Fixing a bathroom vent fan

Q: When I get out of the shower, the bathroom is completely fogged up, even when the exhaust fan is running. What’s the point of having a bathroom exhaust fan if it doesn’t clear the air? — Kurt C., Huntsville, Ala.

A: Good question. If a bathroom exhaust fan doesn’t do the job it’s advertised to do, what’s the point of having one?

The exhaust fan serves a good purpose. It draws moist air out of the bathroom, minimizing damage to wallpaper, baseboards, the ceiling and anything else that isn’t sealed against water. However, if a “fog” lingers for more than five minutes after a shower, the fan isn’t doing its job.

The problem could be a blocked exhaust duct, an ailing fan motor or a unit that’s not large enough to clear the entire room. In every case, the unit is not pulling enough air out of the bathroom. An exhaust fan should remove as many cubic feet of air each minute as the number of square feet of the bathroom’s floor space.

Clean dust and debris from the unit and air ducts. If cleaning the unit doesn’t help, consider replacing it.

Switch off the unit at the circuit box, then remove the front grille. Use a circuit tester to make sure no power is coming through the wires attached to the fan motor. Do this by placing one probe of the tester against each connector, then placing the second probe against the grounding screw on the fan housing. Don’t touch the bare wires with your fingers. If the tester glows at any point, go back to the circuit box and turn off the correct switch.

Remove the mounting screws and pull the fan out of the wall or ceiling cavity. Disconnect the vent hose and household wiring to free the unit, then set it aside.

Next, measure the fan’s wall or ceiling cavity and record it. Measure the square footage of the bathroom as well. Take those figures and the fan assembly to the home-improvement store and purchase a fan that works best for the room’s square footage. Make sure the new fan’s exhaust port matches the size of the old exhaust port.

Install the new fan in the old cavity, if possible (a larger unit may require you to increase the size of the cavity). Attach the fan housing to the stud or joist, avoiding the nail holes of the old unit.

Test the household wiring to make sure the power is off before attempting to connect them to the new unit.

Then, follow the manufacturer’s instructions to hook up the wires. Connect the vent hose to the new unit’s exhaust port, replace the grille cover and switch on the power at the circuit box.

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