In figure 13-2, the same basic system is
shown in a single-story house. The duct
system is located in the overhead and the
return air enters through the bottom of the
central air-handling unit. When the duct
system is located in a crawl space, basement,
or attic, it should be insulated to maintain the
In this section, basic sheet metal ducts,
both round and rectangular, are discussed.
Emphasis is placed on layout and pattern
requirements. Then fiberboard duct
construction and its use are discussed.
Straight sections of round duct are usually
formed from sheets rolled to a proper radius
and assembled with a longitudinal grooved
seam Each end of a round section is swaged
and assembled with the larger end of the
adjoining section butting against the swage.
Sections are held together by rivets, by sheet
metal screws, or by solder. Where solder is not
used, duct tape or liquid rubber (duct sealer)
should be used as a covering at all joints.
Rectangular ducts are generally constructed by
bending corners and by grooving along the
The duct system should be constructed in a
way that avoids abrupt changes in size,
Figure 13-2.Residentia1 duct system.