What must be the size of the openings when horizontal ducts are used to introduce air into a confined space?

The correct choice specifies that the size of the openings when horizontal ducts are used to introduce air into a confined space must be 1 square inch for every 2,000 Btu/h of input. This standard is based on guidelines established in building and safety codes, which take into account factors such as adequate air supply, ventilation requirements, and safety considerations for combustion equipment.

Sizing the openings appropriately is critical for ensuring that there is sufficient airflow to support combustion processes and to prevent hazardous conditions such as carbon monoxide buildup. If the openings are too small, the system could become starved for air, leading to inefficient operation and potential safety risks. Having a calibrated opening size related to the Btu inputs helps ensure that there is a balance between the gas input and the required air for combustion.

Understanding these requirements is vital for installers and technicians, as improper sizing can lead to system failures and dangerous conditions. This guideline reflects a nuanced understanding of HVAC principles, making it important for anyone working with gas-fueled appliances or heating systems to adhere closely to these specifications.