Air Conditioning Repair Certification (ETI) Practice Exam

Fan airflow pressures are typically measured in inches of water column (WC). This measurement is specifically suited for low-pressure applications, such as those found in HVAC systems. The use of inches of water column allows technicians to assess the static pressure in duct systems, which is essential for determining the efficiency of airflow and ensuring the system operates within the designed parameters.

Inches of water column is a more appropriate unit for measuring the relatively small pressures encountered in air handling systems, as it is designed to convey the subtle differences in pressure that can significantly impact the performance of heating and cooling equipment.

The other units mentioned would not be suitable for this application. Inches of mercury (Hg) is typically used for measuring atmospheric pressure in barometric contexts. Pascals (Pa) are often used in scientific applications and can express pressure but are not commonly employed in HVAC practices for airflow measurement. Pounds per square inch (PSI) measures higher pressures, typically related to gases and liquids under pressure in different contexts, making it unsuitable for low-pressure airflow applications.