Bathroom Exhaust Fan Cathedral Ceiling . Bathroom vent fans are rated by the cubic feet per minute (cfm) of air they move and should be sized to replace the air in the room at least eight times an hour. 180 cfm and has a 7.5 sone. Delta BreezSlim SLM100 4 Inch Quiet Bathroom Exhaust Fan, Ceiling or from www.walmart.com The only problem i see is you will be stopping the free flow of air from your eave vents to the ridge vent in that particular section. Broan makes an efficient and affordable bathroom exhaust fan that's a good pick for homeowners on a budget. The bathroom exhaust fan is a must for the ones that don’t have a window for ventilation.