A bathroom exhaust fan that has gone quiet, or that moves less air than it used to, is a job people put off until the mirror fogs and stays fogged. Replacing one is a sequence of small decisions, and the order matters: check, measure, get a written scope, schedule, install, test, and file the paperwork. This walks that sequence from the first look to the final check.
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Step one: confirm what is failing
Stand in the bathroom with the fan on and the door shut. Notice whether it hums, rattles, or does not pull air. Hold a square of tissue near the grille. If the tissue does not move, the fan is not working or the duct is blocked. Check the light and the fan switch separately, since they may run on separate controls. Ask the person at the house what the fan sounds like and how long it usually runs.
Step two: measure the opening and the duct
Note the size of the grille opening in the ceiling, the diameter of the round duct connection on the fan housing, and whether the duct runs to an outside wall or a roof cap. The new fan has to fit the same ceiling opening and connect to the same duct size, or the job turns into a remodel. Note how the old fan is held in place, by brackets or a housing. Photograph the label on the old unit, which lists the model and the electrical details the installer will need.
Step three: get a written scope
Ask each company to list the work: removing the old unit, installing the new one, any duct work, any drywall or paint repair around the opening, the electrical connection, and the final test. Ask whether the duct vents outside. A fan that dumps moist air into the attic causes its own problems. Ask whether the job needs a permit where you live and who pulls it. Ask who cleans up the dust and what happens to the old unit.
Step four: install day
The power is shut off at the panel before anyone touches the wiring. The old unit comes out, and the duct is checked for loose joints and cleaned at the opening. The new housing is set, the duct is connected and sealed with tape, the wires are connected, and the grille goes on. Ask the installer to run the fan and show you the air moving at the grille with the tissue test. Ask where the switch is and whether there is a timer, and how long the fan is set to run.
Step five: the walk-through and the folder
Before the crew leaves, run the fan, repeat the tissue test, look at the ceiling for new marks, and check the outside vent from the yard if you can see it. Keep the manual, the receipt, the warranty card, and the written scope together in one folder. Write the install date on the front in your own hand so the next person knows when the unit went in and where the paperwork lives.
Tonight
Go in with a phone and a tissue. Run the fan, note the noise, and check the switch. Photograph the grille and any label you can read. If you can see the outside vent from the yard, photograph that too. Send the photos to whoever will quote the job, and ask them to put the duct connection, the outside vent, and the cleanup on the written scope.