The Home Ventilation Institute(HVI) recommends that bathrooms up to 100 square feet be ventilated by intermittent or continuous ventilation with an exhaust fan that provides airflow of at least 1 Cubic Foot per Minute (CFM). For an 8×5 bathroom, a 40 CFM unit is recommended (multiply to yield the CFM: 8×5=40). Bathrooms over 100 square feet should be ventilated according to fixtures. A toilet, shower, or tub each require 50 CFM. A jetted tub requires at least 100 CFM. Each fixture is added to the total. If a bathroom has a toilet, jetted tub, and separate shower, the CFM recommendation would be 200.
To meet the CFM requirements for airflow, a single, high CFM fan – or more than one fan with smaller CFM ratings – can be installed at strategic exhaust points. Fans can be placed over or near tubs and showers, and in separate, enclosed toilet rooms. Multiple exhaust ports can also be used with an in-line fan system.
To provide the most efficient bathroom ventilation for a home or building, install bathroom fans with the minimum recommended CFM to keep heat and moisture at bay. Following these guidelines will give the maximum results when it comes to air quality and building integrity.