We have two bathrooms side by side on our second floor. They both have the same exact layout (about 6'x7'). Both have their own separate exhaust fans (Nutone, 80CFM, 1.6amps), but share the same vent to the roof through a Y-shaped connector and flex 4" pipe. When we take steamy showers in bathroom A, paint from the ceiling of bathroom B is showing signs of moisture and paint is peeling in one area of the ceiling. We even noticed some condensation on the tile wall of bathroom B.
What could be causing the problem in bathroom B and how can we fix it?