When sourcing duct blower fans, the most critical metric is Air Volume (CFM/m³/h) and Static Pressure, which determines the fan's ability to push air through resistance like filters or long ducting. You must verify the Motor Type, prioritizing EC (Electronically Commutated) motors for energy efficiency and precise speed control over traditional AC motors. Additionally, check the Noise Level (dB) to ensure it meets workplace safety or residential standards, and confirm the Housing Material (e.g., flame-retardant ABS plastic or galvanized steel) matches the environmental conditions of the installation site.