For bathrooms less than 100 square feet, determine the room’s CFM requirements by measuring and multiplying the length, width and ceiling height of the room, then use the multiplication factor of .13 and round up to the next “ten.” For example: 10’ long x 8’ wide x 9’ height x .13 = 93.6, select a bath fan with at least 100 CFM. If the bathroom is larger than 100 square feet, www.HVI.org recommends that you add the CFM requirement for each fixture present - a toilet is 50 CFM, a shower is 50 CFM, a bathtub is 50 CFM and a jetted tub is 100 CFM. For more information download the BROAN Ventilation Fan Catalog and review pages 6 and 7 or call our Technical Support Team at 800-637-1453.