Exhaust Fan Sizing Calculator
Calculate the exhaust fan CFM rating needed for bathrooms, kitchens, or utility rooms based on room volume and required air changes.
Fan Rating Needed
85 CFM
Fan Rating Needed vs Room Length
Formule
## Exhaust Fan Sizing **CFM = Room Volume x ACH / 60** The HVI (Home Ventilating Institute) recommends a simpler rule for bathrooms: 1 CFM per square foot for rooms up to 100 sq ft, and 50 CFM minimum. For larger bathrooms, add 50 CFM per fixture (toilet, shower, tub). Kitchens need 100-400 CFM depending on cooking.
Exemple Résolu
10 x 8 ft bathroom, 8 ft ceiling, 8 ACH.
- 01Volume = 10 x 8 x 8 = 640 cu ft
- 02CFM = 640 x 8 / 60 = 85 CFM
- 03Square foot rule = 80 CFM
- 04Use at least an 80-90 CFM fan.
Questions Fréquentes
What sone rating is quiet?
Under 1.0 sone is considered very quiet (leaves rustling). 1-2 sones is quiet operation. Above 3 sones is noticeable. Look for fans rated under 1.5 sones for bathrooms.
Does duct length affect fan performance?
Yes. Longer duct runs and more elbows create back-pressure that reduces actual airflow. Check the fan performance curve at your estimated static pressure, typically 0.1 to 0.25 inches of water.
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