Instructions / Assembly

Heating and Cooling Essentials
Branch piping
Register
boot
Plenum
Furnace
Side takeoff
Extended
plenum
Figure 28-8. Round branch piping extends outward from an extended pienum formed with rectangular duct.
28.4 Distribution System Components-^
The "supply air" distribution system includes the
plenum, the main trunk line, and all the branches serving
different living spaces. Each branch terminates in a
register that directs and usually controls the volume of
the airflow. Another system of air duct serves to return
air from the living spaces for heating or cooling. This
system is called "return air," and includes another
main trunk line and all its branches.
28.4.1 Plenum (Bonnet)
The first fitting to be installed on any system is the
plenum, sometimes called a bonnet. Figure 28-9. It is
usually made of 30-gauge, galvanized sheet metal,
forming a chamber that is attached to the furnace
outlet, Figure 28-9A. The plenum functions as an air-
mixing chamber before sending the air to the living
spaces. It also provides the necessary surface for
attaching takeoffs and starting collars. The cooling
Plenum parts
Plenum kit
with evaporator
A B C
Figure 28-9. A plenum can be fabricated in the field (A, B) or it may be assembled from a factory kit (C).