Your bathroom has an exhaust fan.
While not required in every instance, in modern construction I think they are essential.
For this exercise let’s assume you have one. How do you know it works? “Well, I can hear it running,” you might say. OK—let me be a little more precise. How do you know it is “functional.” By functional I mean how do you know it is pulling air from the room. (For now we won’t discuss where it is going after it leaves the room—that will make the post too long.)
Home inspectors will not generally pull out expensive testing equipment to determine if the fan is functional. A simple test, that is highly unscientific, that does give us “some” indication of function is whether the fan will suck a tissue paper up against the grille. Another test is to put same tissue paper on the floor right at the bottom of the door to the room and then turn on the fan. If the fan sucks the tissue across the floor that is a pretty good indication as well that the fan is “functional” to some degree.
So let’s say that the fan does not hold a tissue paper and it does not move away from the door during operation. Both of these conditions can be caused by either a blocked exhaust on the fan or too tight a seal on the bottom of the door. We do not want to say replace the fan or figure out if the duct is blocked (perhaps bees have filled the cap with nests and the flap can’t open) if it is a simple matter that air cannot get into the room. One can open the door a little and then see if the fan will hold a tissue.
Another common problem that this simple test can reveal is what is pictured in the following picture.
The fan is indeed pulling air—-but is blowing it right back into the room on the other side of the grille. Ideally when running this test, the entire grille should be covered with tissue, but with experience the inspector can figure it out with partial coverage.