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Test the bathroom fan by holding a tissue up to the grille with the fan running; it should hold the tissue firmly. Clean the grille and the fan blades a couple of times a year, and once a year confirm from the attic or outside that the duct actually carries the air to a roof or wall cap. A fan that fails the tissue test, or that vents into the attic, is the usual reason a bathroom grows mold no cleaner can keep up with.
The fan's job is to move the shower's moisture out of the house before it condenses on the walls, the ceiling, and, worst, inside the wall cavity and the attic. A weak fan or a fan venting into the attic does the opposite: it moves the moisture to where you cannot see it.
How do you do the tissue test?
Turn the fan on. Hold a single square of toilet paper or a tissue flat against the grille and let go. A fan that is working holds it there. A fan that lets it fall is not moving enough air, either because it is clogged, the duct is blocked or disconnected, the damper at the end is stuck, or the fan is undersized or worn out. Do the test in every bathroom; it takes ten seconds each.
What do you need?
A stepladder, a vacuum with a brush attachment, a soft brush, a damp cloth and a little dish soap, a screwdriver if the grille is screwed on (most pull down on spring clips), and a flashlight for the attic check. Half an hour for one fan; the cleaning is ten minutes and the venting check is the rest.
- A stepladder
- A vacuum with a brush attachment
- A soft brush, a damp cloth, and a little dish soap
- A screwdriver, if the grille is screwed on (most pull down on spring clips)
- A flashlight for the attic check
What are the steps for cleaning the fan?
Switch the fan off (and its breaker if you will touch anything past the grille), pull the grille down and wash it, vacuum and wipe the blades or blower wheel until they spin freely, vacuum the housing without spraying the motor, check the damper flap swings freely, replace the grille, and repeat the tissue test. A wheel packed with dust is the usual cause of a weak, loud fan.
- Turn the fan off at the switch, and turn off its breaker if you will be touching anything beyond the grille.
- Pull the grille down. Most are held by two spring clips that you squeeze together to release. Wash the grille in warm soapy water and let it dry.
- Vacuum the fan housing and the blades or the blower wheel with the brush attachment. Wipe the blades with the damp cloth. A blower wheel packed with dust is the usual cause of a weak, loud fan. Done when: the blades are clean and spin freely by hand.
- Vacuum the motor and the housing. Do not spray anything into the motor.
- Look at the damper flap where the duct leaves the housing; it should swing freely and close on its own.
- Replace the grille. Turn the fan on and repeat the tissue test. Done when: the tissue holds.
What are the steps of the venting check?
From the attic, follow each fan's duct to a roof or wall cap and reconnect or extend anything that ends in the attic, points at a soffit, or has come apart; from outside, run the fan and confirm the cap's damper opens and air comes out, clearing lint, nests, and paint. A duct that ends in the attic is dumping every shower's moisture into the insulation.
- From the attic, find the duct from each bathroom fan. Follow it. It should run, with as few sags and bends as possible, to a roof cap or a wall cap, and be connected at both ends. The attic check covers the rest of what to look at while you are up there.
- A duct that ends in the attic, points at a soffit vent, or has come apart at a joint is dumping moist air into the insulation. Reconnect it with foil tape and clamps, or extend it to a proper cap, or have it done. Insulated duct in a cold attic reduces condensation inside the duct, which otherwise drips back into the fan.
- From outside, find each cap. Run the fan and confirm the damper opens and air comes out. Clear lint, nests, and paint from the damper.
Which habits make the fan work?
Run the fan during every shower and for fifteen to twenty minutes after; a timer switch that replaces the wall switch makes this automatic and is the single best bathroom upgrade under the cost of a dinner out. Leave the bathroom door open a crack while the fan runs so it has makeup air to pull; a fan in a sealed room moves little. Squeegee the shower walls and leave the shower door open afterward. The tile and grout guide explains why drying is the real mold control.
When should you stop and call a pro?
Call an electrician to replace a fan or to install a timer switch if you are not comfortable working in the ceiling box with the breaker off. Call a roofer or a handyman to add a roof cap where a duct has no proper termination.
Call a mold remediation company if you find mold inside the wall cavity or in the attic insulation beyond a small surface patch; that is not a fan problem anymore, it is a moisture problem that has been going on for a while. A bath fan with a built-in heater or light has more wiring; treat it as electrical work.
In a new home, a bath fan duct that was never connected to the cap is one of the most common defects found in first-year attic checks, and it is a builder item.
What should you record?
The date, the tissue test result for each bathroom, and where each duct terminates. If you replaced a fan, note the model and its rated capacity. Set the cleaning as a twice-yearly task and the venting check as a yearly one in the fall.
Common questions
How long should the fan run after a shower?
Long enough to clear the moisture, which is longer than most people leave it: fifteen to twenty minutes after the shower ends is a common recommendation, and a fan timer switch makes it automatic. If the mirror is still fogged when the fan stops, it did not run long enough or it is not moving enough air.
The fan is loud and moves almost no air. Replace it?
Clean it first; a fan choked with dust is loud and weak. If it is still weak after cleaning, check the duct for a disconnected or crushed section and the roof or wall cap for a stuck damper. If all of that is clear, a new fan is inexpensive and modern ones are far quieter; make sure the replacement's capacity suits the room.
Where should the duct end?
At a cap on the roof or an exterior wall with a damper that opens when the fan runs. Not in the attic, not at a soffit vent, not in a wall. The Department of Energy is specific that exhaust fans must not vent into the attic; doing so soaks the insulation and grows mold.
What should you do next?
Do the tissue test in every bathroom tonight. If one fails, clean it this weekend; if it still fails, look in the attic. The range hood and the dryer vent are the other two exhaust paths in the house, and the dryer vent has its own guide.
