When using horizontal ducts to introduce outdoor air into an unconfined space, what is the free area requirement?

The correct answer relates to the standard practice for introducing outdoor air into an unconfined space, with specific free area requirements to ensure proper ventilation and combustion air. When calculating the necessary free area for horizontal ducts, it is established that there should be 1 square inch of free area for every 2,000 BTU/hour of input. This ratio is important because it ensures that there is sufficient outside air available for appliances to operate efficiently and safely.

This requirement helps to prevent negative pressure situations that could lead to improper combustion and energy efficiency losses. Proper ventilation also protects against the buildup of harmful gases, maintaining a safe environment. By meeting this guideline, one can ensure that the heating system operates optimally while complying with safety standards.