What is connected to the 48" x 104" vertical duct near grid line intersection H5?

The choice indicating that the outside air intake to air handler 3 is connected to the 48" x 104" vertical duct near grid line intersection H5 is correct because this particular duct indicates the pathway for outside air. In HVAC systems, outside air intakes are crucial for maintaining indoor air quality and ensuring that air handling units receive the requisite fresh air supply.

In the context given, identifying it as an outside air intake suggests that this duct is intended to bring in fresh air from the outside, which is then conditioned and distributed throughout the space by air handler 3. Often, these designs specify the size and route of ducts to optimize air flow and ensure efficiency in the overall heating, ventilation, and air conditioning process.

The other choices address alternative functions of ductwork, but they do not align with the identified purpose of the vertical duct at grid line H5. For instance, return air from the basement or supply air to the basement would imply a different function and routing involving movement of air within the system rather than directly bringing in air from outside. Exhaust air from Room 018 also suggests a different ducting purpose altogether, as it indicates air being expelled from a space, not brought in from outside. Thus, the specific designation of this vertical