Table 2-2. - Recommended Gauges for Sheet-Metal Duct Construction

and piping systems. These obstructions must be avoided by fabricating the duct system to go around the obstacles. Do NOT run obstructions through duct systems because it creates turbulence that reduces the efficiency of the system. When the obstruction is an electrical obstruction, you should ensure all power is off and safety checked. When running the duct through an obstruction is absolutely unavoidable, the turbulence can be reduced by enclosing the obstruction in a streamlined collar (fig. 2-93).

Figure 2-93. - Easement around an obstruction in ducts.

FLEXIBLE CONNECTIONS

Most duct systems are connected to either a heating or a cooling system. These systems are generally electric motor driven to move air through theduct system. Therefore, all inlet and outlet duct connections to all fans or other equipment that may create vibration should be made with heavy canvas, as shown in figure 2-94.

The most common method of making connections between duct sections and fittings is the method of