My "A-frame" type house was built in 1974. Im removing and replacing the bathroom exhaust fans, which seem to be original to the house. They are noisy, undersized, ineffective, and were attached to wall/ceiling with flanges before drywall was applied. So, they were difficult to remove. The fans all have 3" diameter flexi-plastic exhaust ducts. The fans on the main floor and upper floor exhaust upward to the roof. BUT, there are no exhaust penetrations for the fans in the roof! It seems that the ducts go up to the top of the A-frame, and possibly terminate (not sure how) at the roofs ridge vent (which runs along the lenght of the roof). 1) Is this normal? Is it OK? 2) Most (if not all) exhaust fans these days have 4" diam. exhaust ducts. Are 3" diam. models available? If so, what company/source? Also, has anyone had experience with transitioning a 4" fan to a 3" duct? I know its not supposed to be done (reduced airflow, higher noise level, etc.) but I may not have a choice. Any suggestions?