Is it acceptable to route a bathroom exhaust fan to the return of a central air system? I'm afraid this will cause mold to grow in the air return ducts. There is currently a fan in our bathroom and I can't seem to find any separate outlet or vent for it, so I assume that it must be connected our central air system somehow. What is the best practice for routing bathroom fans if mold is a concern?
While it may be acceptable to vent into the central heater during winter when humidity is low, it is a terrible idea year round. The humidity load of the bathroom vent air is just too high. You want an external vent. And you very much want to trace that vent... if it goes to the attic that's quite bad.