Updated: Apr 11, 2019
So you run the bath exhaust fan to remove moisture – but then you get that drip, drip,
drip from the fan on your nice clean rug. Bath exhaust fans should not drip. If yours does, there’s something wrong with it.
First, check the exhaust ducting or tubing; it should be insulated, straight and vented to the outside. There should be a minimum of bends for proper air flow. If there is no insulation around the duct, the problem could be condensation in the cold duct. Adding insulation around the duct may solve the problem.
The fan’s damper can also get stuck in the open position, allowing hot air into the cool duct and creating condensation. Check the small damper at the fan. It should open when the fan is on and close when the fan turns off. This damper responds to fan pressure and gravity.
Most vent connectors through the roof or sidewall should also have a damper to keep cold air out, and it should open and close with fan operation.
For many years, contractors installed bath fan vent ducting incorrectly, creating a bend or low loop to catch condensation. This just allows water to accumulate and may cause a large leak when the water lets go.