What factor does NOT directly affect HVAC system sizing?

Local air quality is not a direct factor in determining the size of an HVAC system. The primary considerations for HVAC system sizing include aspects like building layout, climate conditions, and square footage, all of which directly influence the heating and cooling loads that the system must meet.

Building layout affects how air circulates within the space and how effectively the system can maintain temperature throughout the different areas. Climate conditions play a critical role since the HVAC system needs to account for temperature extremes and humidity, ensuring it can adequately manage internal comfort throughout the year. Square footage is essential as it determines the volume of space that requires heating or cooling; larger areas typically require more capacity to maintain desired conditions.

While local air quality can inform decisions about filtration and ventilation needs, it does not influence the physical sizing of the HVAC equipment itself. Thus, focusing on the factors that directly affect system performance and capacity helps in appropriately sizing an HVAC system for any given structure.