What is the minimum area required for each duct opening in a confined space with a 150,000 BTU residential furnace?

The minimum area required for each duct opening in a confined space with a 150,000 BTU residential furnace is determined by the need to provide adequate combustion air and ventilation. In most residential furnace installations, there are guidelines that specify the amount of duct area necessary based on the input BTU ratings of the furnace. For a furnace with an input of 150,000 BTUs, building codes and industry standards indicate that at least 75 square inches of duct opening is necessary. This allows for proper airflow, ensuring the furnace operates efficiently and safely.

Adequate duct sizing is crucial, as insufficient duct area can lead to combustion issues or insufficient heating, potentially causing the furnace to operate improperly or even create hazardous conditions. Therefore, having a minimum of 75 square inches ensures a sufficient air supply for the furnace's operation, making this the correct choice.