Exhaust Fan Sizing (CFM Rating)
Category: infrastructure
The mechanical airflow volume capacity required to safely exhaust moisture and prevent mold in a bathroom.
The Home Ventilating Institute (HVI) mandates a baseline standard calculation metric of one CFM per square foot of bathroom space. For example, an 8x10 bathroom requires an eighty-CFM exhaust fan to execute eight complete air changes per hour, safely venting high-humidity steam outside.
Common Examples
- We updated the ceiling ventilation to a high-capacity one-hundred-CFM exhaust fan to pull humidity out before mold could take hold.
- Venting a bathroom exhaust fan directly into an open, unconditioned attic space violates building codes, as it forces rot into roof rafters.