Instructions / Assembly

Chapter 28 Ductwork
Keep pipes at least one inch from joists and other
combustible material. To prevent heat loss, metal duct is
often wrapped with insulation, Figure 28-36. If insu-
lating material is appl ied after the duct is already in place,
the insulation will have to be slit or stripped to get
around the supporting strap or wire. This opening must
be rescalcd to maintain insulating effectiveness.
Insulation Pipe
Roof joist
Strapping
Insulation Strapping
Figure 28-36. Duct is often located in the basement and
hidden between floor joists. When located in the attic, it is
hung with strapping attached to roof joists. Insulation is often
wrapped around the duct to prevent heat loss.
28.12 Working with Insulated
Flexible Duct -
Insulated flexible duct can be used for main trunk
line runs; it also can be used as branching duct,
Figure 28-37. This type of duct is available in a variety
of sizes, insulation thickness, and specifications,
Figure 28-38. Check local building codes for the exact
R-value required in your area. To prevent reduced
airflow, insulated flexible duct must be fully extended
when installed. Avoid any abrupt turns. When a sharp
turn is necessary, cut the flex duct at the turn and
install a 90-degree elbow of the same diameter. Do not
use wire to support flexible duct. Instead, use a wide
fabric strapping material and anchor it to wood
framing with staples.
28.12.1 Making Connections
Making connections with insulated flexible pipe is
not difficult, but must be performed properly to obtain
Figure 28-37. Insulated flexible duct used for a branch line
in a commercial application. The diffuser is sized to drop into
the suspended ceiling grid.
Figure 28-38. Different sizes and insulation thicknesses are
available in insulated flexible duct.
correct airflow and prevent leaks. Figure 28-39 shows
the connection procedure step-by-step.
28.13 Wall Stack
Wall stacks, Figure 28-40, transport air vertically,
from floor to floor. In residential applications, stacks
carry air to high-wall or second-floor registers from a
basement or crawl space. They can also be used to
carry air to baseboard or low-wall registers from attic
piping.
28.13.1 Installing Wall Stack
If possible, work from the basement. As each
section is attached, push the stack up into the stud
space and attach the next section, Figure 28-41.
Continue until the top of the stack reaches the register
box or lilting to which it will connect. Reduce the