Free HVAC CFM Calculator
HVAC CFM Calculator
Calculate Your Room's Required CFM
Enter the room dimensions and target air changes per hour. The calculator uses the room volume and ACH to estimate the airflow required for the space.
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THE ACH METHOD — A SIMPLE WAY TO ESTIMATE ROOM AIRFLOW
CFM measures the volume of air flowing through a space per minute. A system can have enough rated cooling capacity but still leave a space uncomfortable if the ductwork does not deliver the airflow the room requires.
The air-changes-per-hour method provides a simple way to estimate room-level airflow:
CFM = Room Volume × ACH ÷ 60
Set a preliminary ACH target appropriate to the application, and the estimated CFM follows from the room’s volume.
ACH as a preliminary reference
ACH can provide a simple way to estimate airflow from room volume, but the appropriate target depends on the application. Do not treat a fixed ACH value as a universal HVAC supply-air requirement. For equipment and duct design, use the applicable heating and cooling loads and professional HVAC design methods.
HOW TO USE THE HVAC CFM CALCULATOR
Use the calculator to estimate the airflow a room needs based on its volume and target air changes per hour. The result is a preliminary airflow estimate, not a substitute for a full HVAC design.
Once you have the number, it can serve as a preliminary airflow reference. Final register, duct, and equipment sizing should be based on the applicable heating and cooling loads, equipment requirements, and professional HVAC design methods.
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WHAT GOES IN
Use the calculator above, or run it yourself.
- 1. Measure the room. Enter the room's length and width in feet.
- 2. Enter ceiling height. Use the ceiling height in feet. Room volume is calculated as length × width × height.
- 3. Set the target ACH. Choose an appropriate air-changes-per-hour target based on the room type.
- 4. Read the CFM. The calculator uses the room volume and ACH to estimate the required airflow.
- 5. Cross-check the result. Use the estimated CFM as a preliminary reference for register count and rough system capacity. A common preliminary rule of thumb is approximately 100 CFM per 6-inch round register and 400 CFM per ton, but actual register, duct, and equipment requirements depend on the HVAC design, equipment, and manufacturer requirements.
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