Bathroom exhaust fan condensation. Water stains on the ceiling around your bath fan may indicate a leak coming from the vent cap on your roof but condensation is the more likely culprit. It should be insulated straight and vented to the outside. In places where humidity is high for example in England UK then a fan might not be enough. The usual cause is condensation inside the duct. On Feb 24 2010. In general water dripping from the bathroom fan is caused by water condensation due to lack of insulation on the exhaust hose or duct lack of proper airflow due to vent blockage or improperly installed bathroom fan. Then it runs back down the duct to drip out of the fan into the room.
Check The Damper At The Fan. Bathroom exhaust has a very high dew point. If the cool exhaust is inside while it runs down the hot attic the temperature difference can result in condensation. When this is the case warm moist air from the bathroom can condense on the inside of the cold duct and can run back down into the bathroom. The fan should pull out any condensation that forms inside the bathroom. With insulation condensation will occur much higher up but it will happen.
The bathroom fan starts dripping when warm moist air condensates in an uninsulated or poorly insulated ventilation duct. Bathroom exhaust has a very high dew point. One of the tried-and-tested tools to get rid of condensation is an extractor or exhaust fan. The fan should pull out any condensation that forms inside the bathroom. The problem reduced somewhat the bathroom ceiling no longer has condensation. We then installed an additional damper within each bathroom duct in addition to the damper that is part of the fan unit and insulated the ducts.