A bathroom fan has one job: move moist air out of the house. Not out of the room, not up into the ceiling, out of the house. Every hot shower puts a surprising volume of water into the air, and that moisture goes somewhere. It condenses on the coldest surface it can find, which is usually a window, an exterior wall, or the underside of the roof deck if the fan has quietly been sending it up there.
The reason this is easy to ignore is that the consequences are slow and indirect. Nobody ever notices humidity leaving a room correctly. What people notice eventually is paint peeling along the ceiling line, a door that swells in its jamb every winter, black spotting at the top corners of the shower wall, or a mirror that takes forever to clear. Those are all the same problem wearing different clothes.
Fans get specified by how much air they move, and the fan that came with the house was frequently chosen because it was the one on the shelf that day rather than because anyone matched it to the room. Bigger bathrooms, higher ceilings, and enclosed toilet compartments all need more than a small builder-grade unit can provide. An undersized fan runs and runs and still loses ground against a hot shower.
Duct routing makes it worse. Every elbow, every foot of flexible duct, and every sag in a run costs the fan performance it was rated for on a straight, short path. A fan that is technically adequate on paper can be quietly inadequate in practice because of what happens after the housing. If your fan runs, sounds like it is working, and the mirror still stays fogged, the size or the duct run is losing the argument.
This is the one that surprises homeowners the most, and it turns up constantly. The fan is connected to a duct, the duct goes up into the attic, and then it simply ends. No roof cap, no wall cap, no path out of the building at all. Every shower anyone has taken in that room has been pumping warm wet air directly into the attic, where it meets cold framing and roof sheathing and condenses.
Sometimes there is a cap on the roof and the duct fell off it years ago, which produces the same result with better intentions. The evidence lives above your ceiling: dark staining on the underside of the roof deck, compressed and damp insulation near the fan, occasional drips that look like a roof leak but track back to the bathroom. If you can safely look into the attic above your bathroom, look. It is the fastest inspection in this whole guide.
Start with the mirror. If it stays fogged long after the shower ends, air is not being exchanged fast enough. Then look at the top corners of the shower wall and the ceiling above it, where spotting and discoloration begin. Check the paint at the ceiling perimeter, and check whether the bathroom door has started to stick in humid weather. Utah air is dry most of the year, which fools people into assuming a bathroom takes care of itself.
There is also the simple test of holding a square of tissue up against the fan while it runs. If the tissue does not hold up there on its own, the fan is not moving meaningful air, whatever noise it happens to be making. Noise is not airflow. A loud fan that has run for years can be doing very little except reassuring the household that something is being handled.
The right moment to fix ventilation is during a remodel, when the drywall is down and everything is reachable. A correctly sized fan, ducted with smooth rigid pipe on as short and straight a run as the framing allows, insulated where it crosses cold space, and terminated at a proper roof or wall cap with a working damper. That is the whole fix, and relative to everything else in a bathroom project it is a small line item.
It is also worth thinking about controls while you are in there. A timer or a humidity-sensing switch keeps the fan running after the shower ends, which is exactly when it does the most useful work, and it removes the need for anyone in the house to remember. If the ceiling is already open for lighting or a new shower, correcting the fan and its duct is the least glamorous and most valuable item on the list.
It should not. Venting into an attic takes the moisture out of the room and deposits it on cold framing and roof sheathing, where it condenses and causes exactly the problems the fan was installed to prevent. The duct needs to terminate outside the building through a roof or wall cap with a damper.
Long enough for the room to actually clear, which is usually well past the point most people switch it off. A timer switch or a humidity-sensing switch handles this without anyone thinking about it, and it is one of the easiest upgrades to make while the wiring is accessible during a remodel.
Not reliably. A window depends on someone opening it, on outdoor temperature, and on which way the air happens to be moving. In cold months nobody opens it. A fan ducted to the outside works the same way in January as it does in July, which is the entire point of installing one.
A few details about the room and the house is all we need to start. Or call 801-644-9000.