Option 3 - Combination System
The combination system may be used in high-rise apartments,
with a bank of dryers installed at several different levels. Each of
these banks then exhausts into a central vertical vent. See the
following illustration for an example of a combination system.
A. Central vertical duct - maximum of
0.1" (2.5 mm) water column vacuum
B. Weighted damper (each dryer)
C. Maximum back pressure measurement
D. Barometric damper (use depends on
exhaust system design)
E. Outside air source
Frequency of Exhaust System Cleaning
Every exhaust system must be inspected periodically and cleaned
to ensure that it is intact and free from lint accumulation. The
frequency of these inspections will vary, depending on the system
and usage of the dryer. For single-family usage, an annual
inspection is recommended. In commercial usage or in multiple
dryer systems, a more frequent inspection is recommended.
Complaints of long drying times or a hot dryer top indicate the
need for inspection of the exhaust system.
Inspecting the Exhaust System
1. Disconnect the exhaust duct from the dryer and from the
exhaust hood (at the exhaust outlet) outside of the building.
2. Inspect the interior of the duct and remove any lint
Be sure that lint is removed from the exhaust hood. Lint
may collect in the exhaust hood so that the flappers or
louvers will not open or close completely.
After cleaning the exhaust hood, check that the flapper or
louvers move freely.
3. Reassemble the exhaust duct and hood, checking that the
joints are secure.
4. Operate the dryer and verify that the exhaust air is not
obstructed in the vent and that there are no leaks in the
Seal any leaks found.