Fan airflow pressures are usually measured in...

• A. Inches of water column
• B. Pounds per square inch
• C. Pascal
• D. Millimeters of mercury

Answer: (A)

Fan airflow pressures are typically small, and inches of water column directly express how much pressure is needed to raise a column of water by one inch. This makes it a practical, intuitive unit for measuring static pressure in ducts, across filters, and through coils, which is why it’s the standard in HVAC and ESCO-style testing. Other units pack too much magnitude or belong to different contexts: pounds per square inch is a larger unit better suited for overall system or refrigerant pressures, pascals are the SI standard but aren’t the commonly used reference in this field, and millimeters of mercury is used for vacuum-related pressures rather than typical airflow in ducts.