Should dryer and bath fans ductwork pitch outside or back in the house?

Im trying to help my girlfriends dad out. He ran all his exhausts with schedule 40 pvc pipe instead of ductwork. He connected the inline fans and an additional damper… Im trying to help my girlfriends dad out. He ran all his exhausts with schedule 40 pvc pipe instead of ductwork. He connected the inline fans and an additional damper…Read MoreGreenBuildingAdvisor