The Outside End of a Herriman Dryer Vent

What happens at the wall hood

A dryer vent terminates in a hood with a hinged flap that opens when the dryer runs and falls closed when it stops. That flap does two jobs: it lets exhaust out and it keeps weather, insects and rodents from coming in. Left alone for a few years it stops doing either.

Lint escaping the outlet catches on the flap and on the hood housing, and moisture in the exhaust turns it into a felt mat. Once that mat forms, the flap no longer swings freely, and a flap that only opens partway restricts the whole system no matter how clean the duct behind it is. On many of these houses the hood is set low on the wall, so it also collects drifting snow in winter and windblown grit and seed the rest of the year, and Herriman sits up against the Oquirrh foothills where the air moving down off the mountain drives all of that straight at whichever wall the hood happens to be on. And there is the landscaping problem: a bush planted at a sensible distance when the yard went in is pressed against the wall by the time it is mature.

Then there is the screen. People fit mesh over the outlet with entirely good intentions, usually to keep birds out. Mesh across a dryer outlet catches lint on the inside face and blocks solid, and it is the single most reliable way to disable a vent. The right answer to birds and rodents is a hood with a properly functioning flap, not a screen.

Cleaning the whole run

Inside, we clean the full duct length with rotating brushes on flexible rods, working from the appliance toward the outlet with vacuum containment at the machine so lint is captured rather than distributed around the laundry room. Then the parts get assessed: the transition hose between the machine and the wall, which should be rigid or semi-rigid metal rather than vinyl or thin foil and should be as short and straight as the space allows; the duct itself, which should be smooth-wall metal for its whole length; and the termination hood, which gets cleared and, where the flap has stopped working, replaced.

The reason to keep up with it is partly fire risk, since lint is dry, fine and readily ignited and a dryer supplies the heat. The reason you will actually notice is duller: clothes drying in one cycle instead of two, a laundry room that stops feeling humid, and a machine that is not straining against an obstruction every time it runs.