According to the guidelines of The Home Ventilating Institute (HVI) bathrooms up to 100 sq ft are sized at 1 CFM per sq ft of floor area. Bathrooms over 100 sq ft are sized by the fixtures in the room. Allow 50 CFM per standard tub, shower or toilet. Whirlpool, garden and jetted tubs are calculated at 100 CFM. Example: Bathroom 9’ x 7’ = 63 sq ft you require the PB100 or PBW110. Example: Bathroom 11’ x 14’ = 154 sq ft, 1 Toilet + 1 Shower + 1 Tub = 150 CFM you require the PB270-2. Note: HVI recommends that Steam Showers use a separate fan on a timer so that the fan may be shut off during shower use and then run afterwards to dry out the shower stall. For proper airflow in typical installations (when duct losses aren’t calculated) use the 0.4” WG (static pressure) rating point for the correct fan selection. Bathroom doors need to have at least ¾” clearance to the finished floor to allow for make up air.