The Home Ventilating Institute (HVI), a trade association representing the manufacturers of 95% of the residential fans in North America, recommends that a bathroom exhaust fan be selected that is capable of providing eight air changes per hour (ACH). Most building codes only require a minimum airflow of 50 cfm from a bathroom, with a capacity of providing five ACH. HVI also recommends that the kitchen ventilation fan (not the range hood) be sized to provide 15 ACH and in other rooms be sized to provide six ACH. Marley feels that the designer should use the more optimal ventilation rates recommended by HVI. The following tables reflect the HVI sizing guidelines and assume metal duct and a reasonable roof jack or weather cap. If flexible or semi-rigid duct is used, add ten feet of duct run for your fan selection calculation to allow for the higher static pressure created.
Airflow Estimator for Bathroom Fans
Enter Bathroom Length