Every building needs to stay comfortable. Too little cooling capacity and occupants swelter in July. Too much and the owner pays for oversized equipment that cycles on and off inefficiently, wasting energy and money. HVAC load calculations are how you figure out the right size.

On the PDD exam, you need to determine the size of mechanical systems and components. That means understanding two types of heat loads (sensible and latent), knowing how airflow measured in CFM connects to capacity measured in BTU/h or tons, and applying standard formulas to size equipment for a given scenario.

The calculations themselves follow ASHRAE-standardized methods. Sensible loads come from conduction through walls, solar gain through glass, lighting, equipment, and people. Latent loads come from moisture: occupants breathing and perspiring, infiltration of humid outdoor air, and any process moisture sources. Both must be accounted for when sizing equipment.

Architects don't typically perform full Manual J or block load calculations on their own. But you do need to understand the inputs, check the outputs, and coordinate with mechanical engineers. When a consultant hands you a schedule showing a 15-ton rooftop unit, you should be able to verify whether that makes sense for a 5,000-square-foot office with a large west-facing curtain wall. That capacity check is exactly what NCARB expects you to handle.