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 existing temperature.

DUCT CONSTRUCTION

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.

Round Duct

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 longitudinal seam.

The duct system should be constructed in a way that avoids abrupt changes in size,

Figure 13-2. - Residentia1 duct system.