Resistance to air flow (static pressure) in an electric heater is measured in which unit?

The measurement of resistance to airflow, or static pressure, in an electric heater is commonly expressed in inches of water column. This unit provides a practical way to quantify the pressure exerted by the air within a duct or heating system.

Inches of water column is particularly suitable for HVAC applications because it reflects the small pressure differences encountered in heating and cooling systems. This unit allows technicians to easily assess the efficiency of airflow through the system, ensuring optimal performance.

While other units like PSI (pounds per square inch), inches of mercury, and Pascal are used for measuring pressure in different contexts, they are not typically employed for measuring static pressure within air handling systems. For instance, PSI is more appropriate for liquid pressure in plumbing systems, inches of mercury is often used in barometric pressure measurement, and Pascal is a metric unit commonly applied in industrial contexts. Thus, inches of water column remains the standard for evaluating the static pressure in HVAC systems, making it the correct choice for this question.