All bathroom, kitchen and laundry exhaust fans should terminate at the exterior of the home—at vent caps with a back-draft damper.
These vent caps can be located on the roof, side walls, and occasionally even on the soffits of the home. These soffit vent caps are less common and I discourage their use unless there is just no other way to terminate the vent.
This first picture shows a wall vent installed on the soffit.
Due to gravity the back-draft damper can’t stay in the closed position and cold air, birds and insects can enter the duct.
The back-draft damper prevents cool air and vermin from entering the duct. Condensation might occur if the damper was not there and also wind could pull the damper in the exhaust fan open. This would exhaust heat from the home even when the fan was not running.
Too often I find these vents terminated inside the attic next to screened roof vents. This arrangement can result in clogging of the screen and result in the vented air ending up in the attic where moisture can do damage to the roof structure.
Many exhaust fans are found to be non-functional at the time of inspection. One simple test to determine if the fan is drawing air is to turn the fan on and see if it will hold a piece of tissue paper against the grille (unfortunately the test will not answer WHERE it is venting to). Another test (if your fans are too high to reach), is to turn the fan on and then put the tissue at the gap under the door to the room and watch to see if the air that should be moving into the room blows the tissue into the room.
It is a good idea to regularly check to make sure your exhaust fans are functioning properly.
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