accommodating various types of heating appliances designed to operate in confined spaces.

When considering installations according to safety codes and manufacturer specifications, adhering to this minimum dimension helps ensure compliance and promotes efficient heating system operation.