HVAC CFM Calculator
Determines required airflow in cubic feet per minute for any room based on size and ventilation needs
Length of the room in feet
Width of the room in feet
Height of the ceiling in feet
How many times the air volume is replaced per hour
Enter room dimensions to calculate volume
Cubic feet per minute of airflow needed
Duct diameter at 900 FPM standard velocity
Frequently Asked Questions
What is CFM in HVAC?
CFM stands for cubic feet per minute and measures the volume of air flowing through a duct or system. It determines how quickly air is delivered to and removed from a room. Proper CFM ensures adequate ventilation, comfort, and air quality.
How many CFM do I need per room?
It depends on room volume and required air changes per hour (ACH). Offices typically need 4-6 ACH, kitchens need 7-8, and bathrooms need 6-8. Multiply room volume by ACH and divide by 60 to get the required CFM.
What are air changes per hour (ACH)?
ACH is the number of times the total air volume in a room is completely replaced in one hour. Higher ACH means more ventilation. Residential living spaces typically need 4-6 ACH, while commercial kitchens or labs may need 12-15 ACH for proper air quality.
How do I size ductwork for a given CFM?
Duct size depends on the required CFM and the desired air velocity (typically 600-900 FPM for residential). A 6-inch round duct handles about 100 CFM, an 8-inch handles about 160 CFM, and a 10-inch handles about 275 CFM at standard velocities.
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