For combustion air taken from outdoors, what is the free area requirement for ventilation air from inside the building?

The correct requirement for ventilation air from inside the building when combustion air is taken from outdoors is based on specific criteria set to ensure proper combustion and a safe environment. The standard of 1 square inch of free area for every 5,000 BTU represents a balance between providing sufficient oxygen for combustion and maintaining control of airflow within the building.

This standard ensures that there is enough ventilation to support the safe operation of heating appliances while minimizing potential heat loss and drafts. When setting this requirement, the intention is to prevent a situation where the combustion appliance can create a negative pressure in the building that could lead to backdrafting, which is a safety hazard.

By adhering to this ratio, it allows for an adequate exchange of air, ensuring that combustion can take place efficiently while also safeguarding against excess moisture or the buildup of harmful gases. Therefore, the specified area is a critical safety guideline that reflects industry practices for the installation and operation of combustion appliances within structures.