Chapter 5 Basic Duct Symbols and Drawings 89
Copyright Goodheart-Willcox Co., Inc.
5.1.1 Anatomy of a Duct System
Air distribution systems vary based on the require-
ments of the space, but all have the same basic com-
ponents and perform the same function. A system’s
ductwork consists of return air and supply air sec-
tions. Return air ducts carry air from the conditioned
space to an air handler, while supply air ducts deliver
the treated air to the conditioned space. An example
of an air distribution system is shown in Figure 5-1.
The air handler, which consists of a blower, heat trans-
fer surfaces, and sometimes air cleaning and fi ltering
media, is located between the return and supply ducts.
Connected to each side of the air handler are plenums,
which are chambers for treated air leaving an air-
conditioning unit that connect to primary supply and
return trunks.
A primary supply trunk carries all of the air
treated by the air handler. From the primary sup-
ply trunk, treated air is then distributed, via the net-
work of supply ducts, back to the conditioned space.
A primary return trunk carries all of the air from
the conditioned space to the air handler. A primary
supply trunk can feed air into secondary supply
trunks and branch runouts, as shown in Figure 5-2.
Return grille
Secondary
return trunk
Takeoff fitting
Supply
register
Branch runout
Secondary
supply trunk
Branch runouts
Air handler
Primary
return trunk
Return plenum
Supply plenum
Primary
supply trunk
Goodheart-Willcox Publisher
Figure 5-1. A sample air distribution system.
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Figure 5-2. The primary supply trunk supplies air to branch
runouts and/or secondary supply trunks.
Branch runout
Secondary
supply trunk Branch runouts
Supply plenum
Air handler
Primary
supply trunk