Ventilation Rate Calculator (CFM & ACH)
Room Dimensions
Airflow Standards
Ventilation Requirements
*CFM = Cubic Feet per Minute required to meet the target air exchange rate.
How to Calculate Ventilation Rates
Proper ventilation is crucial for indoor air quality (IAQ), controlling humidity, and removing contaminants. The standard metric for sizing HVAC systems, exhaust fans, and air purifiers is CFM (Cubic Feet per Minute) based on a desired ACH (Air Changes per Hour).
This calculator helps engineers, contractors, and homeowners determine the required fan size for a specific room volume.
The Ventilation Formula
To calculate the required airflow in CFM, we use the following equation:
CFM = (Room Volume × Target ACH) / 60
- Room Volume: Calculated as Length × Width × Height (in cubic feet).
- Target ACH: The number of times the total air volume in the room needs to be replaced in one hour.
- 60: Conversion factor from hours to minutes.
Common Air Changes per Hour (ACH) Guidelines
Different spaces require different ventilation rates depending on their usage and occupancy density. Below are general guidelines based on ASHRAE standards and common practices:
| Room Type | Recommended ACH |
|---|---|
| Residential Bedroom / Living Room | 4 – 6 |
| Residential Kitchen / Bathroom | 8 – 15 |
| Offices / Conference Rooms | 6 – 10 |
| Classrooms | 6 – 12 |
| Laboratories / Medical Facilities | 10 – 20+ |
| Server Rooms | 20 – 30 |
Example Calculation
Imagine you have a standard office room with the following dimensions:
- Length: 20 feet
- Width: 15 feet
- Height: 10 feet
First, calculate the volume: 20 × 15 × 10 = 3,000 cubic feet.
If you want 6 Air Changes per Hour, the math is:
(3,000 ft³ × 6 ACH) / 60 = 300 CFM.
You would need a fan or HVAC supply capable of delivering 300 CFM to properly ventilate this office.