Instructions / Assembly
Chapter 28 Ductwork
Figure 28-47. A disposable air filter can be positioned within
a centrally located return air grille.
Baseboard grille
Floor grille
Wall grille
Figure 28-48. Return air grilles may be located in floor,
ceiling, wall, or baseboard.
floor plate can be cut from below the floor. Using the
stud space as a return-air duct requires sealing off the
stud space just above the grille opening with a 2" x 4"
wood block as shown in Figure 28-49.
Installing floor type or baseboard type grilles is
much the same as installing supply air registers in
those surfaces, Figure 28-50. Floor type and baseboard
grilles require larger holes than diffusers.
28.15.2 Basement Return-Air System
With the return-air grilles installed and the return
takeoff fittings attached to the return-air plenum, it is
only necessary to complete the runs from the grilles to
the furnace. This may be done through sheeted joist
and slud spaces, direct ducts, or a combination of the
two, Figure 28-51.
28.16 Insulation
Insulate all supply ducts and pipes installed in an
attic, crawl space, or other unhealed areas. Carefully
wrap the insulating material around each pipe and
secure with proper glue or by applying tape along the
seam, Figure 28-52.
WARNING: To avoid a fire hazard, the warm-air
plenum and branch ducts must be separated from
wood joists, floors, and other structural elements by at
least I" of clear space or insulation.
28.16.1 Leaks in Air Ducts
Over time, fabric-based duct tape grows brittle and
the glue dries out. This permits sections of duct to
Studs
Return air
grille
2" X 4" to seal stud
space above grille
Adjoining
Floor plate cut to
allow air passage
Metal
sheeting
Base
molding
Flooring
Figure 28-49. With wall-type grille openings, air is returned to the furnace through stud spaces, sheeted joist spaces, or ducts.