All vents from 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 or side walls of the home.  There are caps made for soffits----although these 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 from entering the duct where condensation might occur if it was not there. 

     Often these vents terminate 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. 

   This next picture shows a very clogged screen where the vent pipe is near the screen.

      This next picture shows several vents all "aimed" at the same attic roof vent.

      Another popular place to terminate vents is on the inside of bird-blocking at the screened holes in the bird-blocking.   These vents quickly clog rendering the vent non-functional, resulting in the exhausted air ending up in the attic or staying in the room itself.  A variation of this approach is when a screened & louvered type cap is installed on the vent.  The bathroom vented to this location was not exhausting any air.

     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. (I can already see some of my favorite bloggers running off to check their exhaust fans)

Charles Buell 

     PS, for those of you that are new to my blog (or for some other "unexplained" reason have never noticed) all  pictures and smiley-face inserts (emoticons) have messages that show up when you point at them with your cursor.