Calculate dehumidifier airflow rate from room volume, or find total volume from airflow, using 3 air changes per hour in CFM or m³/min.
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Dehumidifier Airflow (ACH) Formula
This calculator uses 3 air changes per hour (ACH) as the default target. It calculates either the airflow rate needed for a room or the room volume that a given airflow rate can handle.
CFM = (V * ACH) / 60
V = (CFM * 60) / ACH
With the calculator default of 3 ACH, the formulas become:
CFM = (V * 3) / 60
V = (CFM * 60) / 3
- CFM = airflow rate in cubic feet per minute
- V = total room or space volume in cubic feet
- ACH = air changes per hour
- 60 = minutes per hour
If you enter the total volume, the calculator finds the airflow rate needed to move enough air for 3 ACH. If you enter the airflow rate, it finds the maximum volume that airflow can serve at 3 ACH. Metric inputs are converted to cubic feet or CFM internally before the result is converted back to your selected unit.
Common ACH Targets for Dehumidification
ACH targets vary by moisture level and how quickly you want air to circulate through the dehumidifier.
| Condition | Typical ACH Range | Notes |
|---|---|---|
| Light humidity control | 1 to 2 ACH | May be enough for mildly damp spaces with steady conditions. |
| General dehumidification | 3 ACH | This is the value used by the calculator. |
| Damp basement or crawlspace | 3 to 5 ACH | Higher airflow may help when air movement is limited. |
| Water damage drying | 5+ ACH | Often requires professional drying equipment and moisture monitoring. |
Quick Volume and Airflow Reference at 3 ACH
| Space Volume | Required Airflow at 3 ACH |
|---|---|
| 500 ft³ | 25 CFM |
| 1,000 ft³ | 50 CFM |
| 2,000 ft³ | 100 CFM |
| 3,000 ft³ | 150 CFM |
| 5,000 ft³ | 250 CFM |
Example Calculations
Example 1: Find the airflow rate
You have a room with a total volume of 2,400 ft³. Using 3 ACH:
CFM = (2400 * 3) / 60 = 120
The required airflow rate is 120 CFM.
Example 2: Find the supported volume
You have a dehumidifier airflow rate of 80 CFM. Using 3 ACH:
V = (80 * 60) / 3 = 1600
The airflow can serve about 1,600 ft³ at 3 ACH.
FAQ
What does ACH mean for a dehumidifier?
ACH means air changes per hour. For dehumidification, it describes how many times the air volume of the space passes through the dehumidifier each hour. A target of 3 ACH means the airflow should move three times the room volume in one hour.
How do I find the total volume of a room?
For a rectangular room, multiply length by width by height. For example, a 20 ft by 15 ft room with an 8 ft ceiling has a volume of 2,400 ft³. For irregular spaces, split the area into smaller rectangular sections, calculate each section, then add them together.
Is airflow the same as dehumidifier capacity?
No. Airflow is how much air the unit moves, usually in CFM or m³/min. Dehumidifier capacity is how much water the unit can remove, often listed in pints per day or liters per day. Both matter. A unit can have enough water-removal capacity but still perform poorly if air does not circulate well through the space.
