When a dryer vent needs cleaning, and how often.

Warning signs

• Clothes take more than one cycle to dry.
• The dryer or the laundry room is hot to the touch.
• A burning or musty smell when the dryer runs.
• The exterior vent flap doesn't open, or lint collects around it.
• Lint builds up around the filter housing.

What to do yourself

1. Clean the lint filter after every load.
2. Wash the filter with soap and water now and then to remove the film left by dryer sheets.
3. Keep the area around the dryer clear.
4. Check the outside vent while the dryer runs. Air should push the flap open.

The duct matters

Rigid or semirigid metal duct is best. Vinyl or foil accordion duct traps lint and can sag and kink. Keep the run as short and straight as practical, and don't screw the joints, because screws catch lint.

How often to clean

At least once a year is the common advice, and sooner for a long run, a big family or a gas dryer. Gas dryers also vent combustion gases, so a blocked vent is a carbon monoxide risk.