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SECTION ONE
The Exhaust Requirements
Minimizing the length of ductwork and the number of turns in an exhaust system
minimizes the potential for lint to settle and accumulate in the exhaust duct and in the
interior cabinet of the dryer. Refer to your specific dryer installation instructions for
recommended permissible maximum duct length.
1. Wall Caps and other Terminations
All exhaust systems must be terminated in a manner that will prevent back drafts from
outdoors as well as prevent birds or other wildlife from building nests or taking refuge in
the ductwork. The wall cap should present minimal resistance to the flow of exhaust air
and should prevent lint and water accumulation and prevent clogging.
The preferred termination is either a dampered wall cap having a 4" wide opening
or a movable louvered wall cap.
A two and a half inch wall cap resists airflow and increases drying time. It must be
installed with the opening down and should be installed at a minimum of 12 inches above
ground level or any other obstruction. Special consideration should be given in areas
where heavy snowdrifts are likely to occur to ensure the wall cap does not become
obstructed. Other types of terminations, such as roof vents or louvered plenum chambers,
are acceptable providing they are equivalent to the 4" dampered wall cap. They must
contain at least 14 square inches of ventilation area and afford adequate protection
against back drafts
Exhaust ducts must not contain screens or other filtering devices anywhere along
their full length. They become clogged with lint and become a safety hazard.
The dryer exhaust must not terminate in an ordinary chimney, under an enclosed house
floor or crawl space, or into an attic, since any accumulated lint could create a fire hazard
and the moisture could cause damage. Never terminate the exhaust into the common
duct or plenum with a kitchen hood exhaust since the combination of grease and lint
could create a fire hazard.
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