Air Changes Per Hour Calculator
Determines whether an HVAC system is cycling enough air for a given space volume
Length of the room in feet
Width of the room in feet
Height of the room from floor to ceiling in feet
Cubic feet per minute supplied by your HVAC system
Total volume of the room in cubic feet
Number of times the air in the room is fully replaced per hour
Whether the air change rate is adequate for common use cases
Frequently Asked Questions
What are air changes per hour (ACH)?
ACH measures how many times the total air volume in a room is replaced in one hour by the HVAC system. An ACH of 6 means the entire room volume of air is cycled through 6 times per hour. Higher ACH means better ventilation and air quality.
What ACH is recommended for different spaces?
Recommendations vary by use: homes need 4-6 ACH, offices 6-8, kitchens 15-20, hospital operating rooms 20-25, and clean rooms 30-60+. Bathrooms typically need 8-10 ACH. Local building codes specify minimum requirements for each space type.
How do I calculate the CFM needed for a room?
Multiply the room volume (length x width x height in feet) by the desired ACH, then divide by 60. For a 1,000 cubic foot room needing 6 ACH: 1,000 x 6 / 60 = 100 CFM. This gives you the minimum airflow rate for your HVAC or ventilation system.
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