Return Air and Exhaust Air Inlets
Grilles and registers are the two principal types of air inlets used to exhaust the air from a space or to return the air to the centrally located heating or cooling unit. The grilles are generally fixed-angle types because there is no need to direct air circulation when return air is involved.
Duct Run Fittings
Round and rectangular duct run fittings are available in a variety of different shapes and sizes, depending on the requirements of the air distribution system. Some duct run fittings are used only for cooling systems; others are designed for use in both heating and cooling systems. Duct run fittings can be purchased from manufacturers
and local supply houses, or they can be made locally. Making your own fittings requires knowledge of sheet-metal work. Components of a typical duct system are shown in Figure 7-4. Based on their function, these duct run fittings can be divided into the following principal categories:
• Supply-air and return-air bonnet or plenum (see Figure 7-8)
• Plenum and extended plenum takeoffs (see Figure 7-9)
• Trunk duct angles and elbows (see Figure 7-10)
• Stack angles and elbows (see Figure 7-11)
• Boot fittings (see Figures 7-12 and 7-13)
• Wall sections (see Figure 7-14)