4
INSPECTION & INSTALLATION
INCORRECT BENDS
Ducts shall not be crimped tightly against joist or truss members, or against pipes, wires, and other building materials.
Duct runs shall be made with the minimum practical length needed to make the connection from one fitting to the next. Excessive duct length and bends increase pressure drop and reduce overall system efficiency and performance. Ducts shall not be installed with excess length intended for future building changes.
Figure 11
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4.4 Routing, Sagging, & Snaking
Flexible air ducts and connectors should always be installed in the most direct route possible. Changing directions multiple times will increase the friction rate of the duct thus decreasing the air flow in the HVAC system. Flexible air ducts and connectors must be installed in the straight condition without sag. Extra supports should be used to prevent sag where 90° bends are made by placing straps both before and after the bend. Excessive sag creates more friction reducing air flow in the air distribution system.
INCORRECT ROUTING
Figure 12
Figure 13
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