01
Formula
CFM = length × width × height × air changes ÷ 60.
Reverse it when you already know the fan: air changes per hour = CFM × 60 ÷ cubic feet. The form solves for CFM from the air changes you type.
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CFM calculator for air changes per hour
This CFM calculator multiplies room volume by the air changes per hour you enter, then divides by 60. That is the airflow for a ventilation calculator. An air compressor CFM calculator is a different sum: add the CFM ratings of the tools you will run together.
Airflow
240CFM
Room volume2,400 cu ft
Air changes per hour6.00
Room airflow arithmetic. It is not a mechanical-code ventilation design, and it does not size ducts.
How it works
CFM is the room's volume turned over, per minute.
Cubic feet are length times width times height. Air changes per hour are how many times that volume is replaced in an hour. Divide by 60 because a cubic foot per minute is the per-minute rate. Six air changes in a 2,400 cubic foot room is 240 CFM. The 6 is an input, not a code minimum. A ventilation calculator for a shop, a booth, or a housing still has to meet the rule that applies. This page only does the multiplication. For an air compressor, do not use room air changes. Add the compressor CFM the tools require at the pressure you use, and size the compressor above that sum.
02
Example
A 20 by 15 by 8 foot room at 6 air changes per hour.
The room is 2,400 cubic feet. The airflow is 240 CFM. Change the air changes and the CFM moves in proportion. A compressor is not this room. If two tools need 8 CFM and 12 CFM at the same time, the air compressor CFM calculator sum is 20, plus the margin the manufacturer wants.
03
Tips
A fan's free-air rating is not the CFM in the duct.
Static pressure lowers delivered airflow. Use this number as the target, then read the fan curve. The page does not size duct or count elbows.
04
Equipment
The fan or compressor can be the equipment.
If the business is buying ventilation or shop equipment from $15,000 to $2 million, Dengaro can take the application. The CFM target is not the price.
Important questions
Know what to expect.
How is an air changes per hour calculator the reverse of this?+
Multiply CFM by 60 and divide by the room's cubic feet. This form goes the other way: you type the air changes and it returns CFM. Both use the same relationship.
What should a ventilation calculator use for air changes?+
The number the design or the applicable rule calls for. Six is only the value filled in so 240 CFM appears. It is not a recommendation for every room.
Why is an air compressor CFM calculator not the room formula?+
A compressor feeds tools, measured in CFM at a pressure. A room fan replaces air. Adding tool CFM ratings is the compressor estimate. Do not divide the shop's volume by 60 and call it the compressor.
Does this include make-up air or heat loss?+
No. It is the airflow volume. Heating that air is a separate BTU question on the BTU calculator.
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