Define CFM and explain how it relates to duct sizing and air distribution.

Define CFM and explain how it relates to duct sizing and air distribution.

• A. Cubic feet per minute; measures the rate of air delivery and is used to size ducts and achieve target room ventilation and comfort.
• B. Cooling flow management
• C. Cooled airflow per minute
• D. Central fan motor frequency.

Answer: (A)

CFM stands for cubic feet per minute, the rate at which the HVAC system delivers air. This airflow value is the basis for duct sizing and air distribution because ducts must carry a defined amount of air without excessive noise or pressure loss. The key relationship is CFM = velocity × area. That means for a given CFM, increasing the duct cross-sectional area lowers air velocity, while using a smaller duct raises velocity and can cause more friction and noise. Designers pick target CFM to meet cooling/heating loads and ventilation needs, then size the ducts so the air can be moved at a comfortable, efficient velocity. This also ties to distributing air between spaces so each room gets its intended CFM, and to calculating air changes per hour by relating CFM to room volume.

CFM stands for cubic feet per minute, the rate at which the HVAC system delivers air. This airflow value is the basis for duct sizing and air distribution because ducts must carry a defined amount of air without excessive noise or pressure loss. The key relationship is CFM = velocity × area. That means for a given CFM, increasing the duct cross-sectional area lowers air velocity, while using a smaller duct raises velocity and can cause more friction and noise. Designers pick target CFM to meet cooling/heating loads and ventilation needs, then size the ducts so the air can be moved at a comfortable, efficient velocity. This also ties to distributing air between spaces so each room gets its intended CFM, and to calculating air changes per hour by relating CFM to room volume.