90 Print Reading for HVACR
Copyright Goodheart-Willcox Co., Inc.
A secondary supply trunk supplies air to branch runouts or other sec-
ondary supply trunks. Branch runouts are duct runs that carry air from a
takeoff fi tting to a boot, as shown in Figure 5-3. A boot is the duct fi tting
that connects the runout duct to the supply register, Figure 5-4. In some
installations, if local codes permit, fl exible duct can be used for the run-
out. Otherwise, rigid duct sections must be used.
Air distribution systems on smaller heating and air-conditioning sys-
tems typically only have branch runouts, because the supply registers are
typically close to each other. When the structure is larger, or when the
supply register locations are far from each other, secondary trunks are
often used. Secondary trunks carry a portion of the total amount of air.
Figure 5-5 shows how the primary supply trunk feeds air to the second-
ary trunks. The total airfl ow through all secondary supply trunks and
branch runouts connected to the primary supply trunk should be the
same as the airfl ow in the primary supply trunk.
5.2 Straight Duct Sections
The majority of ductwork consists of straight runs. Square ducts have
equal width and depth dimensions, such as 20″ × 20″ or 18″ × 18″. These
ducts are drawn the same on both plan and elevation views. When the
cross-sectional dimensions are different, as in the case of rectangular
duct sections, the sections are represented differently on plan and eleva-
tion views.
Consider a section of straight, horizontal ductwork with cross-
sectional dimensions of 28″ × 14″, Figure 5-6. When a duct section is
labeled on a drawing, the dimension listed fi rst represents the side that
is seen in the drawing. In Figure 5-6B, the 28″ side of the duct is shown
in the drawing. Since the duct is installed with its longer sides parallel to
the fl oor, this fi gure represents a plan view of this duct. Figure 5-6C rep-
resents an elevation view of the same duct section showing the 14″ side
of the duct. The 28″ sides of the duct are still parallel to the fl oor, but are
not seen in this view.
Takeoff
Primary or secondary
supply trunk
Branch runout
Boot
Supply register
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Figure 5-3. A branch runout connects the takeoff fi tting to the boot.
Goodheart-Willcox Publisher
Figure 5-4. One type of boot fi tting.
4-AA
Goodheart-Willcox Publisher
Figure 5-5. A primary supply trunk supplies
air to the secondary supply trunks.
Primary
supply trunk
Secondary
supply trunk
Secondary
supply trunk
Copyright Goodheart-Willcox Co., Inc.
A secondary supply trunk supplies air to branch runouts or other sec-
ondary supply trunks. Branch runouts are duct runs that carry air from a
takeoff fi tting to a boot, as shown in Figure 5-3. A boot is the duct fi tting
that connects the runout duct to the supply register, Figure 5-4. In some
installations, if local codes permit, fl exible duct can be used for the run-
out. Otherwise, rigid duct sections must be used.
Air distribution systems on smaller heating and air-conditioning sys-
tems typically only have branch runouts, because the supply registers are
typically close to each other. When the structure is larger, or when the
supply register locations are far from each other, secondary trunks are
often used. Secondary trunks carry a portion of the total amount of air.
Figure 5-5 shows how the primary supply trunk feeds air to the second-
ary trunks. The total airfl ow through all secondary supply trunks and
branch runouts connected to the primary supply trunk should be the
same as the airfl ow in the primary supply trunk.
5.2 Straight Duct Sections
The majority of ductwork consists of straight runs. Square ducts have
equal width and depth dimensions, such as 20″ × 20″ or 18″ × 18″. These
ducts are drawn the same on both plan and elevation views. When the
cross-sectional dimensions are different, as in the case of rectangular
duct sections, the sections are represented differently on plan and eleva-
tion views.
Consider a section of straight, horizontal ductwork with cross-
sectional dimensions of 28″ × 14″, Figure 5-6. When a duct section is
labeled on a drawing, the dimension listed fi rst represents the side that
is seen in the drawing. In Figure 5-6B, the 28″ side of the duct is shown
in the drawing. Since the duct is installed with its longer sides parallel to
the fl oor, this fi gure represents a plan view of this duct. Figure 5-6C rep-
resents an elevation view of the same duct section showing the 14″ side
of the duct. The 28″ sides of the duct are still parallel to the fl oor, but are
not seen in this view.
Takeoff
Primary or secondary
supply trunk
Branch runout
Boot
Supply register
Goodheart-Willcox Publisher
Figure 5-3. A branch runout connects the takeoff fi tting to the boot.
Goodheart-Willcox Publisher
Figure 5-4. One type of boot fi tting.
4-AA
Goodheart-Willcox Publisher
Figure 5-5. A primary supply trunk supplies
air to the secondary supply trunks.
Primary
supply trunk
Secondary
supply trunk
Secondary
supply trunk