The Exhaust Fan Calculator is a ventilation design tool that determines the required airflow capacity (measured in CFM – cubic feet per minute) for an exhaust fan based on the room’s size and its intended use. This ensures that the air in a space is properly replaced within a recommended number of air changes per hour (ACH), helping maintain indoor air quality and meet building codes.
This calculator is especially useful for HVAC professionals, contractors, facility managers, and homeowners planning to install or upgrade exhaust systems in kitchens, bathrooms, workshops, or other enclosed areas. Proper exhaust fan sizing improves energy efficiency, reduces humidity, and prevents the buildup of contaminants or odors.
Formula of Exhaust Fan Calculator
Exhaust Fan CFM = (Room Volume × Air Changes per Hour) / 60
Where:
- Room Volume = Length × Width × Height (in cubic feet)
- Air Changes per Hour (ACH) = Number of times air in the room is replaced every hour
- 60 = Minutes in an hour, used to convert to CFM (cubic feet per minute)
Full Expanded Formula:
Exhaust Fan CFM = (Length × Width × Height × ACH) / 60
The ACH value varies by room type. For example:
- Bathrooms: 6–12 ACH
- Kitchens: 15–30 ACH
- Laboratories: 10–20 ACH
- Garages: 6–20 ACH
Using the right ACH ensures that the selected fan can handle the required airflow efficiently.
Exhaust Fan Sizing Quick Reference Table
This table provides estimated CFM values for typical room sizes and uses. These common benchmarks can guide users when choosing fans for standard installations.
| Room Type | Size (ft) (L×W×H) | Volume (ft³) | Recommended ACH | Required CFM |
|---|---|---|---|---|
| Bathroom | 8 × 6 × 8 | 384 | 10 | 64 |
| Kitchen | 12 × 10 × 9 | 1,080 | 20 | 360 |
| Laundry | 10 × 8 × 8 | 640 | 8 | 85 |
| Workshop | 15 × 12 × 10 | 1,800 | 15 | 450 |
| Garage | 20 × 15 × 10 | 3,000 | 10 | 500 |
This table helps in quickly identifying appropriate fan capacities based on room type and dimensions.
Example of Exhaust Fan Calculator
Let’s say you want to install an exhaust fan in a kitchen that measures 12 ft by 10 ft with a ceiling height of 9 ft. You decide on 20 air changes per hour.
Step 1:
Room Volume = 12 × 10 × 9 = 1,080 ft³
Step 2:
Exhaust Fan CFM = (1,080 × 20) / 60 = 21,600 / 60 = 360 CFM
So, a fan with at least 360 CFM capacity is recommended for effective ventilation in this kitchen.
Most Common FAQs
This calculator falls under the HVAC and indoor air quality tools category. It is commonly used in construction planning, home improvement, and mechanical ventilation design.
The ACH determines how frequently indoor air is replaced. This is critical in spaces like kitchens and bathrooms where odors, humidity, and pollutants can build up quickly. Choosing the right ACH helps maintain safe and comfortable air conditions.
While a higher CFM can improve ventilation, oversizing may lead to increased energy use and noise. It’s best to match the fan size closely with the calculated requirement for optimal performance and efficiency.