Enter the total volume into the Calculator. The calculator will estimate the airflow rate (CFM) required for 3 air changes per hour (ACH). Note: dehumidifiers are typically “capacity” rated by moisture removal (e.g., pints/day or L/day), not by airflow.

Dehumidifier Airflow (ACH) Calculator

Enter one value to calculate the other (assumes 3 ACH)

Related Calculators

Dehumidifier Airflow (3 ACH) Formula

Q = V / 60 * 3

Variables:

  • Q is the estimated airflow rate (CFM)
  • V is the total volume (ft³)
  • 3 is the assumed air changes per hour (ACH)

To estimate airflow for 3 ACH, divide the total volume by 60, then multiply by 3. (More generally, CFM = V × ACH / 60.)

How to Calculate Dehumidifier Airflow (3 ACH)?

The following steps outline how to estimate the airflow rate corresponding to 3 air changes per hour (ACH).

  1. First, determine the total volume (ft³). 
  2. Next, gather the formula from above: Q = V / 60 * 3 (this assumes 3 ACH).
  3. Finally, calculate the airflow rate (CFM).
  4. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

total volume (ft³) = 300,000

Q = 300,000 / 60 × 3 = 15,000 CFM

Frequently Asked Questions

What is dehumidifier “capacity”?

Dehumidifier capacity is most commonly the moisture removal rate (for example, pints/day, L/day, or kg/h) under specified test conditions. Airflow (CFM) is a separate specification that describes how much air moves through the unit.

What does this calculator actually compute?

This calculator estimates an airflow rate based on room volume and an assumed ventilation/circulation rate of 3 air changes per hour (ACH). It does not determine how many pints/day (or L/day) of moisture removal you need.

Can I use the same formula for any room size?

You can use the relationship CFM = V × ACH / 60 for any space volume. However, the “right” ACH depends on the application (comfort, odor control, drying, ventilation needs, etc.), and dehumidifier moisture-removal sizing depends on the moisture load, not just volume.

How often should I check or replace my dehumidifier?

Regular maintenance (such as cleaning filters and ensuring the condensate drain is clear) is typically done every few months during use. Lifespan varies widely, but many residential dehumidifiers last roughly 5–10 years depending on usage, environment, and maintenance.